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Effective wildlife conservation requires understanding diet composition and its consequences for population demography. Generalist predators consume a wide range of prey species and are therefore less sensitive to changes in prey abundance than specialists, but their reproductive success can still be driven by a primary prey species. We assessed breeding season diet of an at-risk population of American Goshawks (Accipiter atricapillus) across two ecological zones (coastal and transitional) on the south coast of British Columbia. We used three methods: egested pellets, prey remains, and nest cameras. We further assessed the impact of diet specialization and diet diversity on goshawk productivity. Diet composition and diversity differed among sample sources (pellets, pooled pellets-and-remains, cameras) and between measurements (biomass vs. counts of prey items), highlighting the importance of transparent methodology in raptor diet studies. Goshawks consumed 32 identified prey species but pine squirrels (Tamiasciurus spp.) dominated their diet in both ecological zones (14–61% of biomass), which indicated that pine squirrels may be a primary prey for this population. Diet of coastal zone goshawks contained slightly more birds and fewer hares than diet of transitional zone goshawks, consistent with the hypothesis that goshawk diet reflects local prey abundance. Goshawk pairs at 12 nests monitored with nest cameras fledged 1.4 ± 0.8 young per nest, but we found no evidence to support a correlation between diet diversity or dietary specialization and goshawk productivity. Our results suggest goshawks in this region act as functional specialists on locally abundant prey resources, but more research is needed to understand how variation in prey abundance affects goshawk diet and demographics in this temperate rainforest generalist. La conservación efectiva de la vida salvaje requiere comprender la composición de la dieta y sus consecuencias para la demografía poblacional. Los depredadores generalistas consumen una amplia variedad de especies presa y, por lo tanto, son menos sensibles a los cambios en la abundancia de presas que los especialistas, pero su éxito reproductivo aún puede depender de una especie presa principal. Evaluamos la dieta durante la temporada de cría de una población en riesgo de Accipiter atricapillus a lo largo de dos zonas ecológicas (costera y de transición) en la costa sur de la Columbia Británica. Utilizamos tres métodos: egagrópilas regurgitadas, restos de presas y cámaras de nidos. Además, evaluamos los impactos de la especialización y de la diversidad de la dieta en la productividad de A. atricapillus. La composición y la diversidad de la dieta difirieron entre las fuentes de muestreo (egagrópilas, egagrópilas y restos combinados, cámaras) y entre las mediciones (biomasa vs. recuento de presas), destacando la importancia de utilizar una metodología transparente en los estudios de dieta de rapaces. Los individuos de A. atricapillus consumieron 32 especies de presas identificadas, pero las ardillas de pino (Tamiasciurus spp.) dominaron su dieta en ambas zonas ecológicas (14–61% de la biomasa), lo que indica que las ardillas de pino pueden ser una presa principal para esta población. La dieta de los individuos de A. atricapillus de la zona costera incluyó ligeramente más aves y menos liebres que la dieta de los individuos de la zona de transición, lo que es consistente con la hipótesis de que la dieta de A. atricapillus refleja la abundancia local de presas. Las parejas de A. atricapillus en 12 nidos monitoreados con cámaras en nido criaron 1.4 ± 0.8 juveniles por nido, pero no encontramos evidencia que respalde una correlación entre la diversidad o la especialización de la dieta y la productividad de A. atricapillus. Nuestros resultados sugieren que A. atricapillus en esta región actúa como un especialista funcional sobre los recursos de presas localmente abundantes, pero se necesita más investigación para comprender cómo la variación en la abundancia de presas afecta la dieta y la demografía de A. atricapillus, una especie generalista del bosque templado. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Dam construction projects have created opportunities for water security, targeted flood protection, and energy production but at the cost of increasing anthropogenic pressure on affected aquatic ecosystems. Wetland ecosystems are often among the most vulnerable, as underlying hydrological regimes influence overall wetland structure and function. Marsh bird species are wetland and riparian habitat specialists, many of which are experiencing population declines across North America. We examined how the alteration of hydrological regimes for generating hydroelectric power affected the occurrence of secretive marsh bird species in the western montane region of British Columbia, Canada. We established survey stations in wetlands across 2 regions, the West Kootenay and the Columbia Wetlands, sampling across a spectrum of hydrological regimes and other potentially relevant factors. At each station, we assessed wetland occupancy during the breeding season using broadcast‐callback surveys focused on 5 secretive marsh bird species: American bittern (Botaurus lentiginosus), American coot (Fulica americana), pied‐billed grebe (Podilymbus podiceps), sora (Porzana carolina), and Virginia rail (Rallus limicola). Additionally, we measured vegetation structure and the proximity and size of nearby water bodies for each survey station. We then used occupancy models to assess important correlates behind wetland occupancy for these marsh bird species, considering water management operations, regional differences, and local‐ and landscape‐level wetland characteristics. Secretive marsh bird species were more likely to occupy wetlands in areas with less frequently altered hydrological regimes. Occupancy models highlighted local‐ and landscape‐level characteristics as important correlates for wetland occupancy by marsh birds. Wetlands with frequently altered hydrological regimes had more open water cover and less tall vegetation present, conditions that were negatively associated with occupancy. Altered wetlands in this study were farther from the next nearest wetland, which was also negatively associated with occupancy. We suggest reservoir management is altering vegetation communities within these wetlands, indirectly promoting lower occupancy of secretive marsh bird species. [ABSTRACT FROM AUTHOR]

