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R E Kenward - One of the best experts on this subject based on the ideXlab platform.

  • movements of radio tagged buzzards Buteo Buteo in early life
    Ibis, 2008
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    Radio-tags were used to track 146 Buzzards Buteo Buteo during 1990-1996. Each bird was tracked for up to 4 years; of 74 tags fitted since 1992, 72% lasted 3 years. Among the 87 Buzzards tracked for more than one year, 46% settled after one dispersal movement, 37% dispersed and then changed their ranges, 17% did not disperse and one Buzzard alternated between a summer and a winter range. Natal dispersal occurred in two waves, one in the first autumn and the second in the following spring. Initial dispersal distances in the autumn were significantly greater than those in the spring. For 73 Buzzards that dispersed in their first autumn, 96% settled within 100 km of their nest, and their distances were similar to 76 ringing recoveries. After their second spring, Buzzards rarely changed ranges and were significantly more often to the east than the west, especially those that had dispersed more than 20 km. Buzzards that had dispersed furthest were most likely to be detected returning towards their natal area in spring, and returned earlier as they got older. However, none were detected returning once they had started to breed. Nine early breeders were significantly farther from their natal nests than 44 non-breeders.

  • Movements of radio‐tagged Buzzards Buteo Buteo in early life
    Ibis, 2008
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    Radio-tags were used to track 146 Buzzards Buteo Buteo during 1990-1996. Each bird was tracked for up to 4 years; of 74 tags fitted since 1992, 72% lasted 3 years. Among the 87 Buzzards tracked for more than one year, 46% settled after one dispersal movement, 37% dispersed and then changed their ranges, 17% did not disperse and one Buzzard alternated between a summer and a winter range. Natal dispersal occurred in two waves, one in the first autumn and the second in the following spring. Initial dispersal distances in the autumn were significantly greater than those in the spring. For 73 Buzzards that dispersed in their first autumn, 96% settled within 100 km of their nest, and their distances were similar to 76 ringing recoveries. After their second spring, Buzzards rarely changed ranges and were significantly more often to the east than the west, especially those that had dispersed more than 20 km. Buzzards that had dispersed furthest were most likely to be detected returning towards their natal area in spring, and returned earlier as they got older. However, none were detected returning once they had started to breed. Nine early breeders were significantly farther from their natal nests than 44 non-breeders.

  • behaviour in the post nestling dependence period of radio tagged common buzzards Buteo Buteo
    Ibis, 2008
    Co-Authors: A J Tyack, S S Walls, R E Kenward
    Abstract:

    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.

  • Movements of radio‐tagged Common Buzzards Buteo Buteo in their first year
    Ibis, 1995
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    The movements of 96 radio-tagged juvenile Common Buzzards Buteo Buteo were studied during 3 years in Dorset, southern England. Contrary to previous studies which implied that Common Buzzards are territorial, we found that 39% foraged within 1 km of the nest during their first winter, presumably within their parents' home range. Most (72%) of those that did not disperse were recorded making brief excursions during August and September, before opting for a “stay-at-home” strategy. There was no significant difference between the sexes in the tendency to make excursions or disperse, but females dispersed further than males. Buzzards which dispersed early tended to settle significantly farther from their nests than did late dispersers. Long-term radio-tracking has shown that 72% of the dispersing birds returned towards their natal area in the following breeding season. Such philopatry may be an important hindrance to avian recolonization following local extinctions.

  • movements of radio tagged common buzzards Buteo Buteo in their first year
    Ibis, 1995
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    The movements of 96 radio-tagged juvenile Common Buzzards Buteo Buteo were studied during 3 years in Dorset, southern England. Contrary to previous studies which implied that Common Buzzards are territorial, we found that 39% foraged within 1 km of the nest during their first winter, presumably within their parents' home range. Most (72%) of those that did not disperse were recorded making brief excursions during August and September, before opting for a “stay-at-home” strategy. There was no significant difference between the sexes in the tendency to make excursions or disperse, but females dispersed further than males. Buzzards which dispersed early tended to settle significantly farther from their nests than did late dispersers. Long-term radio-tracking has shown that 72% of the dispersing birds returned towards their natal area in the following breeding season. Such philopatry may be an important hindrance to avian recolonization following local extinctions.

