key: cord-0012026-qi6mh4ok
authors: Duff, J P; Richey, M; Holmes, J P; Bianco, C; Duff, K P; Lawson, B
title: Suspected collision trauma deaths in pied wagtails
date: 2020-06-13
journal: Vet Rec
DOI: 10.1136/vr.m2272
sha: 83a8825335ad38da42016bceac9371e34e413685
doc_id: 12026
cord_uid: qi6mh4ok

nan

THE APHA Diseases of Wildlife Scheme (DoWS) investigates mass deaths of wildlife as a priority and in October 2019 was called to investigate a report from the public of multiple pied wagtails (Motacilla alba) found dead or dying on the ground around the entrance (brightly lit from the interior) to a large building in the Midlands.

Outside the breeding season, pied wagtails often communally roost in trees in city centres and other brightly lit areas of human activity -roosting close to artificial light is unusual among British birds. 1 The roosts may comprise thousands of birds.

Nineteen wagtails were collected and four of these, some in first-year plumage, were submitted to the APHA Shrewsbury Veterinary Investigation Centre for examination. Postmortem examination revealed that the birds were in reasonably good body condition with haemorrhage in various tissues, including lungs and air sacs, indicative of blunt trauma. Avian influenza virus was not detected. Histopathological examination of multiple tissues revealed no evidence of other disease.

The building was visited on an evening five weeks after the incident was reported. Approximately 100 pied wagtails were found roosting in two trees at the building entrance with the greatest concentration of birds closest (within 2 m) to the brightest glazed area near the door. A single bird was on the ground. This individual was able to run and evade capture; however, it was unable to fly, suggesting that it was injured. Bird faeces were seen in a compact distribution on one window only, opposite the roost site.

Based on the findings of internal haemorrhage consistent with blunt trauma, exclusion of alternative diagnoses, the scene investigation, and the known attraction of this species to bright lights, we concluded that a flight error was the likely cause of fatal collisions against a window. We suggest that the birds collided in flight because they were seeking a roost site close to the light sources in the foyer but did not see the intervening windows, or they were dazzled by the lights as they flew into the nearest tree by the entrance.

The owners of the building have been advised on ways to try to prevent the losses, principally by using covers over the target windows at critical times of the year, to enable the birds to see the windows as solid structures and avoid them.

Due to their roosting preferences, deaths of pied wagtails around winter roosts are likely to recur. Flight and flocking places birds at risk of colliding, particularly if visual cues are obscured or misinterpreted, for Flight and flocking places birds at risk of colliding 

City roosts for pied wagtails

SAC Veterinary Services, wild birds

Suspected wild bird mortality in Britain due to stormy weather and hailstones

Weather and Bird Behaviour. 1983. T & AD Poyser

Suspected ethanol toxicity in juvenile blackbirds and redwings

Mass mortality of starlings roosting by a roadside

Mass mortality of starlings

Mass mortality of starlings in Somerset

Drowning is an apparent and unexpected recurrent cause of mass mortality of common starlings (Sturnus vulgaris)