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Small, widely-dispersing, pelagic larvae are difficult to monitor through direct observation, but biophysical models can provide greater understanding of dispersal patterns. Here, we used a technique of reversing time in a biophysical model to estimate larval release sites of the blue crab, Callinectes sapidus, in the northern Gulf of Mexico by backtracking from known locations of postlarval settlement. We modeled surface ocean movement in reverse time from four settlement sites (Grand Isle, Louisiana; Ocean Springs, Mississippi; Dauphin Island, Alabama; and Pensacola, Florida). In the Gulf of Mexico, blue crab fisheries are managed at the state level. We found on average 73% of the larvae were traced back to larval release sites in the same state as settlement. Barrier island release sites accounted for 11% of settlement at Grand Isle and 17% at Dauphin Island. Less than 0.1% of larvae that settled in Grand Isle were tracked back to a known blue crab spawning area located to the south west, Ship Shoal. The distance traveled by larvae was highest in Pensacola and Grand Isle. The coefficient of variation of distance traveled was highest in Dauphin Island. The average distance traveled to each settlement location ranged from 31 to 124 km. Distance traveled explained 24% of empirical settlement numbers (F1,89 = 28.82, P < 0.001;R2 = 0.24). Settlement success was higher at release sites predicted by this study than at randomly generated sites suggesting female selection of larval release sites.

Many animals derive benefits from roosting communally but may also face increased risk of infectious disease transmission. In spite of recent high-profile disease outbreaks in roosting animals of conservation and public health concern, we currently lack general theory for how attributes of roosting animals and their pathogens influence pathogen spread among roosts and overall population impacts on roosting species. Here we develop a model to explore how roost size and host site fidelity influence the time for a pathogen to escape from its initial roost, overall infection prevalence, and host population size, for pathogens with density- or frequency-dependent transmission and varying virulence. We find that pathogens spread rapidly to all roosts when animals are distributed among a small number of large roosts, and that roost size more strongly influences spread rate for density-dependent than frequency-dependent transmitted pathogens. However, roosting animals that exhibit high site fidelity and distribute among a large number of small roosts are buffered from population-level impacts of pathogens of both transmission modes. We discuss our results in the context of anthropogenic change that is altering aspects of roosting behavior relevant to emerging pathogen spread.

Light‐level geolocator tags use ambient light recordings to estimate the whereabouts of an individual over the time it carried the device. Over the past decade, these tags have emerged as an important tool and have been used extensively for tracking animal migrations, most commonly small birds. Analysing geolocator data can be daunting to new and experienced scientists alike. Over the past decades, several methods with fundamental differences in the analytical approach have been developed to cope with the various caveats and the often complicated data. Here, we explain the concepts behind the analyses of geolocator data and provide a practical guide for the common steps encompassing most analyses – annotation of twilights, calibration, estimating and refining locations, and extraction of movement patterns – describing good practices and common pitfalls for each step. We discuss criteria for deciding whether or not geolocators can answer proposed research questions, provide guidance in choosing an appropriate analysis method and introduce key features of the newest open‐source analysis tools. We provide advice for how to interpret and report results, highlighting parameters that should be reported in publications and included in data archiving. Finally, we introduce a comprehensive supplementary online manual that applies the concepts to several datasets, demonstrates the use of open‐source analysis tools with step‐by‐step instructions and code and details our recommendations for interpreting, reporting and archiving.

Animal movement, whether for foraging, mate-seeking, predator avoidance, dispersal, or migration, is a fundamental aspect of ecology that shapes spatial abundance distributions, genetic compositions, and dynamics of populations. A variety of movement models have been used for predicting the effects of natural or human-caused landscape changes, invading species, or other disturbances on local ecology. Here we introduce the flow network—a general modeling framework for population dynamics and movement in a metapopulation representing a network of habitat sites (nodes). Based on the principles of physical transport phenomena such as fluid flow through pipes (Pouiselle’s Law) and analogously, the flow of electric current across a circuit (Ohm’s Law), the flow network provides a novel way of modeling movement, where flow rates are functions of relative node pressures and the resistance to movement between them. Flow networks offer the flexibility of incorporating abiotic and biotic conditions that affect either pressures, resistance, or both. To illustrate an application of the flow network, we present a theoretical invasion scenario. We consider the effects of spatial structure on the speed of invasion by varying the spatial regularity of node arrangement. In the context of invasion, we model management actions targeting nodes or edges, and consider the effects on speed of invasion, node occupation, and total abundance. The flow network approach offers the flexibility to incorporate spatial heterogeneity in both rates of flow and site pressures and offers an intuitive approach to connecting population dynamics and landscape features to model movement.

The mechanism by which new deltaic wetlands form is a complex suite of biological and physical processes that can modify one another. Understanding these processes and their interactions is imperative to successful coastal restoration. This study investigated the relationship between belowground plant biomass and sediment cohesion. We hypothesized that greater root densities increase shear strength, variably across plant communities, and that these communities are associated with distinct inundation regimes. A significant relationship was found between belowground biomass and surface shear strength when accounting for sediment grain size, water content, and organic matter content. Sites dominated by native graminoids or woody species had significantly higher shear strengths than unvegetated areas. However, sites dominated by Phragmites australis or forbs did not differ significantly in shear strength from the unvegetated sites. Sites dominated by Phragmites australis were also subject to significantly higher inundation rates during the previous water year than any other vegetation type. These results suggest that vegetation community differences lead to differences in shear strength that result in locally differential erosion rates, in turn modifying future geomorphology, hydrology, sedimentation, and vegetation distribution. This feedback implies that certain vegetation communities in wetland restoration projects could not only impart immediate erosion resistance to the substrate, but affect the long-term potential for land creation.

The decreasing average pH of the world's oceans, called ocean acidification, can be detrimental to marine organisms. Decreased pH causes dissolution of calcium carbonate shells, as well as changes to metabolism, behavior, growth, survival, and early development of many species; however, the impacts of lower pH on crustaceans have not been widely researched. This study investigated the effects of lower pH on the growth and survival of larval blue crabs Callinectes sapidus through laboratory experiments. Blue crab larvae live at the surface of the open ocean where the pH is decreasing with ocean acidification. A pH of 7.8 was used to mimic the average surface ocean pH predicted to be attained by 2,100 by the Intergovernmental Panel on Climate Change and was compared with a control pH of 8.2, the current average surface ocean pH. Larvae raised at the lower pH were 10% smaller and there was a 23% reduction in survival. Larval populations within an aquarium with a lower pH were more likely to exhibit ...

