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Migratory birds must make complex decisions to use wind to their advantage during flight and increasing flight performance is particularly important while crossing ecological barriers. Age-related differences in how birds deal with wind have suggested experience improves necessary skills in gaining positive wind support. However, differences in wind support between age groups over ecological barriers have rarely been tested, and our understanding of how birds acquire related skills is lacking. We compared wind support achieved by adult and subadult Caspian terns, Hydroprogne caspia, during southward and northward crossings of the Sahara Desert by quantifying air-to-groundspeed ratios (AGR). We also tested possible underlying causes of lower subadult wind support in comparison to adults by calculating optimal AGR altitudes and fitting step selection functions in response to wind direction and speed. We found no difference between age groups in autumn, when young were flying with adults, but subadults had lower wind support during their first solo northward crossings. Adults departed northwards from wintering areas earlier in the year and encountered more favourable wind conditions than subadults, yet both age groups made similar movement decisions in relation to wind. Consequently, differences in performance are better explained by timing of passage rather than movement skills. Our findings highlight the influence of wind seasonality over the Sahara on migratory behaviour and raise questions about the evolution and ontogeny of migratory timing in relation to wind patterns and other factors that may determine departure decisions.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/lice nses/by-nc-nd/4.0/).

Philopatry and monogamy are conventionally viewed as strategies for improving fitness. Many philopatric and monogamous species have, however, been shown to perform breeding dispersal—an exchange of territory (and often also partner) between two breeding seasons. The adaptiveness of breeding dispersal remains controversial, as data remain scarce and sporadic. For the Northern Goshawk, a typically highly philopatric and monogamous forest raptor, pairs breeding in barren forest landscapes produce fewer fledglings than pairs breeding in more productive landscapes. Using data on Finnish breeding female Goshawks (Accipiter gentilis) during 1999–2016, we tested the hypotheses that: (1) breeding dispersal is more likely at barren territories, (2) dispersing females move to less barren territories, and (3) breeding dispersal improves the survival of young. About 29% of the female Goshawks in our study performed breeding dispersal, which contrasts to philopatry and suggest that site and partner fidelities show large variation within the species’ breeding range. We found no evidence that territorial landscape barrenness (proxy on habitat quality) affects the probability of breeding dispersal. However, females that dispersed upgraded to less barren territories. Nevertheless, there were no subsequent effects of breeding dispersal on reproductive performance, suggesting no obvious difference in the capability of rearing young at either site. Although dispersal events were directed to less barren habitats, we suggest that female dispersal is not driven by the pursue for more prospersous habitats, rather that those females are forced to move, for whatever reason. In addition to other observed reasons such as female–female competition for mates and loss of the original mate, intense logging of mature forests lowering local food availability and restricting nest site availability were likely a partial cause of increased breeding dispersal.

While advances in biologging have revealed many spectacular animal migrations, it remains poorly understood how young animals learn to migrate. Even in social species, it is unclear how migratory skills are transmitted from one generation to another and what implications this may have. Here we show that in Caspian terns Hydroprogne caspia family groups, genetic and foster male parents carry the main responsibility for migrating with young. During migration, young birds stayed close to an adult at all times, with the bond dissipating on the wintering grounds. Solo-migrating adults migrated faster than did adults accompanying young. Four young that lost contact with their parent at an early stage of migration all died. During their first solo migration, subadult terns remained faithful to routes they took with their parents as young. Our results provide evidence for cultural inheritance of migration knowledge in a long-distance bird migrant and show that sex-biased (allo)parental care en route shapes migration through social learning.

Sex and age segregation on the non-breeding grounds is common in raptor species. We studied the European Honey Buzzard (Pernis apivorus) on its southern African non-breeding grounds to examine changes in sex and age ratios over a period of recent population expansion (2002–2017). Photographs from multiple open sources were analysed. The adult population was found to be overwhelmingly female (93.3%) with no significant variation over months, years, or latitudes. This supports the arrival-time hypothesis, which states that the sex responsible for establishing the breeding territory (the male in honey buzzard) will spend the non-breeding period closest to the breeding grounds, allowing them to reduce intrasexual competition for breeding territories. Juvenile and second year birds (41.6% of the population) were more common at lower elevations, as well as further south in the sub-region. This is likely due to a funnelling effect of inexperienced juvenile birds further south and to coastal zones. In addition, juvenile birds do not return to the breeding grounds for at least 2 years, so may be more likely to migrate further south. Finally, second year birds increase later in the austral summer. This may be a result of both juvenile birds moulting into more adult plumage, and a southward intra-continental movement of young honey buzzards in Africa.