S S Walls - One of the best experts on this subject based on the ideXlab platform.

  • movements of radio tagged buzzards Buteo Buteo in early life
    Ibis, 2008
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    Radio-tags were used to track 146 Buzzards Buteo Buteo during 1990-1996. Each bird was tracked for up to 4 years; of 74 tags fitted since 1992, 72% lasted 3 years. Among the 87 Buzzards tracked for more than one year, 46% settled after one dispersal movement, 37% dispersed and then changed their ranges, 17% did not disperse and one Buzzard alternated between a summer and a winter range. Natal dispersal occurred in two waves, one in the first autumn and the second in the following spring. Initial dispersal distances in the autumn were significantly greater than those in the spring. For 73 Buzzards that dispersed in their first autumn, 96% settled within 100 km of their nest, and their distances were similar to 76 ringing recoveries. After their second spring, Buzzards rarely changed ranges and were significantly more often to the east than the west, especially those that had dispersed more than 20 km. Buzzards that had dispersed furthest were most likely to be detected returning towards their natal area in spring, and returned earlier as they got older. However, none were detected returning once they had started to breed. Nine early breeders were significantly farther from their natal nests than 44 non-breeders.

  • Movements of radio‐tagged Buzzards Buteo Buteo in early life
    Ibis, 2008
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    Radio-tags were used to track 146 Buzzards Buteo Buteo during 1990-1996. Each bird was tracked for up to 4 years; of 74 tags fitted since 1992, 72% lasted 3 years. Among the 87 Buzzards tracked for more than one year, 46% settled after one dispersal movement, 37% dispersed and then changed their ranges, 17% did not disperse and one Buzzard alternated between a summer and a winter range. Natal dispersal occurred in two waves, one in the first autumn and the second in the following spring. Initial dispersal distances in the autumn were significantly greater than those in the spring. For 73 Buzzards that dispersed in their first autumn, 96% settled within 100 km of their nest, and their distances were similar to 76 ringing recoveries. After their second spring, Buzzards rarely changed ranges and were significantly more often to the east than the west, especially those that had dispersed more than 20 km. Buzzards that had dispersed furthest were most likely to be detected returning towards their natal area in spring, and returned earlier as they got older. However, none were detected returning once they had started to breed. Nine early breeders were significantly farther from their natal nests than 44 non-breeders.

  • behaviour in the post nestling dependence period of radio tagged common buzzards Buteo Buteo
    Ibis, 2008
    Co-Authors: A J Tyack, S S Walls, R E Kenward
    Abstract:

    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.

  • Movements of radio‐tagged Common Buzzards Buteo Buteo in their first year
    Ibis, 1995
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    The movements of 96 radio-tagged juvenile Common Buzzards Buteo Buteo were studied during 3 years in Dorset, southern England. Contrary to previous studies which implied that Common Buzzards are territorial, we found that 39% foraged within 1 km of the nest during their first winter, presumably within their parents' home range. Most (72%) of those that did not disperse were recorded making brief excursions during August and September, before opting for a “stay-at-home” strategy. There was no significant difference between the sexes in the tendency to make excursions or disperse, but females dispersed further than males. Buzzards which dispersed early tended to settle significantly farther from their nests than did late dispersers. Long-term radio-tracking has shown that 72% of the dispersing birds returned towards their natal area in the following breeding season. Such philopatry may be an important hindrance to avian recolonization following local extinctions.

  • movements of radio tagged common buzzards Buteo Buteo in their first year
    Ibis, 1995
    Co-Authors: S S Walls, R E Kenward
    Abstract:

    The movements of 96 radio-tagged juvenile Common Buzzards Buteo Buteo were studied during 3 years in Dorset, southern England. Contrary to previous studies which implied that Common Buzzards are territorial, we found that 39% foraged within 1 km of the nest during their first winter, presumably within their parents' home range. Most (72%) of those that did not disperse were recorded making brief excursions during August and September, before opting for a “stay-at-home” strategy. There was no significant difference between the sexes in the tendency to make excursions or disperse, but females dispersed further than males. Buzzards which dispersed early tended to settle significantly farther from their nests than did late dispersers. Long-term radio-tracking has shown that 72% of the dispersing birds returned towards their natal area in the following breeding season. Such philopatry may be an important hindrance to avian recolonization following local extinctions.