The 2010 Deepwater Horizon oil spill occurred during peak spawning season for many Gulf of Mexico fish and invertebrates. Early life stages of important fishery species were at risk to encounter crude oil. In this study, we investigated the effect of crude oil exposure on two life stages of the blue crab (Callinectes sapidus). We tested the effects of oil exposure on the survival and growth of larval (pelagic) and juvenile (estuarine) blue crabs as well as the effects of oil on the molt frequency of juveniles. Larval crabs exposed to crude oil showed no discernable growth or mortality differences when compared to non-exposed controls. Juvenile crabs exposed to oil also showed no differences in size but exhibited increased intermolt duration (time between molts). Our study suggests that different life-stages may respond differently when exposed to crude oil and that oil exposure negatively affects growth rate of juvenile blue crabs.

During migration, animals may experience high rates of mortality, but costs of migration could also be manifested through non-lethal carry-over effects that influence individual success in subsequent periods of the annual cycle. Using tracking data collected from light-level geolocators, we estimated total spring migration distance (from the last wintering sites to breeding sites) of tree swallows (Tachycineta bicolor) within three major North American flyways. Using path analysis, we then assessed direct and indirect effects of spring migration distance on reproductive performance of individuals of both sexes. When these data were standardized by flyway, females fledged 1.3 fewer young for every 1,017 km they traveled, whereas there was no effect of migration distance on reproductive success in males. In comparison, when these data were standardized across all individuals and not by flyway, longer migrations were associated with 0.74 more young fledged for every 1,017 km traveled by females and 0.26 more young fledged for every 1,186 km migrated by males. Our results suggest that migration distance carries over to negatively influence female reproductive success within flyways but the overall positive effect of migration distance across flyways likely reflects broader life-history differences that occur among breeding populations across the tree swallow range.

There have been an increasing number of observations of itinerancy in migratory songbirds, where individuals move among 2 or more widely separated areas during the “stationary” nonbreeding season. Knowledge of such movements and an understanding of what drives them are important for predicting how migratory populations will respond to environmental change. In this study, we investigated nonbreeding movements of the Tree Swallow (Tachycineta bicolor), an aerial insectivore that breeds across North America and spends the nonbreeding season around the Gulf of Mexico, Florida, Mexico, Central America, and the Caribbean. With year-round tracking data obtained from 133 light-level geolocators deployed at 12 breeding sites ranging from Alaska to Nova Scotia to North Carolina, we show that 44% of individuals made at least one large-scale movement (range: 301–1,744 km) within the nonbreeding range. The frequency of itinerancy decreased with longitude, such that 75% of individuals made a movement in the western portion of the nonbreeding range compared to only 31% in the east. Using the Normalized Difference Vegetation Index (NDVI) as a proxy for resource availability, we found that when individuals did move, they were more likely to move from sites where resources were deteriorating faster (a more negative change in NDVI prior to departure) than their destination sites. There was also evidence that individuals moved to destination sites with higher NDVI and temperature in the autumn, but not in the winter. Our results suggest movements of Tree Swallows during the nonbreeding season are influenced by resource availability, but because not all individuals used multiple nonbreeding sites, the density of individuals at a site and the level of competition may have also been a factor influencing nonbreeding season movements.

Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is not well understood. We examined geographical variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows ( Tachycineta bicolor ) originating from 12 North American breeding populations. A swallow's breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure. This resulted in subsequent effects on the arrival and departure schedules at autumn stopover locations and timing of arrival at non-breeding locations. This ‘domino effect’ between timing events was no longer apparent by the time individuals departed for spring migration. Our range-wide analysis demonstrates the lasting impact breeding latitude can have on migration schedules but also highlights how such timing relationships can reset when individuals reside at non-breeding sites for extended periods of time.