AIM: Long‐distance Palaearctic migrant birds are declining at a faster rate than short‐distance migrant or resident species. This is often attributed to changes on their non‐breeding grounds and along their migratory routes. The European honey buzzard (Pernis apivorus) is a scarce migrant in southern Africa that is declining globally. This study assessed the distribution and abundance of honey buzzards in southern Africa over the past four decades and compared it to trends in the East African population to examine possible drivers of population expansion in southern Africa. LOCATION: Southern and East Africa. METHODS: European honey buzzard reporting data were collected from a variety of sources including citizen science databases (1983–2017). In addition, records of all other southern African vagrants (including ten other regularly occurring species) were gathered to account for changes in birdwatching effort in the subregion. To assess the effect of forest loss on honey buzzard abundance, rolling correlations were performed using forest cover in East Africa and number of honey buzzard records in both subregions. RESULTS: European honey buzzard records in southern Africa have increased over five times more than other regularly occurring vagrant species and almost 40 times more than honey buzzard in Tanzania, where the population has remained stable. Loss of forested area in East Africa was correlated with an increase in European honey buzzard records in southern Africa. MAIN CONCLUSIONS: We suggest that the European honey buzzard shift in wintering range may be driven by a decline in suitable habitat further north in Africa amongst other possible reasons. This effect may have been amplified by an increase in appropriate habitat across southern Africa brought about by anthropogenic changes to vegetation such as increased tree cover in urban areas. This study further highlights the importance of using African distributional data banks to understand the effects of global change on Palaearctic migrant bird species.

Habitat preferences and foraging strategies affect population-level space use and are therefore crucial to understanding population change and implementing spatial conservation and management actions. We investigated the breeding season habitat preference and foraging site fidelity of the under-studied and threatened, Baltic Sea population of Caspian Terns (Hydroprogne caspia). Using GPS devices, we tracked 20 adult individuals at two breeding colonies, in Sweden and Finland, from late incubation through chick-rearing. Analyzing foraging movements during this period, we describe trip characteristics for each colony, daily metrics of effort, habitat use, and foraging site fidelity. We found that daily time spent away from the colony increased throughout the season, with colony-level differences in terms of distance travelled per day. In general, terns selected shallow waters between 0–5 meters in depth with certain individuals using inland lakes for foraging. We show, for the first time, that individual Caspian Terns are faithful to foraging sites throughout the breeding season, and that individuals are highly repeatable in their strategies regarding foraging site fidelity. These results fill important knowledge gaps for this at-risk population, and extend our general knowledge of the breeding season foraging ecology of this widespread species.

Decreases in suitable habitat due to loss and fragmentation on the African non-breeding grounds are believed to be a driver of the declines in Palaearctic migrants. However, the effects of habitat loss and fragmentation on individual migrants have rarely been investigated. The European Honey-buzzard Pernis apivorus, a migratory forest specialist, displays the characteristics of a species that would be sensitive to declines in suitable habitat. We assessed site fidelity, habitat selection and home range characteristics of 32 tracked European Honey-buzzards in Africa to understand how habitat transformation on the non-breeding grounds affects the movement behaviour (particularly habitat use and home range characteristics) of the species. Adults had greater site fidelity than juveniles, indicating that young birds were exploring to locate suitable habitat for future non-breeding territories. Besides site fidelity, there were few significant differences between the movements of adult and juvenile Honey-buzzards. Birds of all age classes strongly selected treed habitat, as expected. Treed largest patch index and edge density had a negative effect on home range size, demonstrating that Honey-buzzards rely on large tracts of continuous forest, but can tolerate some level of fragmentation. Individuals with larger home ranges due to greater levels of forest fragmentation moved greater daily distances. In addition, Honey-buzzards spent more time in home ranges with larger treed largest patch indices and lower edge density. This reveals that birds that do not have access to a large patch of unfragmented forest are both flying greater distances on a daily basis and moving to new home ranges more often. This likely results in greater energy expenditure over their non-breeding period, which may have adverse effects on their long-term survival. Furthermore, our analyses support the hypothesis that continuing forest loss in Africa will have a negative effect on the European Honey-buzzard population.

