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Oliver Kruger - One of the best experts on this subject based on the ideXlab platform.
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Mesopredator release by an emergent superpredator: A natural experiment of predation in a three level guild. PLoS One. 2010; 5(12):e15229. doi
2016Co-Authors: Oliver Kruger, Nayden ChakarovAbstract:Background: Intraguild predation (IGP) is widespread but it is often neglected that guilds commonly include many layers of dominance within. This could obscure the effects of IGP making unclear whether the intermediate or the bottom mesopredator will bear higher costs from the emergence of a new top predator. Methodology/Principal Findings: In one of the most extensive datasets of avian IGP, we analyse the impact of recolonization of a superpredator, the eagle owl Bubo bubo on breeding success, territorial dynamics and population densities of two mesopredators, the northern Goshawk Accipiter gentilis and its IG prey, the common buzzard Buteo buteo. The data covers more than two decades and encompass three adjacent plots. Eagle owls only recolonized the central plot during the second decade, thereby providing a natural experiment. Both species showed a decrease in standardized reproductive success and an increase in brood failure within 1.5 km of the superpredator. During the second decade, territory dynamics of Goshawks was significantly higher in the central plot compared to both other plots. No such pattern existed in buzzards. Goshawk density in the second decade decreased in the central plot, while it increased in both other plots. Buzzard density in the second decade rapidly increased in the north, remained unchanged in the south and increased moderately in the center in a probable case of mesopredator release. Conclusions/Significance: Our study finds support for top-down control on the intermediate mesopredator and both top
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analysis of nest occupancy and nest reproduction in two sympatric raptors common buzzard buteo buteo and Goshawk accipiter gentilis
Ecography, 2002Co-Authors: Oliver KrugerAbstract:Nest site selection can have important fitness consequences in birds. I analysed the habitat characteristics of 392 nests of two sympatric raptor species (common buzzard Buteo buteo and Goshawk Accipiter gentilis) in Germany and their relation to nest occupation rate and nest reproductive success. For common buzzard, multivariate models explained only small proportions of the variance in nest occupation rate and nest reproductive success (13-19%). Important variables related to nest occupation rate were human disturbances, intra- and interspecific neighbour density, the amount of forested area and nest tree crown cover. Variables related to nest site reproductive success also included human disturbance, intra- and interspecific neighbour density and nest tree crown cover as well as nest distance to the nearest forest edge. In contrast, models for the Goshawk explained a much higher proportion of the variation in nest occupation rate and nest reproductive success (41-43%). Important variables related to nest occupation rate were the remoteness of the nest site and direct human disturbance. Variables related to nest site reproductive success were remoteness of the nest site and good hunting habitat. Goshawks seem to be more sensitive to human disturbance than buzzards. A multiple discriminant analysis showed that nest site characteristics substantially overlapped between the species and there is a good evidence that competition for optimal nest sites occurs. Thus, buzzards might be constrained by the dominant Goshawk in their nest site selection.
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interactions between common buzzard buteo buteo and Goshawk accipiter gentilis trade offs revealed by a field experiment
Oikos, 2002Co-Authors: Oliver KrugerAbstract:I examined the behavioural interactions between common buzzard Buteo buteo and Goshawk Accipiter gentilis and their effects on buzzard breeding success and brood defence with a two-year field experiment using dummies and playback calls. A priori I showed through an extensive nest site analysis that there is considerable nesting habitat overlap between the two species and hence potential for interspecific competition for prime nesting habitat. Buzzards had a significantly lower breeding success when presented with a Goshawk dummy compared to control broods but there was no effect of buzzard dummies on reproductive success. Buzzards failing with their breeding attempt tended to select another nest site while successful buzzards more frequently used the same nest again. Buzzard pairs were less often attacked by common crows Corvus corone while exposed to Goshawk dummies compared to buzzard dummies. The decision to desert a nest seems to be a trade-off between predation risk on the one hand and protection against crows on the other. Goshawks proved far more aggressive against an intraspecific dummy than buzzards. Buzzards adjusted their level of brood defence against both intra- and interspecific dummies according to the age of offspring but not offspring number, with an increasing brood defence level with increasing offspring age. Thus the behaviour of buzzards towards Goshawks is a result of a complex system of trade-offs between predation risk, competition for prime nesting habitat and protection from crows on which brood value acts as a temporal modifier.
J M Fernandezpereira - One of the best experts on this subject based on the ideXlab platform.