Migratory animals are declining worldwide and coordinated conservation efforts are needed to reverse current trends. We devised a novel genoscape-network model that combines genetic analyses with species distribution modeling and demographic data to overcome challenges with conceptualizing alternative risk factors in migratory species across their full annual cycle. We applied our method to the long distance, Neotropical migratory bird, Wilson's Warbler (Cardellina pusilla). Despite a lack of data from some wintering locations, we demonstrated how the results can be used to help prioritize conservation of breeding and wintering areas. For example, we showed that when genetic, demographic, and network modeling results were considered together it became clear that conservation recommendations will differ depending on whether the goal is to preserve unique genetic lineages or the largest number of birds per unit area. More specifically, if preservation of genetic lineages is the goal, then limited resources should be focused on preserving habitat in the California Sierra, Basin Rockies, or Coastal California, where the 3 most vulnerable genetic lineages breed, or in western Mexico, where 2 of the 3 most vulnerable lineages overwinter. Alternatively, if preservation of the largest number of individuals per unit area is the goal, then limited conservation dollars should be placed in the Pacific Northwest or Central America, where densities are estimated to be the highest. Overall, our results demonstrated the utility of adopting a genetically based network model for integrating multiple types of data across vast geographic scales and better inform conservation decision-making for migratory animals.Un Modelo de Redes de Panorama Poblacional para la Priorización de la Conservación de un Ave Migratoria Resumen Los animales migratorios están pasando por una declinación mundial y se requieren esfuerzos coordinados de conservación para revertir las tendencias actuales. Diseñamos un modelo novedoso de redes de panorama poblacional que combina el análisis genético con el modelado de la distribución de especies y los datos demográficos para sobreponerse a los obstáculos con la conceptualización de los factores alternativos de riesgo en las especies migratorias durante su ciclo anual completo. Aplicamos nuestro método al chipe de corona negra (Cardellina pusilla), un ave migratoria neotropical que recorre largas distancias. A pesar de la falta de datos de algunas localidades de invernación, mostramos cómo pueden usarse los resultados para ayudar a priorizar la conservación de las áreas de reproducción y de invernación. Por ejemplo, mostramos que cuando se consideraron en conjunto los resultados del modelado genético, demográfico y de redes queda claro que las recomendaciones de conservación diferirán dependiendo de si el objetivo es preservar linajes genéticos únicos o el mayor número de aves por unidad de área. Más específicamente, si el objetivo es la conservación de los linajes genéticos, entonces los recursos limitados deberían enfocarse en preservar el hábitat en la Sierra de California, la Cuenca de las Rocallosas, la costa de California (lugares en donde se reproducen los tres linajes genéticos más vulnerables) o en el oeste de México (en donde dos de los tres linajes más vulnerables pasan el invierno). Alternativamente, si el objetivo es la conservación del mayor número de individuos por unidad de área, entonces el financiamiento limitado debería aplicarse en el noroeste del Pacífico o en América Central, en donde se estima que las densidades poblacionales son las más altas. En general, nuestros resultados demostraron la utilidad de adoptar un modelo de redes basadas en la genética para la integración de datos a lo largo de escalas geográficas amplias y para informar de mejor manera la toma de decisiones de conservación para los animales migratorios.世界范围内迁徙动物的数量正在减少, 需要采取协调一致的保护措施来扭转目前的趋势。我们设计了一种新的遗传谱网络模型, 通过整合遗传分析与物种分布模型和种群统计数据, 来应对确定迁移物种在完整年周期中面临风险因素的挑战。我们将这一方法应用于一种长距离迁徙的新热带候鸟--黑头威森莺 (Cardellina pusilla)。尽管缺乏部分越冬地点数据, 我们仍展示了如何利用这些结果来确定优先保护的繁殖地和越冬地。例如, 当同时考虑遗传、种群统计和网络模型结果时, 可以明显发现, 针对不同的保护目标--保护独特的遗传谱系或确保单位面积内得到保护的鸟类数量最大化, 所得出的保护建议也不同。具体来说, 如果以保护遗传谱系为目标, 那么有限的资源应集中在保护加利福尼亚山脉、落基山盆地和加利福尼亚海岸的栖息地, 这些地区是黑头威森莺最濒危的三支遗传谱系的繁殖地, 或者集中保护墨西哥西部, 那里是三支最濒危遗传谱系中两支谱系的越冬地。然而, 如果以保护单位面积最大数量的个体为目标, 那么有限的保护资金应投向太平洋西北部或中美洲, 那里的鸟类密度估计值最高。总的来说, 我们的研究结果表明, 采用基于遗传的网络模型来整合跨越广阔地理范围的多类型数据是非常有用的, 并将更好地为迁徙动物的保护决策提供信息。【翻译: 胡怡思; 审校: 聂永刚】.

Blue crabs, Callinectes sapidus Rathbun, 1896, are ubiquitous along the Atlantic and Gulf coasts of the United States. These organisms play an integral role in the ecosystems of the Gulf of Mexico (GOM), where not only are they a keystone species, but are also socioeconomically important. The survival of embryonated eggs is necessary to ensure adequate recruitment into the next generation. Because the 2010 Deepwater Horizon oil spill (DWH) occurred during the peak of the blue crab spawning season, the incident likely impacted blue crab embryos. In order to assess the effect of oil on embryonic growth and development, we collected embryonated eggs from seven different female blue crabs from the GOM throughout the spawning season and exposed them to an oil concentration of 500 ppb (the approximate concentration of oil at the surface water near the site of the Deepwater Horizon oil rig). Exposure to oil at this concentration caused a significantly larger proportion of prezoeae versus zoeae to hatch from embryonated eggs in experiments lasting longer than 4 days. Exposure to oil did not significantly affect overall survival or development rate. The prezoeal stage is a little-studied stage of blue crab development. Though it may or may not be a normal stage of development, this stage has been found to occur in suboptimal conditions and has lower survival than zoeal stages. The larger proportion of prezoeae following prolonged exposure to oil thus indicates that crude oil at concentrations likely to be experienced by crabs after the DWH spill negatively impacted the development of blue crab embryos. In addition to providing insight into the effects of the Deepwater Horizon oil spill, this study sheds light on embryonic development in blue crabs, a critical, but poorly investigated phase of this important species’ life cycle.

For seasonal migrants, non-breeding regions can play different roles in the ecology of their annual cycles: as stopover habitat, overwintering habitat, or as a combination in which some individuals stop-over and others over-winter. Such functional variations can lead to variation in occupancy dynamics and migration phenology to these different regions. In this study, we used data from archived Doppler weather surveillance radar to compare site-occupancy and movement dynamics of a migratory songbird (tree swallow Tachycineta bicolor) between two non-breeding areas: southeastern Louisiana and central peninsular Florida, USA. Specifically, in each area, we 1) quantified long-term (1996–2012) non-breeding season occupancy dynamics, 2) quantified variation in timing of autumn migration, and 3) tested which climate variables along their respective flyways were best correlated with variation in dates of arrival. Additionally, we cross-validated the dynamics from archived radar with data from eBird, a large-scale citizen science database that provides an independent measure of avian occupancy. We found strong and significant correlations between radar-estimated and eBird-estimated occupancy dynamics in both Louisiana and Florida. Long-term Louisiana occupancy dynamics conformed to our hypothesis that this region acts as a combined stopover and overwintering region whereas Florida occupancy dynamics were akin to a traditional winter region. Arrival to Louisiana during the study period was much earlier and took place over a much shorter arrival window than did arrival to Florida, which showed much more gradual arrival over the course of several months. At both sites, annual variation in mean arrival date was best explained by the amount of precipitation along the lower portions of their respective migration flyways.

In mark–recapture studies conducted on fixed-area study sites, apparent (or “local”) survival (ϕ) is the product of the probabilities of true survival (S) and site fidelity to the sampling area (F). If marked individuals permanently emigrate from the study site, apparent survival will be biased low relative to true survival. Similarly, estimates of mate fidelity will be biased high because site fidelity is typically higher for individuals that reunite with their previous mates than among pairs that divorce. Here, we develop a method for calculating site fidelity that takes plot boundaries into account, based on a dispersal model estimated from local movements within a fixed study site. We use dispersal estimates to adjust apparent survival and mate fidelity for the effects of short-distance movements out of a fixed area. We demonstrate our method with a retrospective analysis of a published study of 2 species of sandpipers breeding sympatrically at a field site in western Alaska. Estimates of sur...