The abundance of a widespread brood parasite, the Brown-headed Cowbird (Molothrus ater), has decreased by ∼30% in North America over the past 5 decades. Within a community, brood parasite abundance may be expected to positively correlate with host brood parasitism frequency and intensity, but evidence for this correlation is mixed. Few studies have examined if long-term changes in brood parasite abundance have resulted in changes to host parasitism frequency. We measured cowbird abundance, brood parasitism frequency and intensity of 4 riparian songbird species, and host abundance and richness in 2001–2004 and 2012–2014 in riparian vegetation of the south Okanagan Valley of British Columbia, Canada. We compared our data to historical data for the same parameters previously collected between ∼1960 and the early 1990s in the same area. We found that cowbird abundance decreased by ∼80% over 2 decades in the Okanagan Valley, mirroring or exceeding regional-scale trends. Host abundance and richness increased as cowbird abundance decreased. However, songbird brood parasitism frequency and intensity either increased or remained relatively high over more than 4 decades. We discuss possible explanations for this apparent disconnect between brood parasite abundance and host parasitism frequency and intensity, which offer opportunity for further study. Temporal changes in brood parasite abundance, such as the decline of Brown-headed Cowbirds in North America and the Common Cuckoo (Cuculus canorus) in Europe, should not be assumed to lead to correlated changes to host parasitism frequency and intensity. La abundancia de un parásito de nidadas ampliamente distribuido, el tordo Molothrus ater, ha declinado un ∼30% en Norteamérica a lo largo de las últimas 5 décadas. Dentro de una comunidad, se podría esperar que la abundancia de los parásitos de puestas se correlacione positivamente con la frecuencia e intensidad de parasitismo de puestas del hospedero, pero la evidencia al respecto es mixta. Pocos estudios han examinado si a largo plazo los cambios de abundancia de parásitos de puestas han resultado en cambios de frecuencia de parasitismo del hospedero. Medimos la abundancia del tordo Molothrus ater, la frecuencia e intensidad de parasitismo de puestas de 4 aves canoras riparias, y la abundancia y riqueza del hospedero en 2001–2004 y 2021–2014 en vegetación riparia del sur de Okanagan Valley en British Columbia, Canadá. Comparamos nuestros datos con datos históricos para los mismos parámetros colectados previamente entre ∼1960 y los inicios de 1990s en la misma zona. Encontramos que la abundancia del tordo Molothrus ater disminuyó un ∼80% a lo largo de 2 décadas en Okanagan Valley, reflejando o superando tendencias a escala regional. La abundancia y riqueza del hospedero aumentó conforme la abundancia del tordo Molothrus ater disminuyó. Sin embargo, la frecuencia e intensidad del parasitismo de puestas de las aves canoras se incrementó o permaneció relativamente alto por más de 4 décadas. Discutimos posibles explicaciones acerca de la aparente desconexión entre la abundancia del parásito de puestas y la frecuencia e intensidad del parasitismo del hospedero, que abre oportunidades de realizar futuros estudios. Cambios temporales en abundancia de parásito de puestas, como el declive del tordo Molothrus ater en Norteamérica y del cuco común (Cuculus canorus) en Europa no deben suponer cambios correlacionados en la frecuencia e intensidad del hospedero del parásito. Palabras clave: British Columbia, dinámica de poblaciones, interferencia competitiva, Okanagan Valley, parasitismo múltiple, parásitos de puestas, tasa de parasitismo. [ABSTRACT FROM AUTHOR]