Thermal soaring birds extract energy from the atmosphere to achieve energetically low-cost movement. When encountering regions that are energetically costly to fly over, such as open seas, they should attempt to adjust the spatiotemporal pattern of their passage to maximize energy extraction from the atmosphere over these ecological barriers. We applied the concept of energy landscapes to investigate the spatio-temporal dynamics of energy availability over the open sea for soaring flight. We specifically investigated how the ‘energy seascape’ may shape age-specific sea-crossing behaviour of European honey buzzards, Pernis apivorus, over the Mediterranean Sea in autumn. We found uplift potential over the sea to be the main determinant of sea-crossing distance, rather than wind conditions. Considering this variable as a proxy for available energy over the sea, we constructed the energy seascape for the autumn migration season using 40 years of temperature data. Our results indicate that early-migrating adult buzzards are likely to encounter adverse energy subsidence over the Mediterranean, whereas late-migrating juveniles face less adverse flight conditions, and even conditions conducive to soaring flight. Our study provides evidence that the dynamics of the energy landscape can explain intra-specific variation in migratory behaviour also at sea.

Given the limited resources available for conservation, it is important that the areas to preserve are selected in a cost effective manner. However, the cost effectiveness of the surrogate species strategy (the use of information on one or more species to identify areas of value for other species for which there is no, or more limited, available information) has seldom been evaluated. In this study, we investigate the opportunity cost of setting aside breeding sites of two forest raptor species (the surrogate species) by evaluating their individual and combined contribution to preserve diversity of polypores (wood-decaying fungi) and birds against the contributions of previously established nature reserves. We use numeric optimization models to compare different reserve selection strategies. Site selection based on nest sites of the dominant raptor species was more cost-effective than strategies using sites of the subordinate species or those processes previously used to select nature reserves in Finland. The inclusion of both raptor species in the reserve selection model further improved its performance relative to other approaches. This indicates that the means by which Finnish reserves are selected could be enhanced by including the breeding sites of these, and maybe other species, among the criteria used to select reserves in the future. These results show that information on charismatic and well-surveyed species could be a cost-efficient add-on to help enhance conservation endeavours. Where there is inter-specific competition for biodiverse sites, and using multiple species is costly, basing reserve selection primarily on breeding sites of a dominant species may be the best strategy. However, further work is required to establish the extent to which dominant species are typically better indicators of conservation relevance.

The evidence of negative impacts of agricultural pesticides on non-target organisms is constantly growing. One of the most widely used group of pesticides are neonicotinoids, used in treatments of various plants, e.g. oilseed crops, corn and apples, to prevent crop damage by agricultural insect pests. Treatment effects have been found to spill over to non-target insects, such as bees, and more recently also to other animal groups, among them passerine birds. Very little is known, however, on the presence of neonicotinoids in other wild species at higher trophic levels. We present results on the presence of neonicotinoid residues in blood samples of a long-distant migratory food-specialist raptor, the European honey buzzard. Further, we investigate the spatial relationship between neonicotinoid residue prevalence in honey buzzards with that of crop fields where neonicotinoids are typically used. A majority of all blood samples contained neonicotinoids, thiacloprid accounting for most of the prevalence. While neonicotinoid residues were detected in both adults and nestlings, the methodological limit of quantification was exceeded only in nestlings. Neonicotinoids were present in all sampled nests. Neonicotinoid presence in honey buzzard nestlings' blood matched spatially with the presence of oilseed plant fields. These are the first observations of neonicotinoids in a diurnal raptor. For better understanding the potential negative sublethal of neonicotinoids in wild vertebrates, new (experimental) studies are needed. (c) 2018 The Authors. Published by Elsevier B.V.