Twenty-eight species of migratory shorebirds rely on the coastlines of the northern Gulf of Mexico (NGOM) to fuel migrations to near-arctic breeding grounds. Shorebird species vary in their migration ecology: some species use a “jump” strategy, migrating long distances without stopping, while others use “skip” and “hop” strategies, stopping to refuel at shorter intervals along their journey. We compared stopover duration, body condition (fat scores and size-adjusted mass), and refueling rates (plasma metabolite concentrations), in three Calidrid sandpiper species (Calidris pusilla, C. mauri, and C. alpina) that differ in migration strategy after leaving the NGOM during spring. Results indicate that, while birds refueled at similar rates, C. alpina, an intermediate distance jump migrant, reached higher fuel stores before departing on migration than the hop and skip migrants, C. pusilla and C. mauri. C. alpina also spent more time on the NGOM than the other two species. Results suggest that NGOM habitats may be particularly important for migration success in C. alpina. This knowledge will help us predict the potential population level consequences of habitat loss due to global change on NGOM shorebird populations and develop conservation plans to mitigate these impacts.

It is well known that forest fragmentation reduces fecundity in several avian species, including wood thrush, Hylocichla mustelina, a migratory songbird that has been declining for several decades. However, I found that landscape-scale density in wood thrush was lower and population declines steeper in higher quality, less-fragmented landscapes (an inverse buffer effect) than in poor quality landscapes. These patterns suggest that wood thrush was not limited by availability of breeding habitat but that declines were primarily driven by non-breeding season events. A two-season model predicts that if this hypothesis is correct, breeding population trends will be negatively related to the strength of density dependence (b’) in the breeding season. To test this, a site-dependence model was used to construct fecundity-density curves and showed that landscape fragmentation affected the shape of density dependence. In good quality landscapes, the onset of strong density dependence was much more abrupt than in poorer quality landscapes and the realized strength of density dependence, b’, was lower in good quality landscapes. Population trends were negatively associated with b’, providing support for the non-breeding limitation hypothesis. The combination of the negative associations of trends with b’ and b’ with landscape quality explain the inverse buffer effect.

The 2010 Deepwater Horizon (DWH) oil spill in the northern Gulf of Mexico (NGOM) resulted in over 780million liters of crude oil spilling into Gulf waters. In an effort to disperse the oil, nearly 7.6million liters of dispersant was applied. Many commercially and recreationally important species reside in or near the area of the spill. The blue crab, Callinectes sapidus, is common in the NGOM and is both economically and ecologically important in this region. In this study, after exposing juvenile blue crabs to oil or a mixture of oil and dispersant we tested for relative expression of heat shock protein 90 (hsp90) and vitellogenin (vtg) by measuring their corresponding mRNA expression. We also monitored crabs over two molts to test for effects on growth. Expression of hsp90 was significantly downregulated, and we did not detect any effects of exposure to oil or oil/dispersant mixture on growth or vtg expression.

The coastline of the Gulf of Mexico in the United States is an important wintering and stopover region for migratory shorebirds. The Deepwater Horizon oil spill (April–August 2010) impacted more than 1700 km of this coastline and could potentially affect shorebirds through long-term exposure to toxins, degraded habitats, and altered food chains. We investigated the exposure to Deepwater Horizon oil of seven species of shorebirds that winter or stopover along the northern Gulf of Mexico. From October 2010 to May 2012, we captured and banded 691 shorebirds at six sites that experienced varying levels of oil contamination. Of birds sampled, 22 were lightly oiled, with species that forage on the coast having higher rates of oiling than those that forage in more estuarine habitats. Although only 8.6% of birds captured from October 2010 to May 2011 and 0.6% of the birds captured from August 2011 to June 2012 showed signs of oiling, an unknown, but potentially larger, number of shorebirds were likely exposed to indirect effects of the spill, such as decreased foraging time due to oiling of sites or disturbance from cleanup activities. Fuel stores and fattening rates of Dunlins (Calidris alpina) during spring migration, as measured using plasma metabolites, were not influenced by site oiling level. However, the level of disturbance at study sites was a significant predictor of both fuel stores and glycerol levels, suggesting that Dunlins stopping over during spring migration may have had difficulty reaching necessary fuel stores in spring 2011 due to disturbance from cleanup activity on oiled beaches. These effects from disturbance were only observed at sites with high cleanup activity, suggesting that the impact of oil-spill cleanup on shorebirds may be minimized by limiting cleanup activities to specific areas and times of day. RESUMEN Tasa de empetrolamiento e indices de condicion de aves costeras en el norte del Golfo de Mexico tras el derrame de petroleo de la Deepwater Horizon La costa del Golfo de Mexico en los Estados Unidos es una importante region de invernada y de puerto intermedio para aves costeras migratorias. El derrame de petroleo de la plataforma Deepwater Horizon (Abril – Agosto 2010) impacto mas de 1700 km de su costa y puede potencialmente afectar a las aves costeras a traves de la exposicion prolongada a toxinas, ambientes degradados, y cadena alimenticia alterada. Investigamos la exposicion al petroleo de la Deepwater Horizon por parte de siete especies de aves costeras que invernan o tienen paradas intermedias a lo largo del norte del Golfo de Mexico. De Octubre 2010 a Mayo 2012, capturamos y anillamos 691 aves costeras en seis sitios que mostraban niveles variables de contaminacion por petroleo. De las aves muestreadas, 22 estaban ligeramente empetroladas, con las especies que forrajean en la costa mostrando las tasas mas altas de empetrolamiento respecto a las que forrajean en ambientes mas estuarinos. Aun cuando solo el 8.6% de las aves capturadas entre Octubre de 2010 y Mayo de 2011 y el 0.6% de las aves capturadas entre Agosto de 2011 y Junio de 2012 mostraron senales de empetrolamiento, un numero desconocido pero potencialmente mayor de aves costeras han sido posiblemente expuestas a efectos indirectos del derrame, como ser disminucion en el tiempo de forrajeo debido a empetrolamiento de sitios o disturbios por actividades de limpieza del sitio. Los depositos de energia y la tasa de engordamiento del Playero comun (Calidris alpina) durante la migracion de primavera, mediada usando metabolitos plasmaticos, no se vieron influenciados por el nivel de empetrolamiento del sitio. Aun asi, el nivel de disturbio en el sitio de estudio fue un predictor significativo de tanto los depositos de energia como de los niveles de glicerol, sugiriendo que los Playeros comunes que se detienen durante la migracion de primavera pueden haber tenido dificultades en alcanzar depositos de energia necesarios en primavera del 2011 debido a disturbios por actividades de limpieza en playas empetroladas. Aun asi, los efectos de los disturbios fueron solo observados en sitios con alta actividad de limpieza, sugiriendo que el impacto de limpieza de derrame de petroleo en aves costeras puede ser minimizado limitando las actividades de limpieza a areas y horarios especificos.