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breeding habitat preferences and reproductive success of northern Goshawk accipiter gentilis in exotic eucalyptus plantations in southwestern europe
Forest Ecology and Management, 2018Co-Authors: Gonzalo Garciasalgado, Salvador Rebollo, Lorenzo Perezcamacho, Sara Martinezhesterkamp, E De La Montana, R Domingomunoz, Jaime Madrigalgonzalez, J M FernandezpereiraAbstract:Abstract With ongoing degradation of natural forests and spread of forest plantations, plantations must play an increasingly important role in biodiversity conservation. Study of habitat selection and reproductive success of surrogate species in plantations can guide forest management decisions for increasing biodiversity. In this paper we studied the suitability of exotic Eucalyptus plantations managed at low intensity in northwestern Spain as breeding habitat for Northern Goshawk (Accipiter gentilis), a top predator frequently considered a surrogate species in conservation. Goshawks showed high breeding density, high reproductive success and a regular spatial distribution of nesting territories. Territoriality was the most important determinant of habitat selection. Goshawks selected extra-mature Eucalyptus trees in areas of high structural complexity (high tree density, tree species richness, and number of tree strata) in the most heterogeneous forest stands (old-mixed Eucalyptus). Reproductive success decreased with increasing local density of breeding pairs, but reproductive success was not related to structural characteristics of nest stands. The studied plantations provided a suitable breeding habitat for Goshawks. The birds preferred to nest in large Eucalyptus trees with appropriate structure in their immediate surroundings. The strong preference of Goshawks for structurally mature forest patches may make them useful as a surrogate species for assessing the ability of forest management practices to promote overall biodiversity in exotic Eucalyptus plantations exploited at low intensity.
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evaluation of trail cameras for analyzing the diet of nesting raptors using the northern Goshawk as a model
PLOS ONE, 2015Co-Authors: Gonzalo Garciasalgado, Salvador Rebollo, Alberto Navarro, Lorenzo Perezcamacho, Sara Martinezhesterkamp, J M FernandezpereiraAbstract:Diet studies present numerous methodological challenges. We evaluated the usefulness of commercially available trail-cameras for analyzing the diet of Northern Goshawks (Accipiter gentilis) as a model for nesting raptors during the period 2007–2011. We compared diet estimates obtained by direct camera monitoring of 80 nests with four indirect analyses of prey remains collected from the nests and surroundings (pellets, bones, feather-and-hair remains, and feather-hair-and-bone remains combined). In addition, we evaluated the performance of the trail-cameras and whether camera monitoring affected Goshawk behavior. The sensitivity of each diet-analysis method depended on prey size and taxonomic group, with no method providing unbiased estimates for all prey sizes and types. The cameras registered the greatest number of prey items and were probably the least biased method for estimating diet composition. Nevertheless this direct method yielded the largest proportion of prey unidentified to species level, and it underestimated small prey. Our trail-camera system was able to operate without maintenance for longer periods than what has been reported in previous studies with other types of cameras. Initially Goshawks showed distrust toward the cameras but they usually became habituated to its presence within 1–2 days. The habituation period was shorter for breeding pairs that had previous experience with cameras. Using trail-cameras to monitor prey provisioning to nests is an effective tool for studying the diet of nesting raptors. However, the technique is limited by technical failures and difficulties in identifying certain prey types. Our study also shows that cameras can alter adult Goshawk behavior, an aspect that must be controlled to minimize potential negative impacts.
Michael Lierz - One of the best experts on this subject based on the ideXlab platform.
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high prevalence of sarcocystis calchasi sporocysts in european accipiter hawks
Veterinary Parasitology, 2011Co-Authors: Philipp Olias, Lena Olias, Michael Lierz, Jurgen Krucken, Achim D GruberAbstract:The emerging Sarcocystis calchasi induces a severe and lethal central nervous disease in its intermediate host, the domestic pigeon (Columba livia f. domestica). Experimental studies have identified the Northern Goshawk (Accipiter g. gentilis) as final host. Phylogenetically closely related European sparrowhawks (Accipiter n. nisus) and wood pigeons (Columba palumbus) have been found to harbor genetically closely related Sarcocystis spp. However, data on the prevalence and potential interspecies occurrence of these parasites are lacking. Here, we report that European Accipiter hawks (Accipitrinae) are highly infected with S. calchasi, S. columbae and Sarcocystis sp. ex A. nisus in their small intestine. Thirty-one of 50 (62%) Northern Goshawks necropsied during 1997-2008 were positive for S. calchasi in a newly established species-specific semi-nested PCR assay based on the first internal transcribed spacer region. Unexpectedly, 14 of 20 (71.4%) European sparrowhawks tested also positive. In addition, birds of both species were found to be infested with S. columbae and an, as yet, unnamed Sarcocystis sp. recently isolated from European sparrowhawks. These findings raise new questions about the host specificity of S. calchasi and its high virulence in domestic pigeons, since sparrowhawks only rarely prey on pigeons. Notably, isolated sporocysts from both infected Accipiter spp. measured 8 μm × 11.9 μm, precluding a preliminary identification of S. calchasi in feces of Accipiter hawks based on morphology alone. Importantly, three of four Northern Goshawks used in falconry tested positive for S. calchasi. In conclusion, the results indicate that both European Accipter spp. in Germany serve as natural final hosts of S. calchasi and suggest that falconry and pigeon sport may serve as risk factors for the spread of this pathogen in domestic pigeons.