Habitat use of indicator species is used to prioritize management activities. However, habitat use can vary temporally in response to changes in predation risk and foraging rewards. We deployed satellite tags on 20 black oystercatchers (Haematopus bachmani) in four regions of British Columbia, Canada, to examine habitat use and selection decisions across seasonal, diel and tidal cycles. We characterized the shoreline in each region and used GLMMs to investigate how habitat characteristics influenced shoreline use by tracked birds. For individuals, we estimated home range size and the frequency key features of the shoreline were re‐visited. Black oystercatchers generally made greater‐than‐expected use of rocky islets and shoreline with freshwater outflows, less tree cover and greater intertidal area. However, while black oystercatchers preferred islets and shoreline with less tree cover at most/all time periods, they only exhibited preferences for greater intertidal area during low tides, and preferences for shoreline with freshwater outflows during the nonbreeding season, day, and high tides. Individual home ranges, on average, contained 46 km of shoreline (range: 12–156 km) and individuals used 10.4 km (range: 6.7–13.9 km). Individuals made greater use of larger islets with less tree cover that were closer to outflows, and greater use of outflows associated with larger streams, greater intertidal areas and gravel substrates. Black oystercatchers' habitat preferences likely reduce predation risk (rocky islets and shoreline with less tree cover) and increase foraging rewards (shoreline with freshwater outflows, greater intertidal area, and gravel substrates). However, habitat preferences appear sensitive to constraints on movement in the breeding season and changes in foraging rewards across the diel and tidal cycle, highlighting the importance of examining habitat use at multiple temporal scales. Black oystercatchers are considered indicators of rocky intertidal health; therefore, critical habitat is expected to be important for a suite of wildlife dependent on safe and productive coastline. [ABSTRACT FROM AUTHOR]

Dams and reservoirs alter natural water flow regimes with adverse effects on natural ecosystems. Quantifying and reducing these effects are important as global demands for energy and water, and the number of dams and reservoir, increase. However, costs and logistic constraints typically preclude experimental assessment of reservoir effects on the environment. We developed a stochastic individual-based model (IBM), parameterized using empirical data, to estimate the annual productivity of yellow warblers that breed in riparian habitat within the footprint of the Arrow Lakes Reservoir in British Columbia, Canada. The IBM incorporated information on breeding phenology, nest site selection, brood parasitism, daily nest survival, re-nesting probabilities and post-fledging survival. We used the IBM to estimate the effect of four different water management scenarios on annual productivity. We found that the IBM accurately estimated average nest success (0.39 ± 0.10 SD), the proportion of females that produced at least one fledgling during a breeding season (0.56 ± 0.11), and annual fledging success (2.06 ± 0.43) under current conditions. The IBM estimated that reservoir operations currently reduce the annual productivity of this population by 37%, from an average of 1.62 to 1.06 independent young/female. Delaying when reservoir water levels reach 435m asl (the minimum elevation occupied by yellow warblers) by approximately 2 weeks was predicted to increase annual productivity to 1.44 independent young/female. The standardized effect on annual productivity of reducing the maximum elevation of the reservoir so that yellow warbler habitat is not inundated (Cohen's d = 1.52) or delaying when water is stored (Cohen's d = 0.83) was primarily driven by inundation effects on post-fledging survival. Reservoir operation effects on breeding birds will be species specific, but this IBM can easily be modified to allow the environmental impacts on the entire breeding bird community to be incorporated into water management decisions. [ABSTRACT FROM AUTHOR]