Contemporary tracking studies reveal that low migratory connectivity between breeding and non-breeding ranges is common in migrant landbirds. It is unclear, however, how internal factors and early-life experiences of individual migrants shape the development of their migration routes and concomitant population-level non-breeding distributions. Stochastic wind conditions and geography may determine whether and where migrants end up by the end of their journey. We tested this hypothesis by satellite-tagging 31 fledgling honey buzzards Pernis apivorus from southern Finland and used a global atmospheric reanalysis model to estimate the wind conditions they encountered on their first outbound migration. Migration routes diverged rapidly upon departure and the birds eventually spread out across 3340 km of longitude. Using linear regression models, we show that the birds' longitudinal speeds were strongly affected by zonal wind speed, and negatively affected by latitudinal wind, with significant but minor differences between individuals. Eventually, 49% of variability in the birds' total longitudinal displacements was accounted for by wind conditions on migration. Some birds circumvented the Baltic Sea via Scandinavia or engaged in unusual downwind movements over the Mediterranean, which also affected the longitude at which these individuals arrived in sub-Saharan Africa. To understand why adult migrants use the migration routes and non-breeding sites they use, we must take into account the way in which wind conditions moulded their very first journeys. Our results present some of the first evidence into the mechanisms through which low migratory connectivity emerges.

Summary With biodiversity facing threats, there is a need to improve reserve selection procedures. However, detailed information about different biodiversity measures (e.g. species richness) at potential sites is often lacking, and selecting areas that protect most biodiversity is difficult. To simplify matters, biodiversity surrogate species, that is, species associated with higher biodiversity than average, have been used for area selection. However, consensus about the performance of the surrogate species concept is lacking, and there are few studies investigating potential differences in the effectiveness of multiple predators as surrogates for biodiversity over large spatial scales. We evaluated two avian predators, the northern goshawk Accipiter gentilis and the Ural owl Strix uralensis, as surrogates for biodiversity in the boreal forest biome in Western Finland. We used a study design including nest sites and two reference sites for each nest, the diversity of birds and wood-decaying fungi (polypores). We assessed simultaneously whether surrogacy persisted at the landscape level while moving from one vegetation zone to another. We generally found more birds and polypores around the nest sites for both goshawks and Ural owls than at their respective reference sites. However, the goshawk outperformed the Ural owl. Additionally, although biodiversity was found to decrease at the landscape scale as a result of a decrease in vegetation complexity with increasing longitude, the surrogacy efficiency of the raptors remained unchanged. Synthesis and applications. These findings suggest that the surrogate species concept applied to raptors may be an efficient addition to methods for identifying areas of conservation priority, even across vegetation zones. We conclude that protecting areas around raptor nests is a method to consider in order to halt forest biodiversity loss. Finally, sampling biodiversity along diversity and landscape gradients can improve the necessary assessment of surrogate species.

Different prey species can vary in their significance to a particular predator. In the simplest case, the total available density or biomass of a guild of several prey species might be most relevant to the predator, but behavioural and ecological traits of different prey species can alter the picture. We studied the population dynamics of a predator-prey setting in Finland by fitting first-order log-linear vector autoregressive models to long-term count data from active breeding sites of the northern goshawk (Accipiter gentilis; 1986-2009), and to three of its main prey species (1983-2010): hazel grouse (Bonasa bonasia), black grouse (Tetrao tetrix) and capercaillie (T. urogallus), which belong to the same forest grouse guild and show synchronous fluctuations. Our focus was on modelling the relative significance of prey species and estimating the tightness of predator-prey coupling in order to explain the observed population dynamics, simultaneously accounting for effects of density dependence, winter severity and spatial correlation. We established nine competing candidate models, where different combinations of grouse species affect goshawk dynamics with lags of 1-3 years. Effects of goshawk on grouse were investigated using one model for each grouse species. The most parsimonious model for goshawk indicated separate density effects of hazel grouse and black grouse, and different effects with lags of 1 and 3 years. Capercaillie showed no effects on goshawk populations, while the effect of goshawk on grouse was clearly negative only in capercaillie. Winter severity had significant adverse effects on goshawk and hazel grouse populations. In combination, large-scale goshawk-grouse population dynamics are coupled, but there are no clear mutual effects for any of the individual guild members. In a broader context, our study suggests that pooling data on closely related, synchronously fluctuating prey species can result in the loss of relevant information, rather than increased model parsimony.

Predators impose strong selection on their prey, regulate prey populations and engage in coevolutionary interactions with their prey. The intensity of selection and the strength of coevolutionary interactions will depend on how stringent predators are in their choice of prey. We estimated susceptibility of different species of birds to predation by two common raptors, the northern goshawk Accipiter gentilis and the Eurasian sparrowhawk A. nisus, in an agricultural landscape in Denmark and boreal forests in Finland. We estimated susceptibility to predation as the deviation of the log10-transformed observed frequency of prey of different species from the log10-transformed expectation based on population density during the breeding season. We found a high degree of consistency in susceptibility to predation by the goshawk in two areas in Finland. More importantly, there was significant consistency in susceptibility to predation between Denmark and Finland, albeit the degree of consistency in the goshawk was higher than in the sparrowhawk. There was considerable overlap in susceptibility to predation between goshawk and sparrowhawk in Denmark, but not in Finland, implying differences in intensity of interspecific competition as reflected by a much higher extent of goshawk predation on sparrowhawks in Denmark than in Finland. Our findings suggest that hawks impose similar selection pressures on their prey populations, and that the degree of consistency has implications for intensity of interspecific killing.

Parental food provisioning and sibling rivalry have inspired abundant investigations of evolutionary conflicts within families. Nevertheless, their joint effects have seldom been assessed in relation to parental and environmental state. We investigated state dependency of feeding behaviors through the complete nesting phase in a species whose young both partly beg for food and partly self-feed, the northern goshawk Accipiter gentilis. After hatching, when young relied on being fed beak-to-beak, siblings achieved equal amounts of food irrespective of hatching rank, body condition, and sex. However, mothers new to a territory fed their offspring less than experienced ones independently of food availability. This pattern persisted also after nestlings grew and initiated to self-feed and aggressively monopolize prey. Mothers never interfered with aggressions but stayed with their even feeding strategy paying little attention to begging activity. Although mothers’ even feeding strategy is likely to equalize siblings’ survival probabilities when food is abundant, the fact that nestlings in good condition monopolize prey in self-feeding situations will boost brood asymmetries when food decreases. Because new mothers feed their offspring less than experienced ones, aggressive sibling rivalry will be particularly crucial among mothers lacking previous local breeding experience. Albeit hitherto overlooked, feeding behaviors constitute important mechanisms explaining experience-related differences in reproductive performance of wild animals. Key words: begging behavior, experience-dependent fecundity, food availability, parent‐offspring conflict, parental breeding experience, sibling competition. [Behav Ecol]

Current climate change has been found to advance spring arrival and breeding dates of birds, but the effects on autumn migration and possible responses in the distribution of wintering individuals are poorly known. To thoroughly understand the consequences of climate change for animal life histories and populations, exploration of whole annual cycles are needed. We studied timing of migration (years 1979-2007), breeding phenology (1979-2007) and breeding success (1973-2007) of Eurasian sparrowhawks Accipiter nisus in Finland. We also investigated whether the migration distance of Finnish sparrowhawks has changed since the 1960s, using ringing recovery records. Since the late 1970s Finnish sparrowhawks have advanced their spring arrival, breeding and autumn departure considerably, but the migration distance has not changed. Early migrants, who are the ones with the highest reproductive success, show the strongest advance in the timing of spring migration. In autumn, advanced departure concerns young sparrowhawks. Late autumn migrants, who are mainly adults, have not advanced their migration significantly. The sparrowhawk is the most common bird of prey and the main predator of most passerines in Finland. Therefore, changes in sparrowhawk migration phenology may affect the migration behaviour of many prey species. The breeding success of sparrowhawks has increased significantly over the study period. This is however more likely caused by other factors than climate change, such as reduced exposure to organochlorine pollutants.

The ongoing climate change has improved our understanding of how climate affects the reproduction of animals. However, the interaction between food availability and climate on breeding has rarely been examined. While it has been shown that breeding of boreal birds of prey is first and foremost determined by prey abundance, little information exists on how climatic conditions influence this relationship. We studied the joint effects of main prey abundance and ambient weather on timing of breeding and reproductive success of two smaller (pygmy owl Glaucidium passerinum and Tengmalm's owl Aegolius funereus) and two larger (tawny owl Strix aluco and Ural owl Strix uralensis) avian predator species using long-term nation-wide datasets during 1973-2004. We found no temporal trend either in vole abundance or in hatching date and brood size of any studied owl species. In the larger species, increasing late winter or early spring temperature advanced breeding at least as much as did high autumn abundance of prey (voles). Furthermore, increasing snow depth delayed breeding of the largest species (Ural owl), presumably by reducing the availability of voles. Brood size was strongly determined by spring vole abundance in all four owl species. These results show that climate directly affects the breeding performance of vole-eating boreal avian predators much more than previously thought. According to earlier studies, small-sized species should advance their breeding more than larger species in response to increasing temperature. However, we found an opposite pattern, with larger species being more sensitive to temperature. We argue that this pattern is caused by a difference in the breeding tactics of larger mostly capital breeding and smaller mostly income breeding owl species.

