New research published online today in the British Ecological Society’s Journal of Applied Ecology offers a way to more accurately estimate the size of bird populations using bird song. The technique could offer a way to assess the numbers of hard-to-spot species of bird and could even be used to track the population density of whale and dolphin species.

Deanna Dawson, US Geological Survey, and Murray Efford, University of Otago, New Zealand, recorded the sounds of the Ovenbird, a species of both which is both hard to see and which has a distinctive call, in the Patuxent Research Refuge, near Laurel, Maryland, USA. Using a ‘microphone array’ technique, placing four microphones at intervals and in different locations around the forest, the researchers were able to record the sounds of the ovenbirds and then to combine the recordings from each microphone. Using computer models, the researchers then conducted an analysis, based on the attenuation of the sounds and the relationship between this attenuation and population density, to find the ‘best match’ to the data. In this way they were able to accurately estimate the population size of the ovenbirds.

Biologists have long counted bird songs or calls to generate an index of bird abundance but this relies on being able to see the bird – to assess whether it is within a set distance from the observer. Existing methods of assessing population size also often depend on capturing the birds in nets, which can be very stressful for the animals. This is the first time that sound recordings from a microphone array have been translated into an accurate estimate of bird species populations.

The research has already generated interest from the press in the UK this morning, featuring as a lengthy item on the BBC Radio 4 Today Programme (approx: 7.45am GMT) .
Listen Again to the Today Programme on BBC I-Player

See the Press Release on the BES website: Ecologists sound out new solution for monitoring cryptic species

Deanna K. Dawson and Murray G. Efford (2009). Bird population density estimated from acoustic signals, Journal of Applied Ecology, doi: 10.1111/j.1365-2664.2009.01731.x, is published online today.

New research published today in the British Ecological Society’s Journal of Applied Ecology shows that without international protection the world’s largest species of fruit bat, Pteropus vampyrus or the ‘large flying fox’ could be driven to extinction in Peninsula Malaysia.

A study led by Dr Jonathan Epstein, Wildlife Trust, counted the numbers of P. vampyrus at eight sites in Peninsular Malaysia between 2003 and 2007. The data was compared with the number of hunting licenses issued by the Malaysian Department of Wildlife and National Parks. Based on the average number of licenses issued annually, 22,000 flying foxes per year were allowed to be killed. This rate was unsustainable, even at the most optimistic population estimate of 500,000, as calculated by the researchers’ computer model. At this level of hunting, P. vampyrus will be driven to extinction in between six and 81 years.

By fitting the bats with radio collars, the researchers also revealed that P. vampyrus travels large distances; to Thailand and Indonesia. The bats may travel for up to 60km a night in search of food. Understanding the extent of P. vampyrus’ range will help the co-ordination of international action to protect the bat populations.

Hunting pressure and habitat loss are the two greatest threats faced by P. vampyrus. Commenting on the study, Dr Epstein says: “Our study illustrates that bats, like other migratory species, require comprehensive protection by regional management plans across their range.”

The BES Presidential Address by Sir John Lawton has been published on-line by the Journal of Applied Ecology. Sir John examines how ecology has or has not contributed to policy in a number of areas (fisheries, GM crops). Building upon work in the social sciences, he argues that it is wrong to assume that ‘correct’ policies will result from better scientific understanding by politicians. Ecologists can, and do, influence government policy on the environment, but often via complex and iterative interactions. He suggests the BES could focus on providing scientific advice to politicians and policy-makers and to argue the “ecological corner” through:

• Providing independent, authoritative, in-depth analysis of environmental issues
• Acting as a ‘knowledge broker’ between primary researchers and policy-makers
• Acting as a ‘policy entrepreneur’ by taking novel approaches to difficult problems by working in collaboration with other groups
• Providing a long-term ‘enlightenment function’ by working to change the framework of the debate and seeking ultimately to alter belief systems and deeply entrenched values

The BES’s Journal of Animal Ecology has published a paper that has important implications for the role of badger culling as part of the strategy to control bovine TB in the UK. According to the authors the evidence suggests that movement of individual badgers between groups may be instrumental in driving disease dynamics at the population level, and adds further support to the contention that the social disruption of badger populations, for example by culling, is likely to promote disease spread. Defra recently consulted on whether badgers should be culled to control the spread of bovine TB. A final decision has not yet been announced.