Wednesday, 31 May 2006

Scheme charts nesting success

On a Saturday, by accident, I found my first yellowhammer nest of the year, situated just above the ground in a hawthorn bush and surrounded by rank grass. The presence of the nest was revealed when a female yellowhammer shot out of the bush I had just tapped with my butterfly net. Tapping bushes is a useful way of discovering hidden butterflies and other insects.

The nest was made of grass stems, woven together and lined with fine grass and hair. The front edge sported a ‘doorstep’, often characteristic of the species, and inside were three off-white eggs. Each egg was beautifully marked with a mixture of thin and thick squiggles, almost as if some child had taken a fine pen to a blank egg and added a random design. Having counted the number of eggs and checked that they were warm, I moved away to let the female back on. From a distance, I made a mental note of where the nest was located and jotted down a few notes in my field notebook. This would enable me to make further visits to the nest over the coming weeks and to collect information of value to the British Trust for Ornithology’s (BTO) Nest Record Scheme. Through the scheme, the BTO is able to gather essential information on breeding success and productivity for a large number of our breeding species. This information is then used alongside that from other BTO surveys to help find out why particular species are in decline or on the increase. The network of Nest Recorders operates under a strict code of conduct. This governs the way in which nests are visited and standardises the way in which information is collected. Recorders typically make a number of visits to each nest throughout the nesting period, in order to collect information on the number of eggs laid, the number which hatch and the number of chicks which survive through to fledging. Perhaps the most important information concerns the outcome of the nesting attempt: was it successful or did the nest fail because of predation, weather or desertion?

The timing of my visit, coupled with the presence of an incubating female, suggested that the clutch was complete at three eggs (yellowhammers may lay up to five eggs but don’t start incubating until the final egg has been laid). This will enable me to plan the timing of my next visit so that I can collect information on hatching success and gain a better indication of when the first egg had been laid. Two more visits will follow this and then I will send in my completed Nest Record Card to the BTO to add this important dataset.

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