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Unusual Biphasic Disease in Domestic Pigeons (Columba livia f. domestica) Following Experimental Infection with Sarcocystis calchasi
Avian Diseases, 2010Co-Authors: Philipp Olias, Andrea Kohls, Hafez M Hafez, Achim D Gruber, Michael LierzAbstract:Abstract A novel Sarcocystis species has recently been reported in the domestic pigeon (Columba livia f. domestica) as intermediate host, causing severe central nervous signs similar to Paramyxovirus-1 or Salmonella Typhimurium var. cop. infection. Transmission of the parasite via the northern Goshawk (Accipiter gentilis) as definitive host has been established. Experimental infection of domestic pigeons with sporocysts excreted by experimentally infected northern Goshawks reproduced the natural infection in the pigeon, proving the causative role of the parasite in the disease. Here, we describe in greater detail the course of the fulminant biphasic disease depending on the infectious dose. Pigeons infected with 103 or 104 sporocysts showed clinical signs of polyuria and apathy around 10–11 days postinfection (dpi) and sudden neurological signs 51–57 dpi as a second phase of disease. Pigeons infected with higher doses died within 7–12 dpi, also showing polyuria and apathy but without nervous signs. At nec...
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sarcocystis calchasi sp nov of the domestic pigeon columba livia f domestica and the northern Goshawk accipiter gentilis light and electron microscopical characteristics
Parasitology Research, 2010Co-Authors: Philipp Olias, Hafez M Hafez, Achim D Gruber, Heinz Mehlhorn, Michael LierzAbstract:A novel highly pathogenic Sarcocystis species has been shown to cycle between the Northern Goshawk (Accipiter gentilis) as definitive host and the domestic pigeon (Columba livia f. domestica) as intermediate host. However, genetically based characteristics are only available from very few bird-infecting Sarcocystis species. We therefore further characterised morphological properties of this protozoan in both hosts. Using light and electron microscopy, oocysts and sporocysts as well as schizonts and sarcocysts were characterised and compared with available morphological features of previously reported Sarcocystis species of Northern Goshawks, Columbidae and genetically closely related species of other avian hosts. Sporocysts shed from day 6 on after experimental infection by the Northern Goshawk were of ovoid appearance (11.9 × 7.9 μm). Ultrastructurally, schizonts of all developmental stages were found in the liver, spleen and next to or in endothelial cells of various organs of domestic pigeons 7 to 12 days after experimental infection. The cyst wall surface of slender sarcocysts (1 to 2 mm in length and 20 to 50 μm in width) was smooth and lacked protrusions. Cystozoites were lancet-shaped and measured 7.5 × 1.5 μm in Giemsa stain smears. The morphological findings, when combined with data of experimental infection and genetic studies, convergently indicate that the recently discovered Sarcocystis species represents a new species. We therefore propose to name this parasite Sarcocystis calchasi species nova.
J J Herholdt - One of the best experts on this subject based on the ideXlab platform.
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the social system of the pale chanting Goshawk melierax canorus monogamy v polyandry and delayed dispersal
Ibis, 2008Co-Authors: G Malan, Timothy M Crowe, R Biggs, J J HerholdtAbstract:The social organization and reproductive strategy of the Pale Chanting Goshawk Melierax canorus were investigated in four southern African study areas. Territories supporting adults additional to the breeding pair were observed in two study areas. Within one of these areas, these additional adults were either non-breeders staying in their natal territory but actively excluded from the nesting area during the breeding season or a male cobreeder participating fully in reproductive activities with the breeding pair. Polyandrous trios were, however, observed in only one vegetation type in this area, Broken Veld. The annual number of offspring fledged per group did not differ significantly between vegetation types nor between polyandrous trios and monogamous pairs within Broken Veld. Pale Chanting Goshawks lay predominantly two-egg clutches. In 2 out of 5 years, breeding groups succeeded in laying, hatching and even fledging a second brood of young after successfully fledging their first brood. Double brooding occurred more frequently in Broken Veld and most frequently in polyandrous trios in this vegetation type. To accommodate their relatively long breeding cycle (>115 days) in this temperate study area with its limiting summer breeding period, double-brooding Pale Chanting Goshawks laid the first clutch in midwinter and the second, on average, 24 days after the offspring from the first brood left the nest.
Philipp Olias - One of the best experts on this subject based on the ideXlab platform.
