Correlates of Common Buzzard Buteo buteo density and breeding success in the West Midlands

Buzzard density and breeding success in relation to habitat and Rabbit Oryctolagus cuniculus abundance was studied in the West Midlands from 1994 to 1996. We found densities of 81 and 22 territorial pairs per 100 km² in two areas 40 km apart; the former is the highest density yet recorded in Europe. High Buzzard breeding densities were associated with high proportions of unimproved pasture and mature woodland within estimated territories. Buzzards laid earlier clutches at lower altitudes and with high proportions of unimproved pasture close to nests. Large clutches and high numbers of fledged young were associated with high Rabbit abundance close to nests. Most nest failures occurred during incubation and were probably mainly due to corvid predation. Brood reduction was associated with low proportions of deciduous woodland close to nests and small clutch sizes, although the causes of chick mortality were uncertain. Rabbits were the main prey item found at nests with passerines, especially young corvids, also appearing frequently.     

Assessing prey provisioned to Common Buzzard Buteo buteo chicks: a comparison of methods

Capsule: Methods of assessing raptor diet carry significant inherent biases which can vary over time.

Aims: To compare methods of assessing Common Buzzard Buteo buteo diet composition and assess how any differences vary between years.

Methods: Diet was assessed at 32 Common Buzzard nests on an area of upland heather moorland in Britain, managed for Red Grouse Lagopus lagopus scotica, over three years. Data obtained from nest cameras were compared with data from prey remains and regurgitated pellets.

Results: Diet composition differed between methods in all years. Methodological differences varied between years in relation to an almost twelve-fold change in Field Vole abundance, a key prey of Common Buzzards, while abundances of alternative prey changed little. Small mammals were underestimated by prey remains in all three years, while herpetofauna were underestimated by prey remains and pellets in two years. Large birds were overestimated by prey remains, significantly so in one year. Pellets overestimated invertebrates in all years. By combining prey remains and pellets, significant yearly variations in biases were eliminated, although the combined measure overestimated large birds and invertebrates.

Conclusion: Our results suggest that future studies should consider not only how chosen methods may affect results, but also how effects can differ between years.     

Numerical and functional responses of Common Buzzards Buteo buteo to prey abundance on a Scottish grouse moor

Predators will often respond to reductions in preferred prey by switching to alternative prey resources. However, this may not apply to all alternative prey groups in patchy landscapes. We investigated the demographic and aggregative numerical and functional responses of Common Buzzards Buteo buteo in relation to variations in prey abundance on a moor managed for Red Grouse Lagopus lagopus scotica in south‐west Scotland over three consecutive breeding and non‐breeding seasons. We predicted that predation of Red Grouse by Buzzards would increase when abundance of their preferred Field Vole Microtus agrestis prey declined. As vole abundance fluctuated, Buzzards responded functionally by eating voles in relation to their abundance, but they did not respond demographically in terms of either breeding success or density. During a vole crash year, Buzzards selected a wider range of prey typical of enclosed farmland habitats found on the moorland edge but fewer Grouse from the heather moorland. During a vole peak year, prey remains suggested a linear relationship between Grouse density and the number of Grouse eaten (a Type 1 functional response), which was not evident in either intermediate or vole crash years. Buzzard foraging intensity varied between years as vole abundance fluctuated, and foraging intensity declined with increasing heather cover. Our findings did not support the prediction that predation of Red Grouse would increase when vole abundance was low. Instead, they suggest that Buzzards predated Grouse incidentally while hunting for voles, which may increase when vole abundances are high through promoting foraging in heather moorland habitats where Grouse are more numerous. Our results suggest that declines in their main prey may not result in increased predation of all alternative prey groups when predators inhabit patchy landscapes. We suggest that when investigating predator diet and impacts on prey, knowledge of all resources and habitats that are available to predators is important.     

