Thursday, 6 May 2010

Semi-colonial finches

It’s been a tough day and I’m still picking the bits of dead gorse out of my clothes, shoes and skin. It has been worth it though, a day spent looking for nests so that we can monitor them over the coming weeks and feed our observations into an important national scheme. The effort has been targeted at the BTO’s Nunnery Lakes reserve, which lies to the south of Thetford and runs parallel to the Bury Road. The diversity of different habitats on the reserve means that it supports a wealth of different bird species, many of which also nest here. Much of today’s effort, however, has been aimed at the gorse which dominates the ridge above the old gravel workings. It is here, within these dense and spiny bushes, that the Linnets choose to nest.

Linnet nest, by Mike Toms

Linnets are semi-colonial breeders, which means that several pairs will nest in close proximity, often in neighbouring bushes. Rather than actively searching each bush in turn, we seek to target our efforts most effectively by first watching the bushes and the Linnets to see if we can narrow down where we need to search. Having so many pairs in close proximity complicates things and it requires a good period of patient watching in order to pinpoint the nests from afar. The males like to use prominent perches, many of which will be a little way away from the location of the nest. Sometimes, however, the male will call the female from the nest and the two birds will leave the reserve to feed on the set-aside land on the neighbouring estate. Watching their subsequent return can be particularly helpful.

There are times when unexpected events can help to reveal the location of a nest. One of the males had been perched on a bush for some time but then moved off. Just after he had left, a Great Tit appeared and proceeded to forage near where the male had been sitting. Just then, a female emerged from the bush to chase the Great Tit away. Satisfied that she had done her job the female Linnet entered the bush again, just a few feet from where she had first emerged. Somewhere in between those two points would be her nest. Needless to say, we found it straight away when we went to check the bush.

Subsequent visits to these nests, made briefly some seven to 10 days apart, will enable us to record the fortunes of each nesting attempt. They will reveal the number of eggs and chicks and how many young fledged successfully. In turn this will enable the BTO’s researchers to establish how Linnets are doing, providing conservation advice that will help us look after this, and other, species.

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