Starlings in mass drownings leave scientists baffled

Starlings in mass drownings have left scientists baffled. Groups of 10 or more starlings have been found drowned across the UK, prompting researchers to investigate these highly unusual and bizarre occurrences.

A team of British scientists, led by the Zoological Society of London (ZSL), are trying to find out what the cause of this unexpected recurrent mass mortality of Common starlings (Sturnus vulgaris) is. They have published details of their research so far in the academic journal Scientific Reports.

Dying from drowning is comparatively rare among wild birds, and when it does happen it generally involves just one bird and not groups of them. Lead author, Dr. Becki Lawson, a wildlife veterinarian at ZSL, says starlings have been seen drowned in groups of ten or more.

Starlings drowned en masseSeveral juvenile starlings found dead in a plastic bucket and which likely drowned. (Image: Scientific Reports)

Dr. Lawson and colleagues studied twelve separate incidents of mass starling drownings between 1993 and 2013 – on ten of these occasions, over 10 birds drowned.

Only juvenile birds drowned

In every case, the unfortunate victims were juvenile birds just a few months old, that died in the spring or early summer months.



The authors said they found no evidence of any underlying disease as a cause of death in any of the cases.

Dr. Lawson said:

“Drowning appears to be a more common cause of death amongst younger birds, as they may be inexperienced in identifying water hazards. This combined with the fact that starlings are a highly social species could potentially explain why multiple birds drown together.”

“Members of the public from around Great Britain have been instrumental in bringing this unexpected cause of starling mortality to our attention by reporting these incidents. With starling numbers declining in general across the UK, we need to learn more about how and where these phenomena happen, in order to better understand why.”

Starlings and blackbirds drownedDrowning appears to be an unexpected recurrent cause of mass mortality of Common starlings. (Image: Scientific Reports)

The starling is a Red-Listed species

Co-author, Rob Robinson, Associate Director of Research at the British Trust for Ornithology (BTO), commented:

“Starlings are a Red-listed species in the UK, under threat from issues including loss of nesting sites and a lack of insect food sources – so much so that their population has declined 79 per cent in the past 25 years.”

“Whilst drowning is an unexpected cause of death, it’s not thought to be a conservation threat as – fortunately – these incidents are currently relatively rare. However, we still need to better understand factors such as disease that might be contributing to this decline. We would therefore ask people to keep up the good work by reporting incidents of starling death, whatever the apparent cause, via the Garden Wildlife Health website.”

Perhaps adding ramps may help

Water is a crucial resource for wild birds, especially during the summer months. People are asked to continue providing bird baths and ponds as a way to support garden wildlife.

Experts are recommending, however, that people add a sloping exit or ramp to water features, in order to make it easier for birds and other animals get to and exit water sources.

People across the United Kingdom who see a dead or sick bird, or any other animal in their gardens, can help researchers learn more about what the cause was by reporting these incidents in the project website.

Citation: Drowning is an apparent and unexpected recurrent cause of mass mortality of Common starlings (Sturnus vulgaris),” Becki Lawson, J. Paul Duff, Katie M. Beckmann, Julian Chantrey, Kirsi M. Peck, Richard M. Irvine, Robert A. Robinson & Andrew A. Cunningham. Scientific Reports 5, Article number: 1702. 25 November, 2015. DOI: 10.1038/srep17020.

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