The relationship of spring and summer weather with density and breeding performance of the Buzzard Buteo buteo, Goshawk Accipiter gentilis and Kestrel Falco tinnunculus

The density of territorial pairs, laying pairs and the breeding performance of three raptor species, Buzzard Buteo buteo , Goshawk Accipiter gentilis and Kestrel Falco tinnunculus , were investigated in relation to rainfall and temperature during the breeding cycle. In all species the density of territorial pairs was not related to spring rainfall and temperature. In the Buzzard the percentage of pairs that bred unsuccessfully was significantly related to May rainfall. The number of young fledged was negatively correlated with rainfall in April and May. In the Goshawk the percentage of laying pairs was negatively correlated to rainfall in March and April. Success in terms of number of young fledged was related mostly to May temperature. In the Kestrel the density of territorial pairs was dependent on March-April rainfall. The number of young fledged per successful pair was highly correlated with May and June temperature. All these relationships showed that the hatching period and the subsequent two weeks were most important for chick survival.     

Nesting habitat overlap between the Common Buzzard Buteo buteo and the Lesser Spotted Eagle Clanga pomarina for conservation planning in Natura 2000 sites

Capsule: The nesting habitat of the Common Buzzard Buteo buteo and Lesser Spotted Eagle Clanga pomarina extensively overlap, indicating that they exploit similar resources.

Aim: We aimed to determine the overlap in the nest platforms, nest trees and nest stands used by these raptors, find any evidence for the avoidance of the larger Lesser Spotted Eagle by the smaller Common Buzzard, and provide conservation implications for habitat protection of the former species in habitats that overlap extensively.

Methods: Nest sites were mapped during 2012–2014 in the Bir?ai Forest Spatial Protection Area, northern Lithuania. Fifty-three nest sites occupied by Common Buzzards and 26 by Lesser Spotted Eagles were compared.

Results: The nest platforms of both raptors were similarly placed in the tree canopies. Most Lesser Spotted Eagle nests were built in spruce, while the Common Buzzard usually nested in birch. The nest stands of the eagles were on wetter soil and located closer to the forest edge than those of the buzzards, otherwise, the nest stands did not differ significantly. There was no evidence for spatial avoidance of the larger raptor by the Common Buzzard.

Conclusions: The different components of the nesting habitats extensively overlapped, and the distribution of the interspecific pairs lacked spatial avoidance. We suggest that the nest sites of both raptors were a largely shared resource, especially if located close to the forest edges. We propose, as a rule of thumb, applying protection by way of buffer zones around buzzard nest sites if they are located close to eagle nest sites and the forest edge.     

The importance of competition,food, habitat,weather and phenotype for the reproduction of Buzzard Buteo buteo

Capsule Variation in reproduction between territories was strongly influenced by intra- and interspecific competition, phenotype, levels of rainfall and human disturbance.

Aims To assess the relative importance of competition, food, habitat quality, weather and phenotype as predictors of variation in reproduction in Buzzard.

Methods Annual breeding data were collected from 1989 to 1996 in a 300-km² study area and related to 35 independent variables through multivariate regression models.

Results Significant predictors of variation in reproduction between territories (78% variance explained) were variables describing intra- and interspecific competition, plumage morph, laying date, precipitation levels and anthropogenic disturbances in the breeding territory. Competition and plumage morph seem to be particularly important, as these variables explained a high level of variation (81%) in the 1996 reproduction of this population.

Conclusion The potential importance of competition, plumage morph and precipitation for reproduction in this Buzzard population is emphasized.     

Winter diet of Common Buzzards Buteo buteo on a Scottish grouse moor

Capsule: The winter diet of Common Buzzards Buteo buteo on a Red Grouse Lagopus lagopus scotica moor was dominated by small mammals, whilst grouse were a minor prey item.

Aims: To assess winter diet of Common Buzzards from pellets collected at roost sites on and around a managed Red Grouse moor, and to explore temporal, spatial and age-related variation in diet composition.