A changing climate induces shifts in the location of biomes. Tracing such a shift may pose problems for life history traits adapted to the prior conditions, so that, e.g. the timing of reproduction and the time with sufficient resources for rearing hatchlings do not match. We show that the timing of breeding of Finnish common buzzards Buteo buteo, has advanced with over ten days as a response to the warming of early spring, during 1979―2004. During the same period the isoclines of the onset of breeding have moved about 200 km to the north-east. However, the reproductive performance of the common buzzard has not increased as a response to these changes. Despite increasing temperatures during early spring, the temperatures of early summer have remained the same since the 1970s. Combined, the early onset of breeding and the unchanged temperatures of early summer have lead to decreased post-hatching temperatures. Under these circumstances, common buzzard offspring now face a higher risk to hatch into less favourable weather conditions than three decades ago. Furthermore, summer precipitation, harmful for nestlings, has been predicted to increase in the future, thus possibly further worsening the circumstances for breeding common buzzards. Our results demonstrate that even if common buzzards in Finland breed at the northern limit of the species' distribution, and could therefore be expected to gain advantage from a warming climate, the opposite is the case.

Food supplementation experiments have been widely used to get detailed insight into how food supply contributes to the reproductive performance of wild animals. Surprisingly, even though food seldom is distributed evenly in space, variation in local habitat quality has usually not been controlled for in food supplementation studies. With results from a two-year feeding experiment involving a habitat-sensitive avian top predator, the Northern Goshawk Accipiter gentilis, we show that treatment effects on goshawk reproductive performance are habitat dependent. Extra food reduced nestling mortality in low-quality territories where prime habitat (forest) is scarce, but not in high-quality territories where prime habitat is abundant. Consequently, brood size did not differ between treatment categories in heavily forested territories, but fledgling numbers differed between unfed and fed goshawk pairs breeding in territories where forest is scarce. However, because extra food was not superabundant, this artificial increase in offspring number induced a dramatic decrease in nestling condition in low-quality territories. Treatment effects were detected even after controlling statistically for other potentially confounding effects (year, territory identity) and strongly covaried with territory-specific abundances of the most important summer prey species. These results highlight the importance of acknowledging the effect that small-scale variation in habitat quality and availability of natural food may have on the results of food supplementation experiments. In order to assess the generality of food supplementation effects, the integration of habitat heterogeneity and variation in food abundance is thus needed, especially among species in which small-scale variation in habitat quality influences demographic patterns.

Habitat composition is an important factor influencing nesting failure probability in birds. However, although various habitat effects such as fragmentation and edge density are known to have clear negative effects on the breeding success of passerines, the role that habitat composition plays in shaping nesting failure patterns among other avian groups is less well known. We studied nesting failure in a large forest raptor, the Northern Goshawk Accipiter gentilis, during the period 1999–2003 in Finland. Illegal human persecution was found to constitute a major cause of failure among nests where cause could be determined accurately (comprising c. 60% of all failed nesting attempts). Egg predation by corvids and nestling predation by Eagle Owls Bubo bubo were also common. However, the exact cause of nesting failure could not be inferred in every case. Overall, the degree of initial parental investment (clutch size and egg volume) was significantly smaller in nests that failed than in nesting attempts that were successful. This did not apply to nests that were destroyed by humans, in which investment was at a level equal to nests that were successful. Although the probability that a nesting attempt would fail was also related to small-scale nest concealment, nesting failure probability was not associated with main prey density or several measures describing territorial habitat composition at larger scales. Small initial parental investment, not habitat composition, is thus the major correlate of nesting failure in Goshawks.