One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in species that cross such barriers, and are thought to have evolved in response to seasonal variation in prevailing wind direction. We tested the hypothesis that migration routes vary seasonally with respect to the Gulf of Mexico in the tree swallow Tachycineta bicolor using solar geolocators attached and retrieved at 4 breeding sites in central North America. We found that 100 % of birds (n = 10) made a trans-Gulf flight of >850 km from Louisiana south to their wintering grounds in the Yucatan Peninsula in 12–36 hours, achieving minimum ground speeds as high as 32 m/s. Although most days during autumn migration were characterized by unfavorable headwinds blowing to the northwest, migration over the Gulf mostly occurred on days with strong winds blowing to the south. In contrast, in 8 of 9 (88 %) birds on spring migration returned from the wintering grounds towards Louisiana following a clockwise loop pat tern flying over land to the west around the Gulf. During this spring period there were few days with prevailing winds from the south to assist northward migration. Results suggest that, despite being up to three times further (ca. 2,700 km), a coastal cir- cum-Gulf spring migration represents the less risky route when wind conditions are not favorable. These findings also help to re solve a long-standing dispute in the literature concerning migration patterns between the US Gulf coast and Mexico, and provide insight into the factors shaping migration strategies of small songbirds migrating across large bodies of water.

Communal roosting is a taxonomically widespread phenomenon, with considerable variation in patterns of roost dynamics. Some organisms roost together in different locations each night (or day), whereas others roost in traditional locations each night, sometimes switching between roosts in the roost network. The behaviors that drive roost-site selection and the resulting patterns are not well understood. We created an individual-based model that simulates the daily aggregation of organisms into communal roosts. In the model, individuals move according to a movement rule integrating 2 independently adjustable behavioral drivers: roost fidelity, which leads individuals back toward their previous nights’ roost, and conspecific attraction, which leads individuals to congregate toward nearest conspecific neighbors. The model predicts that variable levels of aggregation will emerge under different combinations of these drivers, ranging from no aggregation to complete aggregation of individuals into their previous roosts. We tested to see which combination of drivers best predicts patterns of roost use in our study system of Tree Swallows (Tachycineta bicolor) in southeastern Louisiana in fall. Using Doppler weather radar data, we show that Tree Swallow roost sites remain consistent from night to night, and the birds return to one of several traditional roosts. Using radio telemetry, we show that individuals switch between these traditional roosts at minimum 22% of the time. Our results suggest that the formation of large communal roosts in Tree Swallows is driven by a combination of moderate conspecific attraction and strong, but not perfect, roost fidelity.

In their 2015 Current Biology paper, Streby et al. [1] reported that Golden-winged Warblers (Vermivora chrysoptera), which had just migrated to their breeding location in eastern Tennessee, performed a facultative and up to “>1,500 km roundtrip” to the Gulf of Mexico to avoid a severe tornadic storm. From light-level geolocator data, wherein geographical locations are estimated via the timing of sunrise and sunset, Streby et al. [1] concluded that the warblers had evacuated their breeding area approximately 24 hours before the storm and returned about five days later. The authors presented this finding as evidence that migratory birds avoid severe storms by temporarily moving long-distances. However, the tracking method employed by Streby et al. [1] is prone to considerable error and uncertainty. Here, we argue that this interpretation of the data oversteps the limits of the used tracking technique. By calculating the expected geographical error range for the tracked birds, we demonstrate that the hypothesized movements fell well within the geolocators’ inherent error range for this species and that such deviations in latitude occur frequently even if individuals remain stationary.

Many migratory species are in decline and understanding these declines is challenging because individuals occupy widely divergent and geographically distant habitats during a single year and therefore populations across the range are interconnected in complex ways. Network modeling has been used to show, theoretically, that shifts in migratory connectivity patterns can occur in response to habitat or climate changes and that habitat loss in one region can affect sub-populations in regions that are not directly connected. Here, we use a network model, parameterized by integrating long-term monitoring data with direct tracking of -100 individuals, to explain population trends in the rapidly declining Wood Thrush (Hylocichla mustelina) and to predict future trends. Our model suggests that species-level declines in Wood Thrush are driven primarily by tropical deforestation in Central America but that protection of breeding habitat in some regions is necessary to prevent shifts in migratory connectivity and to sustain populations in all breeding regions. The model illustrates how shifts in migratory connectivity may lead to unexpected population declines in key regions. We highlight current knowledge gaps that make modeling full life-cycle population demographics in migratory species challenging but also demonstrate that modeling can inform conservation while these gaps are being filled.

The 2010 Deepwater Horizon oil spill, the largest ever accidental release of oil into marine waters, affected hundreds of miles of US northern Gulf of Mexico coastline that is important habitat for migratory shorebirds. Shorebirds are particularly susceptible to oil contamination because of their subsurface probe-foraging behavior and reliance on intertidal habitat. More than one million migratory shorebirds representing 28 species were potentially exposed to Deepwater Horizon oil during their 2010–2011 nonbreeding season. Although only 8.6% of the shorebirds trapped from fall 2010 to spring 2011 showed visible signs of oiling, nonlethal effects and degradation of habitat can affect populations in ways that carry over into subsequent seasons. Here, we discuss how the spill could affect populations of migratory shorebirds through acute mortality, as well as through long-term and indirect pathways. We also discuss the potential impacts on ecosystems far from the spill, including prairie grasslands and the A...