Methods: Forty-four winter roost sites were located during two winters using a combination of observations from vantage points and individual Common Buzzards equipped with either radio or satellite transmitters. Pellets were collected between October and March each winter and analysed to assess dietary composition.

Results: Small mammals were the main prey in both years, comprising 60–67% of items and occurring in 88–92% of pellets. Diet varied between years, with more lagomorphs and birds (passerines, corvids and pigeons) but fewer Red Grouse eaten when grouse abundance declined. Grouse formed 1.1% and 0.6% of prey items, and occurred in 3% and 2% of pellets from each winter, respectively.

Conclusion: Common Buzzards rely on small mammal prey during winter. When available, Red Grouse are a minor dietary component, the amount of which reflects their abundance in the environment. The opportunism of Common Buzzards can result in temporal variation in winter diet.     

Behaviour in the post-nestling dependence period of radio-tagged Common Buzzards Buteo buteo

Behaviour of 26 young Common Buzzards Buteo buteo was studied by systematic radiotracking during July and August 1991. After hatching between 11 May and 18 June, the young buzzards fledged when they were 43–54 days old. Distances travelled from the nest increased abruptly after birds were 65 days old, when their flight feathers had completed growth: buzzards were located more than 500 m from the nest in only 2% of records within 65 days of hatching but in 26% of records when they were older. Before their 65th day, there was an increase with age in distance from the nest, time spent flying and time spent calling, especially for buzzards with continuous woodland around the nest. The increases in distance and areas covered were greatest for broods where parents were most often present, which was at nests with the most grass and arable farmland nearby. Between their 65th and 100th days, buzzards showed no increase in activity with age and called less, especially where there was extensive woodland, and travelled farthest from nests with least neighbouring grassland; broods with few young most often had parents nearby. Young buzzards associated strongly with each other between leaving the nest and completing feather growth, but some broods later became much less cohesive. Variation in activity was not linked to sex or to the presence of 30 g back-pack radio-tags compared with 12-g leg-mounted radio-tags.     

Buzzards Buteo buteo and Ravens Corvus corax in the uplands of Britain: limits to distribution and abundance

The current breeding ranges of Buzzards Buteo buteo and Ravens Corvus corax in Britain are restricted to the west, and both are relics of former widespread but not necessarily even distributions. Moore (1957) attributed the Buzzard's contraction in range to persecution by gamekeepers, his evidence being the complementary nature of the Buzzard's distribution with those of gamekeepers in the lowlands and grouse moors in the uplands; others have attributed the Raven's decline to the same cause. Is Moore correct and, if so, are these species' ranges still limited by persecution? Here we adopt an approach similar to Moore's, whereby we compare the current geographical patterns of abundance of Buzzards and Ravens in the British uplands with that of an index of grouse moor density. Unlike Moore, however, we take into account climate, land cover, topography and sheep stocking density, as well as grouse moor distribution, using multiple logistic regression modelling. We show that in the uplands the distribution of grouse moors strongly limits that of Buzzards and Ravens but are unable to conclude that this is a result of persecution because there are several competing hypotheses (moor management, food and nest-site availability) between which we are unable to distinguish.     

Population change of Common Buzzards Buteo buteo in central southern England between 2011 and 2016

ABSTRACT

Capsule: Distance sampling identified an increase in estimated population size of Common Buzzards Buteo buteo in central southern England between 2011 and 2016 of more than 50%. The rate of population growth slowed in later years.

Aims: To assess the utility of a targeted distance sampling protocol to derive seasonal and annual population estimates for Common Buzzards across an area of southern England.

Methods: We used a line transect survey methodology and multiple covariate distance sampling to assess population density and abundance of Common Buzzards in spring and autumn between 2011 and 2016 across a 2600?km² area of central southern England.

Results: Estimated population size increased by more than 50%, from approximately 2900 to 4500 individuals, across the period in a trend similar to that shown by Breeding Bird Survey data.

