Tracking equipment could be harming wild birds, experts warn

Hi-tech tracking equipment that maps the lives of bird species appears to be damaging the health and welfare of the birds to which it is attached, wildlife experts have warned.

A study involving postmortems on red kites fitted with radio transmitters in England has aroused suspicions that the equipment could cause lesions and reduce the breeding prospects of those being tracked.

Natural England, the government's environmental body, and the British Trust for Ornithology, are so worried that they have issued new guidance for postmortems on wild birds in the hope of establishing the long-term effects of such equipment.

Bird-tracking programmes involving radio and satellite transmitters or GPS devices are becoming ever more popular with the public as well as researchers, while the reintroduction of red kites, once on the verge of extinction in England, has proved a remarkable success. Twenty-two years after the programme started, there are an estimated 1,000 breeding pairs.

The new concerns are raised in the Veterinary Record in a report by experts, including staff from the Zoological Society of London, and Natural England, and in an accompanying editorial. Since 2000, 180 red kites have undergone postmortems, one in 10 of which had been fitted with radio transmitters carried in harness backpacks. Four of these, which had carried the battery-operated equipment for between three and five years, had moderate to severe lesions, said the report. These probably led to the death of one bird and precipitated the deaths from other causes of the others, say the researchers. Two of the four had also reportedly failed to breed over preceding years although it was not known if the tracking equipment was a factor.

The report added that it was "reasonable to assume" that some cases of harness-associated disease in red kites had gone undetected. Those fitted with the tracking device were left to carry them after their batteries failed because recapture was deemed likely to further stress the birds. Tail-mounted transmitters, also used for tracking birds, do not last as long because they can only be fitted after birds have left their nests with tails fully grown and they fall off when feathers moult. No lesions were found in birds known to have carried such transmitters. This suggested that for short-term monitoring of less than a year, tail-mounted transmitters on birds could be preferable.

Rebecca Vaughan-Higgins, from the Zoological Society of London, who was involved in the study, said: "It is important that we consider both the costs and benefits of the use of harness-mounted radio transmitters and other tracking devices. Radio transmitters are used worldwide in avian species to study habitat use, mortality, migration, home range and physiology. In our own work, they have been valuable because free-living sick and dead red kites can be quickly detected, and health and post-mortem examinations carried out within a short period. The examination of fresh carcases increases the value of the information we can obtain on the threats to red kite health. For example, we have published evidence for harm due to lead poisoning in red kites and these findings allowed mitigation measures to be implemented to reduce the threat to these birds."

Separate from the red kites that had undergone postmorterms in the study, Vaughan-Higgins said that of 142 red kites fitted with harness-mounted transmitters between 2000 and 2009, only 12% have been found dead. She said: "Unless and until further long-term studies have been carried out it is not possible to determine whether the findings are a sign of a greater problem in kites. Studies on other birds fitted with these devices are also warranted because we do not know whether kites have a predisposition to develop these lesions in association with harnesses or whether other birds are at risk."

Ian Carter, a co-author of the report and an ornithologist for Natural England, told the Guardian: "Any time you add any kind of weight to a bird, it will have some kind of effect. It is important to keep that to a minimum."

The accompanying editorial by Andrew Dixon, of International Wildlife Consultants, in Carmarthen, Wales, said the study highlighted the need to "carefully consider the impacts of tagging methods" on birds of prey. The relative lack of previous research on the issue was "somewhat surprising, given the high profile of many bird tracking projects and the depth of public feeling in relation to animal welfare."

James Meikle

guardian.co.uk

http://www.guardian.co.uk/environment/2011/sep/20/tracking-equipment-birds-health