The mystery of missing starlings

Starlings are a type of bird; they're found across the world and they're famous for murmurations - you might have seen video footage where thousands of them flock together in a mass acrobatic routine. But the numbers of these birds have nosedived, and recently, drowning has emerged as one mysterious cause of death among the species. Graihagh Jackson has been looking into the phenomenon...

Graihagh - This is the song of a common starling.  Starlings are found across the UK.  You might recognise them in fact.  They look like they've been dipped in oil as their glossy black coats shimmer with metallic greens, and blues, and purples and, to top it off, it looks likes someone's taken a fountain pen and flicked white ink all over them.  Thier plumage isn't the only beautiful think about them though. I showed the Naked Scientist in the office a video of what's known as a 'starling murmuration.'

Rob - Sometimes, you can just stumble on them.  In Norwich, for instance, I was waiting for the train one evening and above the station I suddenly saw three or four thousand starlings flying over my head which was really quite magical.

Graihagh - Rob Robbins there, from the British Trust of Ornithology.

Rob - Murmurations occur just before dark and the starlings have been out in the fields; they've been foraging probably on leather jackets, earth worms and...

Graihagh - Leather jackets?

Rob - Leather jackets, which are baby crane flies...

Graihagh - Okay, not the item of clothing you wear?

Rob - Not the item of clothing that you wear - no.  So they've been foraging hard all day and basically at night they gather together in big roosts.  And some of these roosts can be 10, 20 50 thousand birds or sometimes even larger and when you have all of these birds flying up and down together it can be quite a spectacle.

Graihagh - Although they do flock on mass, these birds are actually declining?

Rob - Yes, they have been in terrible trouble over the last 25 years.  They've declined by something like 80 or 90% over the last 25 years.

Graihagh - 80 or 90% is a frightening rate of decline.  But why is this happening?  A recent report found drowning as a mysterious cause of mass mortality among starlings.  Drowning is an unusual cause of death as Becki Lawson from the Zoological Society of London explained.

Becki - No, drowning's certainly not a common cause of death in wild birds, but it certainly has been recorded, in particular in birds of prey.

Graihagh - So why have starlings been drowning?  Becki did a post-mortem to see if there were any signs of toxins, viruses or parasites that might have caused them to become confused or extra thirsty.

Becki - So when we undertake a post-mortem we take a systematic approach.  We examine each of the body systems in turn - we look at them with the naked eye and we also take tissues and look at them under the microscope.

Graihagh - And in a suspected drowning, what would you be looking for?

Becki - Drownings are really quite a challenging diagnosis to make, particularly when we're dealing with wild animals when we're not able to examine them very soon after these events have occurred.  So it's a process of illumination, trying to look at all the findings together and exclude suggestions of important infectious disease or toxins and if none of those were present, as was the case here, we think that evidence points to them having drowned.

Graihagh - So there wasn't any evidence of anything in their blood or on the slides in their cells that suggested that it could have been poison that had made them drown?

Becki - We found no evidence of presence of any of the pesticides that were screened for.

Graihagh - And no virus either?

Becki - No, no viruses.

Graihagh - So what could have caused these birds to drown?

Becki - Well we think the cause is most likely related to the behaviour of starlings.  When we think of them, we often imagine them in groups and so if they were to enter a body of water together as a group, that might be the simple explanation of why the drown in multiple numbers.  And second, it's most commonly involved youngsters - juvenile birds - and so there's probably an element of juvenile inexperience in identifying these water hazards.

Graihagh - Are the numbers of these starlings drowning significant enough to be causing their decline?

Becki - No.  I don't think so.

Graihagh - If the numbers aren't high enough to be causing the starling decline, why are they declining?  Rob Robinson again.

Rob - I think there's a number of reasons for that and I think they fall into two main groups.  Many starlings are foraging in farmland habitats and there have been large scale changes in farming practice over the last 20 or 30 years, so there's less foraging habitat for starlings, and then I think also there are things going on in towns and cities.  And there's a couple of things going on there, one of which is in terms of people developing gardens and not leaving the weedy corners, and the other thing is starlings nest in halls. They are cavity nesters and traditionally they would have nested under the eaves of houses or in barns and, obviously, people prefer not to have birds scrabbling around in their loft spaces so they're blocking up the eaves and putting in plastic soffits.  So basically the starlings are being deprived of nesting opportunities as well.

Graihagh - Given that it's so many factors, how do you go about tackling that?

Rob - The BTO has been working quite hard to look at ways of influencing agricultural policy but I think practically people can do simple things by putting up nest boxes for a start and then you get to enjoy their antics without being disturbed at night.

Graihagh - Your own private display.

Rob - Indeed.