Leach's Storm Petrels Oceanodroma leucorhoa were listed as Vulnerable by the IUCN in 2018. Population declines in the western North Atlantic are associated with low annual adult survival rates, but trends and vital rates of populations in the eastern North Pacific are poorly known. To address this knowledge gap, we estimated the annual apparent survival of breeding adults at two colonies off the coast of British Columbia (Rock Islets: 52°20'40"N, 131°14'10"W and Cleland Island: 49°10'17"N, 126°05'28"W), using capture-mark-recapture data collected between 2006 and 2010. Transient models received substantially more support than standard Cormack-Jolly-Seber models, suggesting that the initial capture and banding reduced burrow fidelity. The model-averaged annual apparent survival rates for both colonies were high (estimate for each colony = 0.975 ± 0.011), compared to rates reported for colonies in the western North Atlantic (< 0.80). Capture effects reduced annual apparent survival estimates for the first year after capture by ca. 6%. Higher apparent adult survival at colonies in the eastern North Pacific may be due to lower exposure to direct and indirect anthropogenic stressors while foraging (specifically, marine oil and gas infrastructure) and reduced avian predation by gulls at breeding colonies. The high survival rates we found suggests that eastern North Pacific populations of Leach's Storm Petrels are under less stress than those in the western North Atlantic. [ABSTRACT FROM AUTHOR]

Tree cavities provide a critical resource for cavity-nesting animals, and high quality cavities can be difficult for animals to acquire in habitats where competition is high. We investigated the breeding performance of Lewis's Woodpeckers in three habitat types in British Columbia, Canada in 2013 and 2014. We also assessed whether the number of nest competitors and cavity availability influenced the habitat specific breeding performance of this threatened cavity nesting species. We found that daily nest survival rate was lower in burned habitat (0.15 ± 0.08 (0.05–0.37)) than in live pine (0.72 ± 0.10 (0.51–0.87)) or cottonwood (0.69 ± 0.09 (0.51–0.83)) habitats. However, hatching success (the proportion of eggs that hatch) was lower in live pine habitat (0.59 ± 0.09 95% CI) than burned (0.77 ± 0.19 95% CI) or cottonwood (0.80 ± 0.07 95% CI) habitat, and the fledging success of successful nests in live pine and burned habitat (1.86 ± 0.31 and 1.88 ± 0.59 95% CI, respectively) was slightly lower than in cottonwood habitat (2.61 ± 0.45 95% CI). Consequently, Lewis's Woodpeckers in cottonwood habitat produced more fledglings per nesting attempt (2.05 ± 0.49 95% CI) than in live pine (1.53 ± 0.35 95% CI) or burned (0.79 ± 0.49 95% CI) habitat. Habitats differed in the number of nesting competitors and the number of suitable cavities surrounding active Lewis's Woodpecker nests. Our results showed that cavity density best explained breeding performance differences although the mechanisms remain unclear. There was no evidence that the number of heterospecific nest competitors, including the invasive European Starling (Sturnus vulgaris), explained or influenced Lewis's Woodpecker breeding performance. Cavity density influenced the productivity of successful nests but did not explain habitat differences in hatching success or daily nest survival. Further work is required to understand the mechanistic basis for the habitat specific breeding performance of Lewis's Woodpeckers. Habitat differences in breeding performance in British Columbia are not consistent with those in other regions, highlighting the importance of regionally-specific demographic data for managing species at risk. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the effect of extreme climate events on the adult survival rates of three auk species, namely, Cassin's Auklet (Ptychoramphus aleuticus), Rhinoceros Auklet (Cerorhinca monocerata) and Tufted Puffin (Fratercula cirrhata). The species breed in Triangle Island, British Columbia. The results of the study showed that only the Cassin's Auklet population is adversely affected with climate change.

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The article presents a study on the survival of a cohort of Tufted Puffin juveniles based on wing length, date, and mass at fledging and age at first return at Triangle Island, British Columbia. The study evaluates characteristics of fledgings which influence local survival and effects on individual fitness and rate of population growth age at survival recruitment. Results show that survival of fledgings have increased with wing length for local survival while mass and date have weaker effects.

