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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.

Six adult and three juvenile honey buzzards Pernis apivorus were radio-tracked by satellite during autumn migration from southwestern Sweden. All adults crossed the Mediterranean Sea at the Strait of Gibraltar and continued across the Sahara desert to winter in West Africa, from Sierra Leone to Cameroon. Analysing three main steps of the migration, (1) from the breeding site to the southern Mediterranean region, (2) across the Sahara and (3) from the southern Sahara to the wintering sites, the adults changed direction significantly between these steps, and migrated along a distinct large-scale detour. In contrast, the juveniles travelled in more southerly directions, crossed the Mediterranean Sea at various places, but still ended up in the same wintering areas as the adults. Average speeds maintained on travelling days were similar for the two age groups, about 170 km/day in Europe, 270 km/day across Sahara and 125 km/day in Africa south of Sahara. However, as the adults used fewer stopover days en route, they maintained higher mean overall speeds and completed migration in a shorter time (42 days) than the juveniles (64 days). Although the juveniles set out on more direct courses towards the wintering grounds, they did not cover significantly shorter distances than the adults, as they tended to show a larger directional scatter between shorter flight segments. The results corroborate previous suggestions that adult and juvenile honey buzzards follow different routes during autumn migration, and that the birds change migration strategy during their lifetime. While juveniles may use individual vector orientation, social influences and learning may be of great importance for the detour migration of adults. The remarkable and distinct age-dependent shift in migratory route and orientation of the honey buzzard provides a challenging evolutionary problem.

In this paper we aim to explain the distribution of red-breasted geese Branta ruficollis over different nesting habitats. To be safe from land predators red-breasted goose colonies were restricted to i) islands on rivers, ii) cliffs with peregrine falcons Falco peregrinus, and iii) the close proximity of snowy owl Nyctea scandiaca and rough-legged buzzard Buteo lagopus nests. Among years nest site availability varied by fluctuations in numbers of owls and buzzards in association with cycles in lemming abundance, but the total number of goose nests found in the study area did not vary. The distribution of geese, in combination with data on reproductive success, suggested a despotic mechanism: at cliffs, goose numbers were constant among years with an invariably high reproductive success, whereas large fluctuations in numbers on islands coincided with opposite trends in success. Apparently, geese nesting with owls or buzzards moved to the few islands present in the study area during years when these birds of prey were absent. Consequently, in such years the average density of geese on islands was more than twice as high as at cliff colonies (5.4 and 2.3 pairs per ha of foraging habitat, respectively). Colony size at cliffs may have been restricted by territorial behaviour of the geese, though there is evidence that, additionally, the host falcons also limited the number of nesting geese. Apparently rare in closely related species, we observed a negative density-dependent effect on reproductive success during the nest phase, and attribute this to limited food resources, reinforced by the high frequency of territorial interactions. This leads to the conclusion that, in addition to predation pressure, nesting density is an important agent in the link between lemming cycles and goose breeding success.

Age-specific survival and breeding (ASSAB) models were developed with data from 146 common buzzards (Buteo buteo) radio-tagged in southern Britain during 1990-1998, in a 120-km(2) study area that had on average 25 egg-laying pairs. Survival checks were aided by philopatric behaviour and a maximum annual tag failure rate of 7%: minimum survival rates, that were estimated by assuming death of buzzards with lost tags, were close to maximum rates that were estimated using only the recorded deaths. First-year survival rate estimates for 35 buzzards fitted in 1990-1991 with 25-30-g backpack radios were 69-74% (minimum-maximum), close to the 61-71% for 16 buzzards with 12-g tail-mount radios; the backpacks transmitted for 2-4 yr. Overall survival rates were 66-73% in the first year, 91-97% in the second and 88-91% thereafter. Survival estimates from 258 recent British ring recoveries were lower in the first and second years, at 55% and 75%, but similar (88%) thereafter. Most deaths were from natural causes (40%) or interaction with artefacts (36%). ASSAB models. from radio-tracking and the observed 1.71 young clutch(-1), predicted breeding by 16-21% of all the buzzards present in spring, or up to 25% with the minimum likely productivity of 1.4 young clutch(-1) or 12% net emigration. Ringing data predicted breeding rates of 33-38%. The models were tested with density data from nest surveys and new radio-corrected-transect and truncation-mark-resighting estimates of buzzard numbers. Surveys in autumn and late winter estimated breeding rates of 21-25%. The high non-breeder density in spring. of three other buzzards for each paired bird with eggs, has important implications for understanding evolutionary fitness, predation and population ecology.

The annual variability of the breeding performance of rodentivorous birds of prey has traditionally been explained in terms of annual fluctuations in rodent abundance. This paper presents data from the Siberian tundra showing that this relationship may not be so simple as generally thought. The data consist of parameters of small mammal population fluctuations (small mammal density (SMD), average body weight, species diversity and rate of change of species diversity), inter-specific competition and meteorological factors (mean temperature and snow melt date) during every stage of the breeding cycle of the rough-legged buzzard (Buteo lagopus). The density of breeding pairs was found to be correlated with the SMD, whereas the total number of territorial pairs including non-breeding ones could be most accurately predicted by a model incorporating both the SMD and the population density of a larger competitor, the snowy owl (Nyctea scandiaca). Clutch size showed no correlation with the SMD. The best-fit multiple regression model to predict clutch size includes only small mammal diversity and its rate of change as predictive factors. Number of nestlings and egg losses did not show any correlation with any of the prey-related or weather parameters. Although the total number of rough-legged buzzard fledglings produced per unit area showed a significant positive correlation with the SMD in a single-factor regression, the most accurate multiple regression model to predict overall reproductive output included only the rate of change of the small mammal species diversity. The number of offspring produced by the buzzards in a given area fluctuated synchronously with the SMD, but the cycle was significantly more consistent in amplitude in the predator as compared to the prey.