Discussion: A slowing of the growth in population size of Common Buzzards in central southern England suggests that the species may be approaching carrying capacity in this area. These results also suggest that currently employed broad scale survey methodologies adequately reflect the general population trends for this species. Our data provide the first published estimates of the Common Buzzard population in central southern England derived from direct empirical assessment.     

Climate change and habitat heterogeneity drive a population increase in Common Buzzards Buteo buteo through effects on survival

The effect of changing climatic conditions on wild populations has been the subject of much recent research. Most attention has been on the direct effects of climate changes on species of lower trophic levels and on the negative consequences of climate change. However, a deeper understanding of how climate change affects apex predators is vital, as they are keystone species that have a disproportionate effect on ecosystems. Studying survival in an apex predator requires individual‐based data from long‐term studies and is complicated by the integration of climatic effects on lower trophic levels. Here we assess how climate affects the survival of the Common Buzzard Buteo buteo. We analysed the survival of 670 males and 669 females over the period 1989–2011, during which time our study population quadrupled. We used mark–recapture survival analysis of individual resightings of breeding adults to identify the environmental factors best explaining survival. A decrease in the North Atlantic Oscillation (NAO) index increased survival to an extent that largely explains the population increase. This might be caused by higher Common Vole Microtus arvalis survival in drier conditions and under snow cover. Buzzard survival appeared to increase more for males than for females, possibly due to the males' higher sensitivity to winter food availability resulting from their smaller body mass. However, we also found that the effect of NAO strongly depended on the area in which individuals lived, especially for females. This may have been caused by the recolonization of Eagle Owls Bubo bubo in some parts of our study area. This study suggests that climatic changes can have complex effects on species of higher trophic levels via an interaction with their prey.     

Correlates of the population increase of Common Buzzards Buteo buteo in the West Midlands between 1983 and 1996

Buzzard density and distribution increased significantly in the West Midlands between 1983 and 1996. The number of soaring Buzzards counted in spring increased by 118% in the main range, 348% in the edge range and 231% overall. Although there was no significant linear trend in breeding success between 1950 and 1995, numbers of young fledged per breeding attempt were highest in the period 1980–95. This high productivity coincided with an increase in Rabbit Oryctolagus cuniculus abundance. Persecution levels, especially poisonings, appear to have been lower in the 1990s than during 1975–89. Increased productivity due to high Rabbit abundance, and higher survival rates due to reduced persecution, are likely to be the main factors responsible for the rapid increase in the Buzzard population in this area. Buzzards are increasing in numbers in other parts of Britain and Ireland and may now be more numerous than at any time this century.     

The influence of prey fluctuations on the breeding success of the Tawny Owl Strix aluco

A population of 17 to 20 pairs of Tawny Owls was studied from 1959–79 in Grunewald forest, West Berlin. The breeding success of the Owls (21–77% of pairs raising young per year) and the proportion of yellow-necked field mice Apodenzus flavicollis in their pellets (13–48% of prey items each year) exhibited the same three-year cycle. Long-term trends in the diet of the Owls were apparent and reasons for these are discussed.     

Age-related differences in abundance and habitat occupation of Steppe Buzzards,Buteo buteo vulpinus,in the Western Cape Province,South Africa

Linear densities of Steppe Buzzards, Buteo buteo, were studied along roads at the southernmost edge of the nonbreeding range in the Western Cape Province, South Africa. Adults arrived before first-year birds; peak populations of the former occurred from December to February, and of the latter from January onwards. Except during periods with rapidly changing numbers during arrival and departure, the proportion of first-year birds in three different areas was negatively related to the density of adults. This may be the result of competitive exclusion by adults, or of age-related differences in habitat preference. Adults dominated first-year birds at hunting perches. First-year birds were most frequently found in more closed habitat, where they attempted to kleptoparasitize adults in 18% of all observed instances of prey mantling.     