The 2010 Deepwater Horizon oil release posed the challenges of two types of spill: a familiar spill characterized by buoyant oil, fouling and killing organisms at the sea surface and eventually grounding on and damaging sensitive shoreline habitats, and a novel deepwater spill involving many unknowns. The subsurface retention of oil as finely dispersed droplets and emulsions, wellhead injection of dispersants, and deepwater retention of plumes of natural gas undergoing rapid microbial degradation were unprecedented and demanded the development of a new model for deepwater well blowouts that includes subsurface consequences. Existing governmental programs and policies had not anticipated this new theater of impacts, which thereby challenged decisionmaking on the spill response, on the assessment of natural resource damages, on the preparation for litigation to achieve compensation for public trust losses, and on restoration. Modification of laws and policies designed to protect and restore ocean resources is needed in order to accommodate oil drilling in the deep sea and other frontiers.

A partially migratory population consists of non-migrant and migrant individuals that share a common site during one period of the annual cycle. In this paper, we derive the expected equilibrium population sizes of migrants and non-migrants and show how the abundance of one type is dependent on the other because their dynamics are coupled through densitydependent effects. We present an approach for developing hypotheses about how changes in the environment will influ ence partially migratory populations and for formulating testable predictions about the effects of future changes on the proportions of migrants and non-migrants. We apply this approach to a hypothesis put forward by Berthold that improved environmental conditions at the shared site will generally increase the number of non-migrants and decrease the number of migrants, and to a study by Nilsson et al. which observed an increase in the number of migrants in a partially migratory blue tit Cyanistes caeruleus population in Sweden, but an overall maintenance of the proportion of migrants.

Although stopover habitats are used by many species as refuelling stations during migration and can be critical for survival and successful reproduction, they are rarely incorporated in year-round population models and conservation strategies. We incorporate stopover habitat into a density-dependent population model and then use this model to examine how optimizing one-time land purchase strategies for a migratory population is influenced by variation in the quality and the strength of density-dependence in a stopover habitat used for both fall and spring migration. As the strength of the density-dependence in the stopover habitat increases, the optimal amount of stopover habitat purchased increases while the amount of habitat during the stationary periods of the annual cycle (breeding and wintering) decreases. Any change in the cost of purchasing stopover habitat affects investment strategies in all three periods of the annual cycle. When the quality of the stopover habitat is high, the optimal strategy is to invest in low-quality habitat during breeding and wintering and when the stopover habitat quality is low, the optimal strategy switches to investing in high-quality habitat during the stationary periods. We apply this model to a threatened warbler population and demonstrate how purchase decisions to conserve stopover habitat that are not coordinated with conservation actions on the breeding and wintering grounds can potentially result in a lower population carrying-capacity compared to considering habitat in all three periods of the annual cycle simultaneously. Our model provides potential guidelines for developing conservation strategies for animals that rely on refueling habitats between the stationary breeding and non-breeding periods of the migratory cycle.

Conservation strategies for migratory animals are typically based on ad-hoc or simple ranking methods and focus on a single period of the annual cycle. We use a density-dependent population model to examine one-time land purchase strategies for a migratory population with a breeding and wintering grounds. Under equal rates of habitat loss, we show that it is optimal to invest more, but never solely, in the habitat with the higher density dependence to habitat cost ratio. When there are two habitats that vary in quality within a season, the best strategy is to invest only in one habitat. Whether to purchase highor low-quality habitat depends on the general life history of the species and the ratio of habitat quality to habitat cost. When carry-over effects are incorporated, it is almost always optimal to invest in high-quality habitat during the season that produces the carry-over effect. We apply this model to a threatened warbler population and show the optimal strategy is to purchase more breeding than wintering habitat despite the fact that breeding habitat is over ten times more expensive. Our model provides a framework for developing year-round conservation strategies for migratory animals and has important implications for long-term planning and management.

Burrowing crabs of the genus Uca inhabit tidal mudflats and beaches. They feed actively during low tide and remain in their burrows when the tide is high. The timing of this activity has been shown to persist in the absence of external light and tidal cues, indicating the presence of an internal timing mechanism. Researchers report the persistence of several variations in locomotor activity under laboratory conditions that cannot be explained by a single circatidal clock. Previous studies supported two alternative hypotheses: the presence of either two circalunidian clocks, or a circadian and circatidal clock to regulate these activity rhythms. In this paper, we formulate mathematical models to describe and test these hypotheses. The models suggested by the literature contain some important differences beyond the frequency of proposed clocks, and these are reflected in the mathematical formulations and simulation results. One hypothesis suggests independent phase oscillators, while the other hypothesis suggests that they are coupled in anti-phase. Neither model is able to recover all of the variations in locomotor acitivity observed under laboratory conditions. However, we propose a new model that incorporates aspects of both existing hypotheses and is able to reproduce all laboratory observations.

Migratory animals are comprised of a complex series of interconnected breeding and nonbreeding populations. Because individuals in any given population can arrive from a variety of sites the previous season, predicting how different populations will respond to environmental change can be challenging. In this study, we develop a population model composed of a network of breeding and wintering sites to show how habitat loss affects patterns of connectivity and species abundance. When the costs of migration are evenly distributed, habitat loss at a single site can increase the degree of connectivity (mixing) within the entire network, which then acts to buffer global populations from declines. However, the degree to which populations are buffered depends on where habitat loss occurs within the network: a site that has the potential to receive individuals from multiple populations in the opposite season will lead to smaller declines than a site that is more isolated. In other cases when there are equal costs of migration to two or more sites in the opposite season, habitat loss can result in some populations becoming segregated (disconnected) from the rest of the network. The geographic structure of the network can have a significant influence on relative population sizes of sites in the same season and can also affect the overall degree of mixing in the network, even when sites are of equal intrinsic quality. When a migratory network is widely spaced and migration costs are high, an equivalent habitat loss will lead to a larger decline in global population size than will occur in a network where the overall costs of migration are low. Our model provides an important foundation to test predictions related to habitat loss in real-world migratory networks and demonstrates that migratory networks will likely produce different dynamics from traditional metapopulations. Our results provide strong evidence that estimating population connectivity is a prerequisite for successfully predicting changes in migratory populations.