David Baines - One of the best experts on this subject based on the ideXlab platform.

  • measures of predator diet alone may underestimate the collective impact on prey common buzzard Buteo Buteo consumption of economically important red grouse lagopus lagopus scotica
    PLOS ONE, 2019
    Co-Authors: Richard M Francksen, Sonja C Ludwig, David Baines, Nicholas J Aebischer, Mark J Whittingham
    Abstract:

    : Human-wildlife conflicts often centre on economic loss caused by wildlife. Yet despite being a major issue for land-managers, estimating total prey losses to predation can be difficult. Estimating impacts of protected wildlife on economically important prey can also help management decisions to be evidence-led. The recovery in population and range of common buzzards Buteo Buteo in Britain has brought them into conflict with some gamebird interests. However, the magnitude of any impact is poorly understood. We used bioenergetics models that combine measures of buzzard abundance from field surveys with diets assessed by using cameras at nests, prey remains and pellet analysis, to estimate their impact on red grouse Lagopus lagopus scotica on a large (115 km2) moor managed for red grouse shooting in Scotland. Whilst grouse consumption by individual buzzards was lower than previous estimates for other raptor species present on our study site, total consumption could be greater given an estimated 55-73 buzzards were present on the study site year-round. Averaging across diet assessment methods, consumption models estimated that during each of three breeding seasons (April-July 2011-2013), the buzzards foraging on our study site consumed 73-141 adult grouse and 77-185 chicks (depending on year). This represented 5-11% of adult grouse present in April (22-67% of estimated adult mortality) and 2-5% of chicks that hatched (3-9% of estimated chick mortality). During two non-breeding seasons (August-March), consumption models using pellet analysis estimated that buzzards ate a total of 242-400 grouse, equivalent to 7-11% of those present at the start of August and 14-33% of estimated grouse mortality during the non-breeding season. Buzzard consumption of grouse has the potential to lead to non-trivial economic loss to grouse managers, but only if buzzards predated the grouse they ate, and if grouse mortality is additive to other causes.

  • numerical and functional responses of common buzzards Buteo Buteo to prey abundance on a scottish grouse moor
    Ibis, 2017
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, Staffan Roos, David Baines
    Abstract:

    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.

  • winter diet of common buzzards Buteo Buteo on a scottish grouse moor
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, David Baines
    Abstract:

    ABSTRACTCapsule: 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 occ...

  • assessing prey provisioned to common buzzard Buteo Buteo chicks a comparison of methods
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, David Baines
    Abstract:

    ABSTRACTCapsule: 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 overest...

Richard M Francksen - One of the best experts on this subject based on the ideXlab platform.

  • measures of predator diet alone may underestimate the collective impact on prey common buzzard Buteo Buteo consumption of economically important red grouse lagopus lagopus scotica
    PLOS ONE, 2019
    Co-Authors: Richard M Francksen, Sonja C Ludwig, David Baines, Nicholas J Aebischer, Mark J Whittingham
    Abstract:

    : Human-wildlife conflicts often centre on economic loss caused by wildlife. Yet despite being a major issue for land-managers, estimating total prey losses to predation can be difficult. Estimating impacts of protected wildlife on economically important prey can also help management decisions to be evidence-led. The recovery in population and range of common buzzards Buteo Buteo in Britain has brought them into conflict with some gamebird interests. However, the magnitude of any impact is poorly understood. We used bioenergetics models that combine measures of buzzard abundance from field surveys with diets assessed by using cameras at nests, prey remains and pellet analysis, to estimate their impact on red grouse Lagopus lagopus scotica on a large (115 km2) moor managed for red grouse shooting in Scotland. Whilst grouse consumption by individual buzzards was lower than previous estimates for other raptor species present on our study site, total consumption could be greater given an estimated 55-73 buzzards were present on the study site year-round. Averaging across diet assessment methods, consumption models estimated that during each of three breeding seasons (April-July 2011-2013), the buzzards foraging on our study site consumed 73-141 adult grouse and 77-185 chicks (depending on year). This represented 5-11% of adult grouse present in April (22-67% of estimated adult mortality) and 2-5% of chicks that hatched (3-9% of estimated chick mortality). During two non-breeding seasons (August-March), consumption models using pellet analysis estimated that buzzards ate a total of 242-400 grouse, equivalent to 7-11% of those present at the start of August and 14-33% of estimated grouse mortality during the non-breeding season. Buzzard consumption of grouse has the potential to lead to non-trivial economic loss to grouse managers, but only if buzzards predated the grouse they ate, and if grouse mortality is additive to other causes.

  • numerical and functional responses of common buzzards Buteo Buteo to prey abundance on a scottish grouse moor
    Ibis, 2017
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, Staffan Roos, David Baines
    Abstract:

    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.

  • winter diet of common buzzards Buteo Buteo on a scottish grouse moor
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, David Baines
    Abstract:

    ABSTRACTCapsule: 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 occ...

  • assessing prey provisioned to common buzzard Buteo Buteo chicks a comparison of methods
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, David Baines
    Abstract:

    ABSTRACTCapsule: 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 overest...

Mark J Whittingham - One of the best experts on this subject based on the ideXlab platform.

  • measures of predator diet alone may underestimate the collective impact on prey common buzzard Buteo Buteo consumption of economically important red grouse lagopus lagopus scotica
    PLOS ONE, 2019
    Co-Authors: Richard M Francksen, Sonja C Ludwig, David Baines, Nicholas J Aebischer, Mark J Whittingham
    Abstract:

    : Human-wildlife conflicts often centre on economic loss caused by wildlife. Yet despite being a major issue for land-managers, estimating total prey losses to predation can be difficult. Estimating impacts of protected wildlife on economically important prey can also help management decisions to be evidence-led. The recovery in population and range of common buzzards Buteo Buteo in Britain has brought them into conflict with some gamebird interests. However, the magnitude of any impact is poorly understood. We used bioenergetics models that combine measures of buzzard abundance from field surveys with diets assessed by using cameras at nests, prey remains and pellet analysis, to estimate their impact on red grouse Lagopus lagopus scotica on a large (115 km2) moor managed for red grouse shooting in Scotland. Whilst grouse consumption by individual buzzards was lower than previous estimates for other raptor species present on our study site, total consumption could be greater given an estimated 55-73 buzzards were present on the study site year-round. Averaging across diet assessment methods, consumption models estimated that during each of three breeding seasons (April-July 2011-2013), the buzzards foraging on our study site consumed 73-141 adult grouse and 77-185 chicks (depending on year). This represented 5-11% of adult grouse present in April (22-67% of estimated adult mortality) and 2-5% of chicks that hatched (3-9% of estimated chick mortality). During two non-breeding seasons (August-March), consumption models using pellet analysis estimated that buzzards ate a total of 242-400 grouse, equivalent to 7-11% of those present at the start of August and 14-33% of estimated grouse mortality during the non-breeding season. Buzzard consumption of grouse has the potential to lead to non-trivial economic loss to grouse managers, but only if buzzards predated the grouse they ate, and if grouse mortality is additive to other causes.

  • numerical and functional responses of common buzzards Buteo Buteo to prey abundance on a scottish grouse moor
    Ibis, 2017
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, Staffan Roos, David Baines
    Abstract:

    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.

  • winter diet of common buzzards Buteo Buteo on a scottish grouse moor
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, Sonja C Ludwig, David Baines
    Abstract:

    ABSTRACTCapsule: 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 occ...

  • assessing prey provisioned to common buzzard Buteo Buteo chicks a comparison of methods
    Bird Study, 2016
    Co-Authors: Richard M Francksen, Mark J Whittingham, David Baines
    Abstract:

    ABSTRACTCapsule: 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 overest...