Wednesday, March 24, 2010

Nocturnal visits

Steve White has just sent me some preliminary regional Atlas results for Tawny Owl (see picture). The red dots indicate where we have confirmed recent presence for Tawny Owl - from either breeding or winter data - while the khaki dots indicate records we had from the previous local Atlas in 1997-2000.
Question: Have Tawny Owls really decreased this dramatically over the last 10 years, or is it because we are all afraid of the dark?!
We would like to think it is the latter so, the request is, please try and get out at night in order to collect more data on all nocturnal species - especially owls but also woodcock and, if really lucky, nightjar.
Please do not assume that your observation has already been recorded by someone else. Send everything in - we would rather had masses of (duplicate) data rather than none at all.

Tuesday, March 16, 2010

Swift by name and nature.

Peregrines, as we know, are the fastest thing on two wings being able to reach speeds of 186mph when stooping after prey. However, they are not the fastest bird when flying level this, allegedly, is the spine-tailed swift, with an unconfirmed maximum speed of 105mph in level flight. Now, using verifiable techniques, the record for speed in level flight has passed to the common swift - with a maximum recorded speed of 69.3mph. According to research at Lund University workers have found that swifts do everything 'at the double' whether flying to roost, migrating or feeding, they do it at 22-26mph. But that's not the end of their work - they have found that when swifts come together in 'screaming parties' they will quite often reach speeds of 47mph.
Someone said to me that their year begins with returning Chiffchaff and Willow Warbler, others wait for cuckoo, but this year I'll be waiting for the screaming demons - more particularly as they nest in my roof!

Shrinkage...Bergman's Rule.

According to Bergman's Rule animals tend to become smaller in warmer climates. Historically this has been demonstrated for the same species over latitude or altitude' but a question asked recently was 'given global warming could the same trend be recorded in response to climate change?'
To find out, Dr Josh Van Buskirk of the University of Zurich, Switzerland and colleagues Mr Robert (Bob) Mulvihill and Mr Robert Leberman of the Carnegie Museum of Natural History in Rector, Pennsylvania, US decided to evaluate the sizes of hundreds of thousands of birds that pass through the Carnegie Museum's Powdermill ringing station, also in Pennsylvania.
Examining records from 486,000 birds caught between 1961-2007 they found that of 83 species of spring migrant 60 had become smaller by wing length and weight; and of autumn migrants 66 out of 75 species had reduced in size. Although the time frame appears small we must remember that the birds have gone through at least 20 generations.
It appears then that north American birds are responding to Bergman's Rule however, further analysis is required as changes could be the response to other parameters affected by warmth such as food availability or metabolic rate. Furthermore, it has to be ascertained whether these changes are beneficial or otherwise. For a fuller article see: