Delayed numerical response of goshawks to population fluctuations of forest grouse

Delayed density-dependent mortality induced by delayed numerical response of predators can drive prey populations to fluctuate in high-amplitude cycles. We studied numerical response of goshawks Accipiter gentilis to varying densities of their main prey (forest grouse) in western Finland during 1979–1996. Occupancy rate of goshawk territories tracked grouse numbers with a two year lag. Occupancy rate of goshawk territories and pooled number of adult and young goshawks correlated negatively with a 1–2 year lag to the chick production of grouse. Goshawk to grouse ratio was negatively related to grouse density. This suggests that goshawk predation on grouse is inversely dependent on grouse density. We conclude that in northern Europe with few alternative preys, goshawk predation might contribute to the generation of multiannual cycles of forest grouse. This should be tested experimentally.     

Scale and seasonal sex-ratio trends in northern goshawk Accipiter gentilis broods

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.     

Brood sex ratio varies with diet composition in a generalist raptor

While sex allocation has been investigated productively at both population and family levels, as yet no general theory has been developed that is capable of linking processes at these two ecological scales, and very few empirical studies have examined cross‐scale patterns. In Finnish northern goshawks (Accipiter gentilis), nestling sex ratio of local subpopulations is related to the spatial and temporal variation in the abundance of their principal avian prey, woodland grouse. Using data from an urban breeding population in Hamburg, Germany, I investigated: (1) whether brood sex ratio of goshawks varies with diet composition at the family level; (2) whether such variation could reflect adaptive adjustment; and (3) how family‐level allocation can drive population‐level patterns, such as those observed in Finland. Feral pigeons (Columba livia) were the most important prey species, with a pooled contribution to total diet of 36%. Brood sex ratio varied significantly with the proportion of pigeons in the breeding‐season diet of pairs (increasing male bias). However, there was no evidence for sex‐differential effects of diet composition, so it remains unclear whether the observed sex‐ratio variation was an adaptive response. As all study pairs inhabited an (urban) environment where pigeons were unusually abundant, family‐level sex‐ratio adjustment caused a marked male bias in offspring sex ratio at the population level (male‐biased nestling sex ratio in four of five years; pooled data: 60% males). This suggests that the large‐scale variation observed in Finnish goshawk populations mirrors sex‐ratio adjustment shown by individual families in response to small‐scale environmental conditions. Apart from linking patterns empirically across ecological scales, this study is, to my knowledge, the first to demonstrate that family‐level brood sex ratio varies with realized resource use (diet composition) in a raptor species. Previous studies either failed to find significant associations or, more commonly, violated theoretical assumptions by measuring environmental prey abundance (often integrated over large areas) rather than realized prey use of individual breeding pairs. I conducted a meta‐analysis of offspring sex‐ratio data from 17 goshawk populations across Europe to put my results into perspective. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 937–951.     

花尾榛鸡的非对称性比和成体存活率

1999至2002年,在法国东南部的阿尔卑斯山,通过无线电追踪方法研究了花尾榛鸡的性比问题。首先,我们通过直接观测无线电标记雄性的配对比例,在消除可能的捕捉误差后,发现繁殖种群性比为1．26（即未配对的雄性占21％）。然后,我们估计了标记个体的存活率和繁殖成功率。在假设窝扩散时幼体的性比平衡的前提下,通过两性和两个年龄组（幼体,〈10月龄的个体;成体〉10月龄的个体）的确定性统计模型,得到的理论性比为1．22（即未配对的雄性占18％）,这一结果与实际观测的性比十分接近。我们认为,雌性死亡率高导致的两性存活率差异可以解释雄性性比偏高现象。我们进而讨论了花尾榛鸡整个分布区内居间强度的非对称性比的适应意义,以及在衰退的花尾榛鸡种群中雌性数量极端不足的后果[动物学报52（4）：655—662,2006]。     

Predator control and the density and reproductive success of grouse populations in Finland

The impact of predator removal or protection on the reproductive success and density of grouse populations was studied experimentally in southern and northern Finland. In predator removal areas small and medium-sized carnivores wore efficiently hunted, while in predator protection areas hunting was prohibited. Both predator (red fox, raccoon dog, pine marten and stoat) and grouse populations were monitored. The breeding success of grouse, indicated by the young/adults ratio, decreased in the predator protection area in northern Finland during a vole low. Despite a decline in the vole population, the breeding success of grouse did not decline in the predator removal area. The mean brood size during the experiment was significantly higher in the removal areas than in the protection areas both in southern and northern Finland. Predator removal/protection thus affected the reproductive success of grouse, but the impact of control on adult grouse populations was not as evident.     

Patterns in grouse and Woodcock Scolopax rusticola hunting yields from central Norway 1901–24 do not support the alternative prey hypothesis for grouse cycles

According to the alternative prey hypothesis, autumn populations of ground-nesting game birds fluctuate in synchrony with vole numbers because generalist predators that mainly eat voles switch to alternative prey, such as eggs and chicks, when vole numbers decline. In hunting statistics from Nord-Trøndelag, central Norway, 1901–24, annual fluctuations in the number of Willow Grouse Lagopus lagopus and Western Capercaillie Tetrao urogallus , but not of Woodcock Scolopax rusticola , were positively related to vole numbers in the current year. Both Woodcock and grouse indices were related to hunting indices of Goshawk Accipiter gentilis and to weather variables assumed to influence the birds' survival or reproduction, suggesting that the indices actually reflected local population levels. Synchronous vole and grouse fluctuations are consistent with the alternative prey hypothesis (although predator densities were low in the early 1900s), but the asynchronous Woodcock fluctuations refute the hypothesis. Rather, because the Woodcock does not feed on plants utilized by voles and grouse, I suggest that food quality is the ultimate factor for the synchrony in vole and grouse numbers in Norway.     

Habitat Effects on the Breeding Performance of Three Forest-Dwelling Hawks

Habitat loss causes population declines, but the mechanisms are rarely known. In the European Boreal Zone, loss of old forest due to intensive forestry is suspected to cause declines in forest-dwelling raptors by reducing their breeding performance. We studied the boreal breeding habitat and habitat-associated breeding performance of the northern goshawk (Accipiter gentilis), common buzzard (Buteo buteo) and European honey buzzard (Pernis apivorus). We combined long-term Finnish bird-of-prey data with multi-source national forest inventory data at various distances (100–4000 m) around the hawk nests. We found that breeding success of the goshawk was best explained by the habitat within a 2000-m radius around the nests; breeding was more successful with increasing proportions of old spruce forest and water, and decreasing proportions of young thinning forest. None of the habitat variables affected significantly the breeding success of the common buzzard or the honey buzzard, or the brood size of any of the species. The amount of old spruce forest decreased both around goshawk and common buzzard nests and throughout southern Finland in 1992–2010. In contrast, the area of young forest increased in southern Finland but not around hawk nests. We emphasize the importance of studying habitats at several spatial and temporal scales to determine the relevant species-specific scale and to detect environmental changes. Further effort is needed to reconcile the socioeconomic and ecological functions of forests and habitat requirements of old forest specialists.     

Coupling in goshawk and grouse population dynamics in Finland

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.     

Alloparental care in the sea: Brood parasitism and adoption within and between two species of coral reef Altrichthys damselfish?

The evolution of parental care opens the door for the evolution of brood parasitic strategies that allow individuals to gain the benefits of parental care without paying the costs. Here we provide the first documentation for alloparental care in coral reef fish and we discuss why these patterns may reflect conspecific and interspecific brood parasitism. Species‐specific barcodes revealed the existence of low levels (3.5% of all offspring) of mixed interspecific broods, mostly juvenile Amblyglyphidodon batunai and Pomacentrus smithi damselfish in Altrichthys broods. A separate analysis of conspecific parentage based on microsatellite markers revealed that mixed parentage broods are common in both species, and the genetic patterns are consistent with two different modes of conspecific brood parasitism, although further studies are required to determine the specific mechanisms responsible for these mixed parentage broods. While many broods had offspring from multiple parasites, in many cases a given brood contained only a single foreign offspring, perhaps a consequence of the movement of lone juveniles between nests. In other cases, broods contained large numbers of putative parasitic offspring from the same parents and we propose that these are more likely to be cases where parasitic adults laid a large number of eggs in the host nest than the result of movements of large numbers of offspring from a single brood after hatching. The evidence that these genetic patterns reflect adaptive brood parasitism, as well as possible costs and benefits of parasitism to hosts and parasites, are discussed.     

Spatial synchrony in red grouse population dynamics

Red grouse Lagopus lagopus scoticus populations exhibit unstable dynamics that are often characterised by regular periodic fluctuations in abundance. Time-series' of grouse harvesting records collected from 287 management units (moors) across Scotland, England and Wales were analysed to investigate the broad scale patterns of synchrony in these fluctuations. Estimation of the spatial autocorrelation of grouse population dynamics across moors indicates relatively high levels of synchrony between populations on adjacent moors, but that this synchrony declines sharply with increasing inter-moor distance. At distances of greater than 100  km, grouse population time-series exhibit only weakly positive cross-correlation coefficients. Twenty-eight geographical, environmental and other candidate variables were examined to construct a general linear model to explain variation in local synchrony. Grouse moor productivity (average size of shooting bag), distance from the Atlantic coast moving in a north-easterly direction, April and June temperatures, and June rainfall significantly increased the explanatory power of this model. An understanding of the processes underlying synchrony in red grouse population dynamics is a prerequisite to anticipating the effects of large-scale environmental change on regional patterns of grouse distribution and abundance.     

Avoidance of Filial Cannibalism in the Amphipod Gammarus pulex

Adult animals that cannibalise juvenile conspecifics may gain energy but also risk filial cannibalism, that is, consumption of their own offspring. However, individuals vary in the magnitude of the costs and benefits of cannibalism depending on factors such as their current energy reserves or the probability that they have offspring in the vicinity. They may therefore also vary in the extent to which they participate in cannibalism. This study investigated whether the sex or brooding status of adult amphipods (Gammarus pulex) influenced whether they participated in cannibalism of juveniles. For females carrying embryos within their brood pouch, we also investigated two hypotheses to explain the presence or absence of cannibalistic behaviour by determining whether cannibalism was correlated with factors that might reflect energy demands (body length, brood size), or that might reflect a temporal change in cannibalistic behaviour (corresponding to stage of brood development). All reproductive classes of adults participated in some level of juvenile cannibalism, but females carrying offspring at an advanced stage of development (close to emergence from the brood pouch) consumed significantly fewer juveniles than other groups. Females thus appear to significantly reduce cannibalism of juveniles concurrent with the time when their own eggs are hatching within the brood pouch, prior to the release of their offspring. Because the experiment tested female responses to unfamiliar juveniles, this reflects a temporal change in behaviour rather than a response to phenotypic recognition cues, although additional direct recognition cannot be ruled out. Brooding females with large brood sizes or large body lengths, which might have disproportionately greater energetic demands, were not more likely to cannibalise juveniles. We also noted that juveniles that survived in trials where cannibalism occurred were significantly more likely to be found at the water surface, suggesting a possible adaptation to escape cannibalistic adults. Overall, our results provide evidence that amphipods use indirect temporal cues to avoid filial cannibalism.     

Territory occupancy rate of goshawk and gyrfalcon: no evidence of delayed numerical response to grouse numbers

Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2–3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern Norway, however, subadult (two-year-old) goshawk hens occupied only 18–25% of territories where occupancy was not recorded in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather (most important for the gyrfalcon) should also be addressed. During 1988–2006, the annual proportion of goshawk territories with recorded nesting attempts in southern Norway was most closely related to the preceding autumn’s population indices of black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse cycles.     

Breeding success and chronology of Wood Storks Mycteria americana in northern and central Florida, U.S.A.

The breeding success and chronology of Wood Storks Mycteria americana were studied at eight colonies in northern and central Florida during 1981–1985. Mean ± s.d. clutch size for all colony-years was 3.07 ± 0.56 (n = 2694 nests), with three-egg clutches (72%) most frequent. Mean clutch size among all colonies and years ranged from 2.73 ± 0.55 to 3.41 ± 0.61. Many colonies exhibited significant negative trends in clutch size with, hatching date because of a proportional decrease in four-egg clutches later in the season. Mean colony clutch size was not correlated with nest numbers, nesting density or mean hatching date within most years. Mean ± s.d. number of fledglings for all colonies and years was 1.29 ± 1.16 fledglings per nest (n = 2812 nests). Mean annual fledging rates in colonies ranged from 0 (colony failed) to 2.66 fledglings per nest. Most breeding failure occurred prior to egg hatching, and the second highest mortality occurred between hatching and 2 weeks of age. Four-egg clutches fledged more storks than three-egg clutches, which in turn were more successful than two-egg clutches. However, all clutch sizes showed similar fledgling per egg rates. The seasonal decline in productivity was associated proportionally with smaller clutch sizes later in the breeding season. An increase in mean hatching date was correlated with an increase in latitude. There was greater within-year breeding synchrony among colonies than interyear breeding synchrony within each colony. Breeding synchrony was not correlated with mean hatching date, latitude, longitude, nest numbers or nesting density.     

A sex-specific size–number tradeoff in clonal broods

Polyembryonic parasitoids producing single-sex broods of clonal offspring provide an unusually clear window into the classic tradeoff between the number and size of offspring. We conducted a laboratory study of the encyrtid parasitoid Copidosoma bakeri parasitizing the noctuid Agrotis ipsilon to examine the way that size and number of offspring tradeoff in broods of each sex and to determine how the fit between host and parasitoid brood is achieved. We found that brood mass (wasp body mass ×brood size) was proportional to host mass, independent of brood sex, indicating a tight fit between brood and host and ensuring a size–number tradeoff. By correcting brood size and body mass of each brood for host mass, we demonstrated the expected inverse relationship between wasp variables. We postulated that the wasp brood might achieve the fit to the host by (1) adjusting brood size based on information available early in host development before and during division of the embryo, (2) manipulating host size late in host development after completion of embryo division, or (3) simply adjusting individual wasp mass to fill the host. We evaluated host responses to parasitism – and correlations between brood size and host growth early and late in development – for broods of each sex. The data are consistent with adjustment of brood size to the amount of host growth early in host development and with manipulation of host mass late in host development. The tight link between host mass and brood mass also suggests a final adjustment by parasitoid growth to achieve complete filling. Within the tight fit, female broods were smaller but contained larger individuals than male broods. The sex-specific balance point of the tradeoff and sex differences in balancing mechanisms and responses to host size suggest different selection pressures on each sex requiring future investigation.     

Diet of the golden eagle Aquila chrysaetos during the breeding season in Sweden

During a five-year period, 1975–1979, a total of 2881 prey individuals of 65 prey species were collected at 162 golden eagle nests from northern Sweden and from the island of Gotland. In northern Sweden birds are taken in higher numbers than mammals but calculated as weight the two categories are of equal importance, The main prey during the breeding season are capercaillie, black grouse, willow grouse, ptarmigan, mountain hare and reindeer fawns which together form 91% of the total food biomass. The capercaillie and the black grouse are taken more in the southern part of the coniferous region than in the northern. In contrast, in northern areas, reindeer fawns are more preyed upon than in the South, Ptarmigan and willow grouse are the most commonly captured prey species in mountain areas. The total number of reindeer fawns taken (dead and/or alive) by the Swedish golden eagle population during one summer is estimated at 600 individuals. On Gotland the golden eagles take mammals more often than in its northern distribution area. Rabbit and hedgehog arc the most important species.     

A novel PCR‐based genetic marker shows that sex of offspring does not account for hatch‐order effects on growth,survival and dominance in Pūkeko Porphyrio melanotus melanotus

Intra‐brood competition can influence a variety of fitness‐related traits in birds. Previous research on the joint‐nesting Pūkeko Porphyrio melanotus melanotus, a New Zealand subspecies of Australasian Swamphen, showed that chicks that hatched earlier in a brood tended to grow faster, were more likely to survive and had higher dominance status as adults than later hatched nest‐mates. However, this finding could be due to changes in offspring sex ratio across hatch order (e.g. if males tend to hatch earlier), which was not previously examined because of methodological challenges associated with sexing nestling Pūkeko. Here, we report a useful PCR‐based genetic marker to determine the sex of Pūkeko. We then used new sex‐specific data to re‐examine patterns of offspring growth, survival and dominance. We found that the sex of offspring does not account for the hatching‐order patterns related to social dominance, growth or survival. Furthermore, changes in offspring sex ratio across hatching‐order were negligible and offspring sex ratios did not differ significantly between the primary female and secondary female broods (in joint‐clutch nests), or when comparing primary female and single female broods. We found no clear evidence for sex ratio bias according to hatching‐order and conclude that hatching‐order and not offspring sex explain patterns of growth, survivorship and adult dominance in Pūkeko.     

Sex ratio and maternal investment in the multivoltine large carpenter bee Xylocopa sulcatipes (Apoideh: Anthophoridae)

Abstract. 1. Females of the multivoltine carpenter bee Xylocopa sulcutipes (Maa) (Hymenoptera: Anthophoridae) usually excavate a straight tunnel in dead twigs and mass provision a linear array of up to ten brood cells with pollen and nectar. An egg is deposited upon each food mass within one cell.
2. Female offspring generally receive a higher provisioning mass (0.180 ± 0.048 g) than males, a significant difference ( P > 0.001). There are, however, male larvae that receive as much food or more as their sisters or female larvae reared in another nest.
3. There is a close positive association between the size of a mother and the weight of provisions for individual daughters, but not for sons.
4. Female offspring are positioned in the innermost brood cells (Gositions 1, 2 and 3). The sex ratio of the outer cells is either significantly male biased (positions 4–6) or skewed towards males (positions 8 and 9). Positions 7 and 10 are in equilibrium.
5. Solitary females produce a significantly female biased sex ratio ( P < 0.01). Sex ratio in social nests is skewed toward females, but not significantly so ( P < 0.2). There is no significant difference between the sex ratio of solitary and social nests ( P = 0.361). The population sex ratio (pooled sex ratio of all broods produced) is significantly female biased ( P = 0.003).
6. Females kept in the laboratory produced female biased sex ratios whilst unmated females produced all-male broods indicating that insemination and ovarian development are not causally related.
7. The expected sex ratio (ESR) under equal investment, calculated as 1/CR (CR = mean male provision weight/mean female provision weight), is 137.5:117.5 (males:females), and differs significantly from that observed, 104:151 (males:females) ( P < 0.001). The 'Local Resource Enhlancement' hypothesis best explains the female biased sex ratio found in X.sulcatipes and its maintenance in the population.     

Shared reproduction and sex ratio adjustment to clutch size in a socially polymorphic orchid bee

Nests of the primitively eusocial orchid bee Euglossa viridissima are generally founded by a solitary female but can be reactivated by female offspring, in the presence or absence of the mother. The population therefore exists of solitary and social nests that co-occur in an area. A female can stay as a subordinate helper under a dominant female or disperse to become a solitary foundress. Yet, the costs and benefits of the different social phenotypes are so far little understood. Here, we compared solitary and social nests of orchid bees. We used offspring of solitary and social nests to calculate offspring sex ratio, and applied molecular markers to calculate intranidal relatedness, infer maternity and test whether sociality may have a genetic component. We found that social nests had on average more brood than solitary nests. The overall sex ratio in the population did not differ from 1:1. However, social nests tended to produce a split sex ratio with some nests producing mainly males and others mainly female offspring. Regardless of social phenotype, the number of offspring was correlated with the sex ratio, with smaller nests having a more female-biased offspring. In social nests, not all offspring resulted from a single-mated mother, which was also the case for some solitary nests. This suggests shared reproduction in social nests and may be an indication that intraspecific parasitism and nest takeover are not uncommon. Structure analyses did not reveal different genetic background of the two social phenotypes. Our results suggest that there is no clear benefit that favours one of the two social phenotypes over the other and that the population is kept at balance in terms of sex ratio.     

Successful adult willow grouse are exposed to increased harvest risk

Age and sex ratios in bag records are frequently used as indices of population composition for harvested populations. However, vulnerability to harvest may differ by age and sex thereby producing bias in population estimates. We assessed whether age and sex affected vulnerability to harvest for willow grouse (Lagopus lagopus) where adult density and brood size were known in the harvested populations. We collected bag records during 2 days of controlled hunting in 4 areas in 2 years (2007 and 2008) in Jämtland county, Sweden. We found that vulnerability to harvest was different for chicks and adults, but not between male and female adults. Hunters encountered broods at a higher rate than single birds compared to personnel conducting pre-harvest counts along line transects. Furthermore, the probability of shooting a grouse was higher in encounters of broods than individual grouse. Proportionally, we calculated about a 50% probability of a hunter shooting either a chick or an adult independent of encountering a single bird or broods of 2–10 grouse. Increasing adult density also increased the vulnerability to harvest for adults relative to chicks, independent of the chick to adult ratio in the pre-harvest population. The different vulnerability of adults and chicks to harvest observed in this study will dampen variation in age classes in bag records compared to the population, and we caution against extrapolation of age ratios in bag records to harvested populations. © 2012 The Wildlife Society.     

Impact of climate change and prey abundance on nesting success of a top predator, the goshawk

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.