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high prevalence of sarcocystis calchasi sporocysts in european accipiter hawks
Veterinary Parasitology, 2011Co-Authors: Philipp Olias, Lena Olias, Michael Lierz, Jurgen Krucken, Achim D GruberAbstract:The emerging Sarcocystis calchasi induces a severe and lethal central nervous disease in its intermediate host, the domestic pigeon (Columba livia f. domestica). Experimental studies have identified the Northern Goshawk (Accipiter g. gentilis) as final host. Phylogenetically closely related European sparrowhawks (Accipiter n. nisus) and wood pigeons (Columba palumbus) have been found to harbor genetically closely related Sarcocystis spp. However, data on the prevalence and potential interspecies occurrence of these parasites are lacking. Here, we report that European Accipiter hawks (Accipitrinae) are highly infected with S. calchasi, S. columbae and Sarcocystis sp. ex A. nisus in their small intestine. Thirty-one of 50 (62%) Northern Goshawks necropsied during 1997-2008 were positive for S. calchasi in a newly established species-specific semi-nested PCR assay based on the first internal transcribed spacer region. Unexpectedly, 14 of 20 (71.4%) European sparrowhawks tested also positive. In addition, birds of both species were found to be infested with S. columbae and an, as yet, unnamed Sarcocystis sp. recently isolated from European sparrowhawks. These findings raise new questions about the host specificity of S. calchasi and its high virulence in domestic pigeons, since sparrowhawks only rarely prey on pigeons. Notably, isolated sporocysts from both infected Accipiter spp. measured 8 μm × 11.9 μm, precluding a preliminary identification of S. calchasi in feces of Accipiter hawks based on morphology alone. Importantly, three of four Northern Goshawks used in falconry tested positive for S. calchasi. In conclusion, the results indicate that both European Accipter spp. in Germany serve as natural final hosts of S. calchasi and suggest that falconry and pigeon sport may serve as risk factors for the spread of this pathogen in domestic pigeons.
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Unusual Biphasic Disease in Domestic Pigeons (Columba livia f. domestica) Following Experimental Infection with Sarcocystis calchasi
Avian Diseases, 2010Co-Authors: Philipp Olias, Andrea Kohls, Hafez M Hafez, Achim D Gruber, Michael LierzAbstract:Abstract A novel Sarcocystis species has recently been reported in the domestic pigeon (Columba livia f. domestica) as intermediate host, causing severe central nervous signs similar to Paramyxovirus-1 or Salmonella Typhimurium var. cop. infection. Transmission of the parasite via the northern Goshawk (Accipiter gentilis) as definitive host has been established. Experimental infection of domestic pigeons with sporocysts excreted by experimentally infected northern Goshawks reproduced the natural infection in the pigeon, proving the causative role of the parasite in the disease. Here, we describe in greater detail the course of the fulminant biphasic disease depending on the infectious dose. Pigeons infected with 103 or 104 sporocysts showed clinical signs of polyuria and apathy around 10–11 days postinfection (dpi) and sudden neurological signs 51–57 dpi as a second phase of disease. Pigeons infected with higher doses died within 7–12 dpi, also showing polyuria and apathy but without nervous signs. At nec...
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sarcocystis calchasi sp nov of the domestic pigeon columba livia f domestica and the northern Goshawk accipiter gentilis light and electron microscopical characteristics
Parasitology Research, 2010Co-Authors: Philipp Olias, Hafez M Hafez, Achim D Gruber, Heinz Mehlhorn, Michael LierzAbstract:A novel highly pathogenic Sarcocystis species has been shown to cycle between the Northern Goshawk (Accipiter gentilis) as definitive host and the domestic pigeon (Columba livia f. domestica) as intermediate host. However, genetically based characteristics are only available from very few bird-infecting Sarcocystis species. We therefore further characterised morphological properties of this protozoan in both hosts. Using light and electron microscopy, oocysts and sporocysts as well as schizonts and sarcocysts were characterised and compared with available morphological features of previously reported Sarcocystis species of Northern Goshawks, Columbidae and genetically closely related species of other avian hosts. Sporocysts shed from day 6 on after experimental infection by the Northern Goshawk were of ovoid appearance (11.9 × 7.9 μm). Ultrastructurally, schizonts of all developmental stages were found in the liver, spleen and next to or in endothelial cells of various organs of domestic pigeons 7 to 12 days after experimental infection. The cyst wall surface of slender sarcocysts (1 to 2 mm in length and 20 to 50 μm in width) was smooth and lacked protrusions. Cystozoites were lancet-shaped and measured 7.5 × 1.5 μm in Giemsa stain smears. The morphological findings, when combined with data of experimental infection and genetic studies, convergently indicate that the recently discovered Sarcocystis species represents a new species. We therefore propose to name this parasite Sarcocystis calchasi species nova.