The effect of pollination on the growth and reproduction of oilseed rape (Brassica napus)

Phenotypic plasticity is an organism's ability to alter its development and life history in response to environmental conditions. In plants, biotic and abiotic factors drive the distribution of resources between growth and reproductive traits. One such biotic factor is pollination. Studies show that wind and insect pollination enhance oilseed rape (Brassica napus) yield. However, the impact of pollination on resource allocation towards growth and reproduction is less understood. We conducted a controlled experiment to assess the effect of pollination on growth and functional reproductive traits. We compared two simulated supplementary pollen deposition methods (representing wind and insect pollination) alongside a non-supplementary control. Pollinated plants allocated resources towards growth and reproduction similarly, irrespective of deposition method. Plants receiving no supplementary pollination produced fewer seeds, allocating resources to growth, more prolific and persistent flowering, and heavier seeds. Pollinated plants had a reduced flowering period and were shorter, indicating resources were allocated to seed production rather than growth or the production of additional flowers. This allocation of resources from growth and flowering metrics can increase yield directly through increased seed production and indirectly through shorter plants and a reduced flowering period with seeds that mature earlier (agronomically beneficial traits).Wind and insect pollination can enhance and stabilise oilseed rape yield under various environmental conditions by acting in complementary ways. Since pollination limits yield in oilseed rape, it must be considered an input that can be actively managed. Successful management of pollination services requires growers to detect pollination deficits. Inadequately pollinated oilseed rape plants exhibit apparent morphological changes (e.g. taller plants that flower for longer), acting as an early warning to growers. Equipping growers with this knowledge provides them with a means of detecting deficits and thus enables them to take positive action to restore pollination services by introducing honeybees or enhancing wild pollinators.     

The breeding success of Common Swifts Apus apus is not correlated with the abundance of their Louse Fly Crataerina pallida parasites

Capsule Parasitism has no apparent detrimental effect.

Aims To determine whether parasitism by a haematophagous nest ectoparasite, the Louse Fly Crataerina pallida has a detrimental effect on the reproductive success of its Common Swift Apus apus hosts.

Methods An association between C. pallida abundance and various host life‐history parameters indicative of host reproductive success were sought.

Results No relationship was found between measures of parasite load and clutch size, brood size, length of time required to reach nestling asymptotic weight, the length of time from hatching to fledging, fledging success per nest, fledgling weight, and fledgling size.

Conclusion Parasitism has no apparent detrimental effect upon its hosts. Louse Flies may have evolved low levels of virulence or the negative effects expected as a consequence of its parasitism may be expressed on life‐history traits other than those studied here.     

The effect of prey composition and abundance on the predation rate and selectivity ofMysis relicta

The predation rate and selection of specific prey byMysis relicta in Lake Tahoe depends on both the total and the relative densities of prey classes. Functional responses of mysids to changes in the density of two species of calanoid copepod prey were curvilinear in laboratory experiments. In the field and in 2-prey treatments, preference was usually positive forEpischura and negative forDiaptomus. However, the preference forEpischura was greatest at the lowest combined densities of prey in the laboratory and decreased at densities >100Epischura / m3 in the field. Several hypotheses to explain the inverse relationship between selectivity and prey density are discussed. Field assemblages of prey vary vertically, horizontally and seasonally. Potential effects of this hetrogeneity on both predator and prey populations are examined.     

Hepatic biotransformation in the buzzard (Buteo buteo) and the Japanese quail (Coturnix coturnix): effect of PCBs

Hepatic biotransformation was studied in microsomal (cytochrome P-450-dependent monooxygenase activities) and cytosolic (glutathione S-transferase activities) fractions from Japanese quail (Coturnix coturnix) and buzzard (Buteo buteo). Monooxygenase activities were not very different apart from a high 7-ethoxycoumarin de-ethylase activity in quail as compared to buzzard. Glutathione S-transferase activities were higher in quail than in buzzard. DP5 (a commercial mixture of PCBs containing 50% chlorine) produced a marked increase in monooxygenase activity from quail liver. In contrast, no induction was found in buzzard under the same conditions. Glutathione S-transferase activities were not modified in both species.