Summary 1 Habitat heterogeneity has important repercussions for species abundance, demography and life-history patterns. While habitat effects have been more thoroughly studied in top-down situations (e.g. in association with predation), their role in bottom-up situations (e.g. in association with food abundance) has been less explored and the underlying mechanism(s) behind the ecological patterns have not commonly been identified. 2 With material from 1993 to 2003, we test the hypothesis that the reproduction of Finnish northern goshawks Accipiter gentilis (L.) is bottom-up limited by habitat composition, especially in situations where the density of their main prey (grouse) is low. Special emphasis was placed on identifying the mechanism(s) behind potential habitat effects. 3 While laying date and large-scale variation in the main prey density (but not habitat composition) were related to the number of eggs goshawks laid, small-scale differences in alternative prey density between different territories later influenced how many young were fledged via the mechanism of habitat-dependent partial-brood loss. As a result of this mechanism, a difference in nestling condition also arose between goshawk territories with differing habitat compositions. 4 As the relative proportions of different landscape elements in a given landscape is a function of large-scale differences in geomorphology and land use, this means that the reproductive performance of goshawks as averaged over larger scales can be understood correctly only in respect to the fact that habitat gradients differ across landscapes. 5 In addition to being one of the first papers identifying the mechanism of partial brood loss as being primarily responsible for the habitat-specific differences in the production of young, this study further illustrates the need to identify small-scale mechanisms to correctly understand the large-scale patterns of reproductive performance in territorial species. The repercussions of the observed habitat effect for local population development are discussed.

Summary 1. Local population studies have shown that sex allocation among many birds and mammals seems to be partly non-random and in connection to surrounding factors, such as environmental or parental quality. In this scenario, if environmental quality varies in space and time, it is feasible that environmental quality also comes to influence offspring sex ratio on larger geographical scales. 2. Investigating this idea - using nation-wide data sets on size-dimorphic Finnish northern goshawks Accipiter gentilis from 1989 to 1998 - we found that offspring sex ratio is related to spatial and temporal variation in availability of their main prey, woodland grouse species. 3. In a majority of locations ( n = 73), broods are large and male-biased when grouse density is high, while small and female-biased broods are found in areas and times with low grouse density. When adjusted for grouse density, the correlation between brood size and sex ratio disappears, but the correlation between grouse density and sex ratio remains. 4. We also found evidence indicating a mechanism balancing local offspring sex ratios towards the previously rarer sex with a time lag of 1 year. That is, local sex ratios in subsequent years are negatively correlated. 5. Our study highlights the importance of inclusion of both time and space in sex ratio studies. Ignorance of these dimensions could explain a great deal of the inconsistency in many earlier local sex ratio studies. 6. Irrespective of whether the observed pattern is the result of facultative manipulation, sex biased mortality, or both, it is suggested that the male-biased sex ratio during periods of high grouse availability maximizes goshawk reproductive success.

While much effort has been made to quantify how landscape composition influences the distribution of species, the possibility that geographical differences in species interactions might affect species distributions has received less attention. Investigating a predator-prey setting in a boreal forest ecosystem, we empirically show that large-scale differences in the predator community structure and small-scale competitive exclusion among predators affect the local distribution of a threatened forest specialist more than does landscape composition. Consequently, even though the landscape parameters affecting Siberian flying squirrel (Pteromys volans) distribution (prey) did not differ between nest sites of the predators Northern Goshawks (Accipiter gentilis) and Ural Owls (Strix uralensis), flying squirrels were heterospecifically attracted by goshawks in a region where both predator species were present. No such effect was found in another region where Ural Owls were absent. These results provide evidence that differences in species interactions over large spatial scales may be a major force influencing the distribution and abundance patterns of species. On the basis of these findings, we suspect that subtle species interactions might be a central reason why landscape models constructed to predict species distributions often fail when applied to wider geographical scales.

