Causes, temporal trends, and the effects of urbanization on admissions of wild raptors to rehabilitation centers in England and Wales

Abstract

Data from wildlife rehabilitation centers (WRCs) can provide on-the-ground records of causes of raptor morbidity and mortality, allowing threat patterns to be explored throughout time and space. We provide an overview of native raptor admissions to four WRCs in England and Wales, quantifying the main causes of morbidity and mortality, trends over time, and associations between threats and urbanization between 2001 and 2019. Throughout the study period, 14 raptor species were admitted totalling 3305 admission records. The Common Buzzard (Buteo buteo; 31%) and Tawny Owl (Strix aluco; 29%) were most numerous. Relative to the proportion of breeding individuals in Britain and Ireland, Peregrine Falcons (Falco peregrinus), Little Owls (Athene noctua), and Western Barn Owls (Tyto alba) were over-represented in the admissions data by 103%, 73%, and 69%, respectively. Contrastingly Northern Long-eared Owls (Asio otus), Western Marsh Harriers (Circus aeruginosus), and Merlin (Falco columbarius) were under-represented by 187%, 163%, and 126%, respectively. Across all species, vehicle collisions were the most frequent anthropogenic admission cause (22%), and orphaned young birds (10%) were most frequent natural cause. Mortality rate was highest for infection/parasite admissions (90%), whereas orphaned birds experienced lowest mortality rates (16%). For one WRC, there was a decline in admissions over the study period. Red Kite (Milvus milvus) admissions increased over time, whereas Common Buzzard and Common Kestrel admissions declined. There were significant declines in the relative proportion of persecution and metabolic admissions and an increase in orphaned birds. Urban areas were positively associated with persecution, building collisions, and unknown trauma admissions, whereas vehicle collisions were associated with more rural areas. Many threats persist for raptors in England and Wales, however, have not changed substantially over the past two decades. Threats associated with urban areas, such as building collisions, may increase over time in line with human population growth and subsequent urban expansion.

Causes of Raptor Admission to the Wildlife Rehabilitation Centre in Abruzzo (Central Italy) from 2005–2016

“…The low prevalence of infectious disease and toxicosis found in this study could be explained by the presence of multiple morbidity and mortality factors. These results were consistent with similar studies [ 15 , 21 , 24 , 25 , 28 , 56 ] but in contrast with those reported in Morishita et al [ 13 ], who found that 30.3% (124/409) of the examined raptors had infectious or toxic effects. However, in this last study, only dead raptors presented for necropsy were analyzed, so neither nestling nor starvation of birds of prey were considered.…”

“…It was therefore chosen to keep information on the anatomical location of the trauma and not on its origin. This choice does not allow a full comparison of the origins of the trauma with other published studies; however, it was possible to confirm that the traumatic diagnosis is the main cause of admission for birds of prey in a WRC [ 13 , 14 , 15 , 26 , 27 , 28 , 40 , 44 , 45 , 46 , 47 , 48 ]. These results are, however, in contrast with finding trauma in only 5% of 92 free-living British Kestrels ( Falco tinnunculus ) in another study [ 49 ].…”

“…Connor T.P. et al reported that urban areas were positively associated with persecution, building collisions, and unknown trauma admissions, whereas vehicle collisions were associated with more rural areas [ 28 ].…”

“…The rehabilitation and release of admitted birds to the wild can help buffer the negative effects of anthropogenic and non-human activities, especially for those species that have conservation concerns [ 28 ]. Further study needs to be conducted to improve and define predictive indicators of survival and the possibility of release into the wild as reported and emphasized in other studies [ 70 , 71 , 72 ].…”

“…However, only a few studies on the causes of morbidity in wild raptors are available for the Italian territory [ 22 ]. Furthermore, long-term epidemiologic studies of wild raptor medical conditions spanning more than a decade are scarce worldwide [ 11 , 12 , 21 , 23 , 24 , 25 , 26 , 27 , 28 ]. Threats to raptors come mainly from humans and include habitat loss, climate change, poisoning, collisions, electrocutions, and deliberate capture or culling.…”