Avian age-class discrimination is typically based on the completeness of the first prebasic molt. In several calidrid sandpiper species, juvenal flight feathers grown on Arctic breeding grounds are retained through the first three migrations. Thereafter, flight feathers are grown annually at temperate migratory stopover sites during the fall or on the subtropical wintering grounds. Standard methods for distinguishing age classes of sandpipers rely on a combination of traits, including body plumage, coloration of protected inner median covert edges, and extent of flight feather wear. We tested the ability of stable hydrogen isotope ratios in flight feathers (Df )t o distinguish young birds in their first winter through second fall from older adults in three calidrid sandpiper species, Western (Calidris mauri), Least (C. minutilla), and Semipalmated (C. pusilla) sandpipers. We compared the apparent reliability of the isotope approach to that of plumage-based aging. The large expected differences in Df values of flight feathers grown at Arctic versus non-Arctic latitudes enabled use of this technique to discriminate between age-classes. We determined Df values of known Arctic-grown feathers from juveniles that grew their flight feathers on the breeding grounds. Flight feather Df values of southward-migrating adults showed bimodal distributions for all three species. Negative values overlapped with species-specific juvenile values, identifying putative second fall birds with high-latitude grown juvenal feathers retained from the previous year. The more positive values identified older adults who grew their feathers at mid- and low latitudes. Importantly, Df analysis successfully identified first-winter and second-fall birds not detected by plumage-based aging. Flight feather wear alone was a poor basis for age classification because scores overlapped extensively between putative second fall birds and older adults. Flight feather hydrogen isotope analysis enables more definitive assignment of age classes when standard plumage methods are unreliable. RESUMEN. El ande is´

Migration is widespread among animals, but the factors that influence the decision to migrate are poorly understood. Within a single species, populations may be completely migratory, completely sedentary or partially migratory. We use a population model to derive conditions for migration and demonstrate how migratory survival, habitat quality and density dependence on both the breeding and non-breeding grounds influence conditions for migration and the proportion of migrants within a population. Density dependence during the season in which migratory and sedentary individuals use separate sites is necessary for partial migration. High levels of density dependence at the non-shared sites widen the range of survival values within which we predict partial migration, whereas increasing the strength of density dependence at the shared sites narrows the range of survival values within which we predict partial migration. Our results have important implications for predicting how contemporary populations with variable migration strategies may respond to changes in the quality or quantity of habitat.

Measures of animal behavior can be used in a variety of situations to make inferences about the environment and population status. Work by our research group shows that migratory shorebirds adjust their usage of, and behavior at, stopover sites in response to environmental conditions. Motivated by this, we built an individual-based model of migrating shorebirds moving through a sequence of alternating small and large stopover sites. Birds at larger sites are safer from predators, but we assumed that less food is available than at small sites. In the model, both predation risk and food intake are densitydependent, and the behavior of migrants is controlled by two rules: one that determines whether a bird will depart a stopover site, and one that controls the individual's foraging versus vigilance intensity. The optimal behavior is calculated by maximizing a payoff function that depends on arrival date and arrival energy stores at the final site. We used this model to predict mass gain, foraging intensity, and usage by migrants of small and large sites under various conditions. We examined the effects of a flyway-wide reduction in the amount of food, a flyway-wide increase in predation danger, and the effects of lowering the overall population size. The mass action of many individuals, each optimizing its migration timing and routing, leads to the emergence of distinctive patterns of behavior and site choice under these differing environmental conditions. When food availability is reduced throughout the flyway, our model predicts that foraging intensity increases at every stopover site, thereby forcing birds to accept greater danger to maintain the fitness benefit of a timely arrival to the breeding area. A flyway-wide increase in predation danger results in fewer migrants choosing (and/or migrants staying a shorter time at) small stopover sites, balanced by a higher usage of large sites. These effects contrast with what is observed under true population declines, when the usage of both small and large sites declines.

Benthic infaunal communities are important components of coastal ecosystems. Understanding the relationships between the structure of these communities and characteristics of the habitat in which they live is becoming progressively more important as coastal systems face increasing stress from anthropogenic impacts and changes in climate. To examine how sediment characteristics and infaunal community composition were related along the northern Gulf of Mexico coast, we sampled intertidal infaunal communities at seven sites covering common habitat types at a regional scale. Across 69 samples, the communities clustered into four distinct groups on the basis of faunal composition. Nearly 70% of the variation in the composition of the communities was explained by salinity, median grain size, and total organic content. Our results suggest that at a regional level coarse habitat characteristics are able to explain a large amount of the variation among sites in infaunal community structure. By examining the relationships between infaunal communities and their sedimentary habitats, we take a necessary first step that will allow the exploration of how changes in habitat and community composition influence higher trophic levels and ecosystem scale processes.

Summary 1 There are very few general guidelines available to improve the process of eradicating invasive species. We addressed the basic question of whether it is more efficient to prioritize the removal of outliers or core populations of an invasive grass, Spartina alterniflora. 2 We used a structured model in which the population of the invasive species is partitioned into different classes based on local conspecific density in order to investigate density-based eradication strategies. 3 The Spartina population at a Pacific coast estuary in Washington state, USA, is subject to an Allee effect: at low density plants produce fewer propagules than in high-density coalesced meadows. Plants at low density, however, are able to spread faster vegetatively. We used a genetic algorithm to find the optimal division of resources between removal of high-density and low-density plants. We explored the consequences of the Allee effect, contrasting financial budgets available for control operations and the inclusion of seedling control in addition to the control of mature plants. 4 We found that the optimal strategy was dependent on the annual budget available for control. At low and medium budgets, it was necessary to remove the low-density plants first to achieve eradication, but if more money was available then the optimal strategy was to prioritize high-density areas. 5 Without an Allee effect the optimal strategy would always be to prioritize the removal of fast-growing, low-density sub-populations. Seedling control did not change the optimal strategy but did, in some cases, reduce the cost of eradication. 6 Synthesis and applications. Given the uncertainty in future budgets allocated for control of invasive Spartina, we recommend a strategy that prioritizes the removal of low-density subpopulations of S. alterniflora over high-density subpopulations. The Allee effect in this system is not sufficiently strong to outweigh the importance of the rapid vegetative spread of the plants at low density.

