I’ve been focusing on migrants on my blog over the past couple of weeks partly because it is spring, partly because they are in trouble but principally because of the heightened profile that Chris Packham has given to impact of spring hunting in Malta.
The thing about migrants is that they, perhaps more than any other group, show the interconnected and fragile nature of our planet. The sight of our first swallow, a cuckoo calling or the song of a nightingale are hard-wired into national consciousness - but their survival requires international cooperation and enforcing laws here and across Europe.
I am focusing on turtle dove because, as I said in my blog on Sunday (here), it is probably our most rapidly declining bird (94% in 40 years; 77% in the last decade) -.and their demise is echoing the extinction of the passenger pigeon in North America a century ago (the subject of a forthcoming book by my predecessor, Mark Avery, see here).
It is time to act.
If we want to reverse the declines in our migrants, we have to do what we can to address all the problems they face throughout the flyway with a partners such as the BTO and Birdlife International.
As we know, turtle dove is hunted in huge numbers in the Mediterranean (see Monday’s blog here) but as I will profile later this week, it is also subject to habitat destruction throughout their flyway and getting the habitat right in its breeding grounds here in the UK is equally important.
Perhaps less well known is that turtle dove is also prone to disease – the topic of today’s blog.
Scientists at the RSPB, working with colleagues from the University of Leeds, have discovered that a very high proportion (95%) of adult and nestling turtle doves sampled in East Anglia were infected by the Trichomonas parasite, which can lead to the disease trichomonosis. This parasite is common among pigeons and doves, is a serious threat to the endangered endemic Mauritian pink pigeon, and has also been implicated in the decline of greenfinch populations across the UK. And it is not pleasant: the parasite causes lesions in the throat of infected birds preventing them from feeding and leading to death by starvation.
Although the infection rate is very high, relatively few of the birds actually showed clinical signs. All of those that did died of the disease, but it remains uncertain what effect the parasite may be having on the other infected birds. There were more birds showing clinical signs in 2012, a very wet summer in which many of our breeding birds suffered poor productivity. This raises the possibility that the effects of the parasite may be exacerbated by food stress, a potentially interesting link to the reduction in food availability or change in food quality, due to a reduction of seeds of arable flowers caused by changing farming practices, that have occurred over the period of the turtle dove’s decline. I shall return to this in tomorrow’s blog.
There does indeed appear to be a link between infection rates and food availability. Birds were more likely to be infected on farms that provided supplementary food for gamebirds, which also attracts pigeons and doves. This may be a similar problem as faced by greenfinches, where transmission of the parasite occurs at garden feeders that attract many birds. In support of this idea, a single red-legged partridge that also died from trichomonosis was found to carry the same strain of the parasite as the doves, also raising the possibility that the disease can be transmitted between doves / pigeons and gamebirds.
So, our researchers have begun to learn a lot about disease in turtle doves, but many questions remain. What effect is the parasite having when a bird has no clinical signs? Is it the same strain of the parasite that is found in greenfinches (early evidence suggests that may be a relationship)? And perhaps most importantly, is the mortality associated with the disease contributing to the continued decline of this iconic species?
We need to find answers to these questions and then identify and roll out solutions – something our scientists excel at.
Tomorrow, I shall return to the challenges turtle doves face in finding enough food on their breeding grounds
Another example of very excellent work by the RSPB on this important subject of disease control.