Search

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.

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.

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.

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]

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.