Contemporary research has documented a large number of shifts in spring phenology and changes in distribution range although the average spring temperatures have increased by only 0.3–0.6 °C over the past 100 years. Generally, earlier breeding birds have larger clutch sizes, and the advancing spring could thus potentially increase breeding success. Shifts in spring phenology can, however, be crucial for bird reproduction, and mistiming the breeding event may even have negative consequences for population development. Our aim was to explore how weather and prey abundance relates to the breeding performance of a north European top predator, the northern goshawk Accipiter gentilis. Our nationwide dataset from Finland, spanning the period 1989–2004, shows that ambient weather has a greater impact on the timing and success of breeding than the density of grouse Tetraonidae, the main prey of goshawks. Higher early spring temperatures were associated with advancing hatching date of goshawks. Correspondingly, grouse density and temperature during laying and brooding were positively associated with brood size, while precipitation showed a negative connection. Applying our models to a future scenario of climate warming, combined with a 50 % reduction in grouse density, suggests that average breeding dates will advance only 2.5 days and average breeding success would remain the same. Notably, breeding success was not spatially equal throughout Finland, as northern and eastern populations suffered most from declining grouse densities. The observed pattern is thus the opposite to what is expected from a population situated at the northern edge of its distribution range, and thus may help to understand why populations may not increase at the northern edge of their thermal distribution due to climate change.

Environmental quality has the potential to influence dispersal if cost of dispersing is outweighed by cost of staying. In that scenario, individuals experiencing different conditions in their natal area are expected to differ in their dispersal. Even if there is wide agreement that reasons behind the dispersal decision are multiple, it is often less clear what conditions actually add to the observed dispersal behavior. The scale at which the dispersal behavior is analyzed can also be of crucial importance for a correct understanding of the dispersal process. Furthermore, in long-lived species factors influencing dispersal behavior of juveniles may differ from those adding to dispersal of adults. Using 12 years of banding data (1989–2000), we studied dispersal behavior of Northern Goshawks (Accipiter gentilis) hatched over a wide area in Finland in relation to local demographic and ecological conditions. Hatching rank and hatching date added to the probability of leaving in the first place; wherea...

Using nationwide long-term data on goshawk and grouse populations in Finland we study the spatial dynamics of the numbers of breeding northern goshawk (Accipiter gentilis) pairs, goshawk brood size and offspring sex ratio and their connection to the abundance of grouse. Our first large-scale data comprise of observations on goshawk nests during 1986–2001 pooled to 21 different regions. The second set are annual (1989–1998) observations of brood size and offspring sex ratio (females over the sum of females and males) in goshawk nests all over the country, aggregated to 50 km grid level (n =28 grid units). The third set comprises counts (1989–2001) of four species of woodland grouse, split to adults and juveniles, also given in the same 50 km grid units. Using these data, we show that the annual numbers of northern goshawk nests in the different regions fluctuate in synchrony. Synchrony is also found in long-term fluctuations of northern goshawk brood size and offspring sex ratio. Moreover, synchrony is found in annual numbers of grouse juveniles and adults, the main prey for the northern goshawk. In the brood size and offspring sex ratio of the goshawk, as well as in the annual numbers of grouse juveniles and adults the degree of synchrony falls off with increasing distance. However, only in sex ratios and in grouse dynamics are the slopes of synchrony vs distance roughly matching. We also found that sex ratio either vs grouse juveniles or grouse adults has a more matching spatial dimension (50 km radius) that sex ratio vs brood size. These observation lend support to the hypothesis that goshawk offspring sex ratio and grouse abundance are interconnected. Despite the reason, consequences of spatial coupling in sex ratio could have repercussions on other life history events.

In many populations of size dimorphic birds, brood sex ratios change with advancing laying date. The slopes of these trends, however, vary in time and space, both between and within species. We studied brood sex ratios (proportion of males) of northern goshawks Accipiter gentilis in Finland in relation to laying date using ringing data from 1989 to 1998. At the nationwide scale, i.e. the whole of Finland, between-year variation in offspring sex ratio was moderate, and the sex ratio did not change with later laying date. At a regional scale, the sex ratio was seasonally constant in one region but decreased in another, although the laying-date/brood-size relationship was identical. Hence, the size and sex composition of goshawk broods are locally two uncoupled facets of reproduction. Both the national and regional patterns differ drastically from the pattern of a Dutch population, where sex ratio increased seasonally. We suggest that spatial variation in inter-annual seasonal sex-ratio trends might be indicative of the scale at which sex-ratio feedback functions. The sex ratio of breeders is a factor that could add to the understanding of the observed geographical differences in seasonal sex-ratio patterns.