We investigated variation in morphology of American Dippers (Cinclus mexicanus) in the Chilliwack River watershed, British Columbia in relation to gender, age and migratory habit. Male dippers had linear dimensions that were 2-9% longer and, on average, were 16% heavier than females. Adults (AHY) were the same structural size as yearlings (HY). Yearlings, however, had shorter and more rounded wings than adults providing support for the hypothesis that an increased vulnerability to predation may lead to selection for traits that improve take-off performance and maneuverability. Yearlings also had shorter tails suggesting other selective pressures shape tail morphology. Dippers in this population may be sedentary or migrate short distances to breed at higher elevations. We found no evidence that wing or tail morphology varied with migratory habit or that sedentary dippers, that have higher reproductive success, are larger or heavier than migrants. Received 1 November 2007. Accepted 11 May 2008. [ABSTRACT FROM AUTHOR]

Natal dispersal is a complex process that involves decisions about when to leave the natal territory, how to move through the landscape, and where to settle. We investigated what factors influence the timing of dispersal and local recruitment of American Dippers (Cinclus mexicanus Swainson, 1827) in Chilliwack, British Columbia. We monitored 102 fledglings from 30 broods between 2003 and 2005. Survival to 5 days after fledging was high (>80%), but individuals fledging early in the season and at an older age had higher survival than those fledging later and younger. Fifty-four percentage of surviving fledglings dispersed within 14 days of nest departure. Females and individuals that spent more time foraging were more likely to disperse within 14 days than males and individuals that foraged less. For those that dispersed, individuals that fledged early in the season and at older ages spent less time in their natal territory. Approximately 10% (10/82) of dispersing individuals were known to recruit locally. Local recruitment of individuals that delayed dispersal was higher than local recruitment of individuals dispersing early. Our study demonstrates that fitness benefits associated with extended natal philopatry are not restricted to cooperatively breeding birds. La dispersion après la naissance est un processus complexe qui implique des décisions sur quand quitter le territoire natal, comment se déplacer à travers le paysage et où s’établir. Nous avons étudié les facteurs qui déterminent le moment de la dispersion et le recrutement local chez des cincles d’Amérique (Cinclus mexicanus Swainson, 1827) à Chilliwack, Colombie-Britannique. Nous avons suivi 102 jeunes à l’envol provenant de 30 couvées entre 2003 et 2005. La survie jusqu’à 5 jours après l’envol est élevée (>80 %), mais les petits qui prennent leur envol tôt dans la saison ou à un âge plus avancé ont des taux de survie plus grands que ceux qui s’envolent plus tard ou à un âge moins avancé. Cinquante-quatre pourcentage des petits qui survivent à l’envol se dispersent en moins de 14 jours après le départ du nid. Les femelles et les individus qui passent plus de temps à s’alimenter sont plus susceptibles de se disperser en dedans de 14 jours que les mâles et les individus qui s’alimentent moins. Chez ceux qui se dispersent, les individus qui prennent leur envol tôt dans la saison ou à un âge plus avancé passent moins de temps dans leur territoire natal. Nous avons observé qu’environ 10% (10/82) des individus qui se dispersent s’intègrent à la population locale. Le recrutement local des individus qui retardent leur dispersion est plus élevé que le recrutement local des individus qui se dispersent tôt. Notre étude démontre que les bénéfices de fitness associés à une philopatrie natale prolongée ne sont pas restreints aux oiseaux qui se reproduisent de manière coopérative. [ABSTRACT FROM AUTHOR]

The article discusses a study regarding the reproductive success of Lewis's Woodpecker in three habitat types in British Columbia as well as the influence of nesting cavity limitation, competitors, predators and food availability on breeding performance.

• Off the British Columbia coast, a 'Subarctic' zooplankton community is dominant when the Pacific Decadal Oscillation is negative. • In PDO-negative years, Cassin's Auklet diets included more "Subarctic" copepods and less euphausiids. • In ENSO-positive years (El Niño), diets included more larval fish and less copepods-plus-euphausiids. • Nestling auklets grew faster when fed more copepods and less euphausiids, and more copepods-plus-euphausiids and less fish. • Results indicate the importance of 'Subarctic' copepods to predators in the Northern California Current System. Climate-driven variation in the distribution, abundance and phenology of low trophic-level organisms can have cascading effects within marine food webs, and understanding these complex ecosystem dynamics is of vital importance in an age of dramatic environmental change. We tested the hypothesis that marine conditions associated with the state of the Pacific Decadal Oscillation (PDO) exert primary influence on the biogeographic affinities of the zooplankton community, and thus the composition of nestling diets and reproduction of a zooplanktivorous seabird, Cassin's Auklet (Ptychoramphus aleuticus). The 22-year study (1996–2017) took place on Triangle Island, British Columbia, Canada, located at the northern extreme of the California Current System (NCCS) and site of the world's largest breeding colony. Based on annual zooplankton tows in the vicinity of Triangle Island, the biomass of 'Subarctic' zooplankton species (copepods) was elevated in years in which the PDO was in its negative (cold-water) state. The biomass of 'Subarctic' zooplankton was unrelated to both the El Niño-Southern Oscillation (ENSO) and North Pacific Gyre Oscillation (NPGO) indices. Principal Components Analysis (PCA) showed that in those PDO-negative years, diets fed to nestling auklets included more copepod biomass and less euphausiid biomass. Virtually all (>99%) of the copepod biomass consisted of just one species, Neocalanus cristatus, one of the North Pacific Ocean's diagnostic 'Subarctic' copepods. PCA also identified a secondary effect of the El Niño-Southern Oscillation (ENSO) on diets, in that auklet parents delivered more larval fish and less copepods-plus-euphausiids to nestlings in years in which ENSO was in a strongly positive state (i.e., El Niño). The growth rates of nestling auklets, indexed by their mean mass at 25 days of age, was higher in years in which they received more copepods-plus-euphausiids rather than larval fish, and in years in which they received more copepods rather than euphausiids. A previous study in the Central California Current System found that ENSO (to the mid-1990s) and then the NPGO (since the mid-1990s) exerted primary influence on productivity in Cassin's Auklets. In combination, the two studies illustrate how basin-scale climatic processes can non-homogeneously influence productivity in a single species across oceanic domains. For Cassin's Auklet, the contrast can be attributed to latitudinal differences in the prey base (more copepod-based in the north, more euphausiid-based in the south), and linked to ocean transport, temperature, and phenology. This correlational study provides mechanistic insight into ecological functioning in the offshore waters of the NCCS, with application to marine systems elsewhere. We highlight the particular importance of the 'Subarctic' copepods to a zooplanktivorous predator in the NCCS, and the value of seabirds as indicators in this rich marine ecosystem. [ABSTRACT FROM AUTHOR]

Physiological mechanisms underlying migration remain poorly understood, but recent attention has focused on the role of the glucocorticoid hormone corticosterone (CORT) as a key endocrine regulator of migration. The migration-modulation hypothesis (MMH) proposes that baseline plasma CORT levels are elevated in migratory birds to facilitate hyperphagia and lipogenesis and that further elevation of CORT in response to acute stress is suppressed. Consequently, CORT may be a poor indicator of individual condition or environmental variation in migratory birds. We tested the MMH by measuring baseline and stress-induced CORT in common yellowthroats (Geothlypis trichas) during fall migration over 2 consecutive years in the Revelstoke Reach drawdown zone, a migratory stopover site affected by local hydroelectric operations. Birds had low baseline CORT at initial capture (<5 ng/mL) and then showed a robust stress response, with CORT increasing to ca. 50 ng/mL within 10-20 min. Our data therefore do not support the MMH. Baseline CORT did not vary with body mass, time of capture, Julian day, or year, suggesting that variable flooding regimes did not affect baseline CORT. Individual variation in the rate of increase in CORT was correlated with Julian day, being higher later in the migration period. Our data suggest that plasma CORT can be a useful metric in migration studies.