Results from both a spatially explicit stochastic simulation model and a spatially implicit deterministic model show that a weak Allee effect can slow the spread of an invasive plant, Spartina alterniflora, in a Pacific Coast estuary. The mean rate of spread with the Allee effect is ∼19%; removing the Allee effect results in a mean rate of spread of ∼31%. Sensitivity analysis both with and without the Allee effect reveal that seedling establishment, inflorescence density, and outcrossed seed production are key factors determining invasion rate. When there is an Allee effect, the invasion rate is sensitive to variation in self-pollinated seed production. By structuring the population according to density classes instead of the more usual age or stage classes, the deterministic model demonstrates a novel way of representing density dependence and an Allee effect in population biology. This approach could be applied to model the population dynamics of any species that spreads from multiple foci and in which these foci later coalesce.

We review and synthesize recent developments in the study of the spread of invasive species, emphasizing both empirical and theoretical approaches. Recent theoretical work has shown that invasive species spread is a much more complex process than the classical models suggested, as long range dispersal events can have a large influence on the rate of range expansion through time. Empirical work goes even further, emphasizing the role of spatial heterogeneity, temporal variability, other species, and evolution. As in some of the classic work on spread, the study of range expansion of invasive species provides unique opportunities to use differences between theory and data to determine the important underlying processes that control spread rates.

It is usually assumed that pollen availability does not limit reproduction in wind-pollinated plants. Little evidence either supporting or contradicting this assumption exists, despite the importance of seed production to population persistence and growth. We investigated the role of pollen limitation in an invasive estuarine grass ( Spartina alterniflora ), with a manipulative pollen supplementation and exclusion experiment in areas of high population density and at the low-density leading edge of the invasion. We also quantified pollen deposition rates on stigmas and pollen traps along a windward to leeward gradient. We found pollen impoverishment at the low-density leading edge of a large invasion, causing an 8-fold reduction in seed set. We found 9-fold more pollen on stigmas of high-density plants than on those of low-density plants. Pollen deposition rates on stigmas and traps did not increase downwind of low-density plants but did increase downwind of high-density plants and dropped off precipitously across a gap that lacked pollen donors. The delay of appreciable numbers of seed caused by pollen limitation persists for decades until vegetative growth coalesces plants into continuous meadows, and this Allee effect has slowed the rate of spread of the invasion.

Summary 1 Spartina alterniflora sets very little viable seed at the leading edges of an invasion in Willapa Bay, Washington, USA, where it was introduced c. 100 years ago. This largely outbreeding, rhizomatous grass recruits into previously unoccupied areas at low density, so young plants initially grow isolated from one another but eventually coalesce to form continuous meadows. 2 Isolated recruits set approximately one-tenth the seed of meadow plants at five sites, spread over the 230 km2 of Willapa Bay mudflats, and this seed germinated at only one-third the rate observed in meadow plants. 3 The consistent patterns suggested that the low seed set in the isolated plants was largely due to the demographic effects of density. Differences between sites in the incidence and amount of seed set and germination rate indicated, however, that there was some environmental influence. 4 These data imply that plants in newly invaded, low-density areas produce little viable seed until rhizomatous growth brings them into close contact. This Allee effect could substantially reduce the rate of invasion.

The Blue Crab, Callinectes sapidus, is a commercially, culturally, and ecologically significant species in the Gulf of Mexico (GOM), whose offshore stages were likely impacted by the Deepwater Horizon oil spill (DWH). To test for DWH effects and to better understand the planktonic ecology of this species, we monitored Callinectes spp. megalopal settlement and condition at sites within and outside of the spill extent during and one year after the DWH. We tested for DWH effects by comparing 2010 settlement against baseline data available for two sites, and by testing for differences in settlement and condition inside and outside of the spill extent. We also developed time series models to better understand natural drivers of daily settlement variation (seasonal and lunar trends, hydrodynamics, wind) during 2010 and 2011. Overall, we found that neither megalopal settlement nor body weight were significantly reduced at oiled sites, but that high unexplained variation and low statistical power made detection of even large effects unlikely. Time series models revealed remarkably consistent and relatively strong seasonal and lunar trends within sites (explaining on average 28% and 9% of variation, respectively), while wind and hydrodynamic effects were weak (1-5% variation explained) and variable among sites. This study provides insights into DWH impacts as well as the natural drivers of Callinectes spp. megalopal settlement across the northern GOM.

We describe the results of a World Ocean Circulation Experiment (WOCE) survey (line P1W) from the open Pacific Ocean, through the Bussol' Strait and across the Sea of Okhotsk. Observations are presented of distributions of temperature and salinity, dissolved oxygen and nutrients, and some derived quantities. Discussion centers on the distribution of the Sea of Okhotsk component of the North Pacific Intermediate Water mass and its properties. The Sea of Okhotsk has been suggested as the only location where deep convection may occur within the North Pacific or its marginal seas. Our analysis suggests that the surface σθ = 26.85 has recently been ventilated, and arguments might be made to suggest that ventilation has occurred to σθ = 27.05. This is discussed here, but detailed evidence is covered in a companion paper analyzing CFC observations. The Okhotsk component of the North Pacific Intermediate Water extends to substantially greater depths and densities, and so some other process is needed to create the denser water mass.

Metapopulation models are widely used to study species that occupy patchily distributed habitat, but are rarely applied to migratory species, because of the difficulty of identifying demographically independent subpopulations. Here, we extend metapopulation theory to describe the directed seasonal movement of migratory populations between two sets of habitat patches, breeding and non-breeding, with potentially different colonization and extinction rates between patch types. By extending the classic metapopulation model, we show that migratory metapopulations will persist if the product of the two colonization rates exceeds the product of extinction rates. Further, we develop a spatially realistic migratory metapopulation model and derive a landscape metric—the migratory metapopulation capacity—that determines persistence. This new extension to metapopulation theory introduces an important tool for the management and conservation of migratory species and may also be applicable to model the dynamics of two host–parasite systems.

Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore. Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival. We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows ( Tachycineta bicolor ) and barn swallows ( Hirundo rustica ) from North America and Europe, using measurements of corticosterone from feathers (CORT f ) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORT f differed with respect to instrumentation. Thus, to the extent that CORT f reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs.