Tuesday, 21 June 2011

Strong winds cause problems

The combination of chest waders and lifejacket is not the most flattering of outdoor looks but it has become my regular attire this summer. Once or twice a week I am out monitoring a reedbed population of Reed Warblers as part of what we hope will become an important long-term study. Thanks to the generosity of the landowner we are able to monitor the nesting behaviour and breeding success of a sizeable Reed Warbler population using a series of old gravel workings.

While many of our long-distance migrants are undergoing substantial declines, the Reed Warbler is currently showing an increase in abundance and so it has received rather less attention than is, perhaps, desirable. The Reed Warbler is an important host for the Cuckoo, a species which is in decline, and it is important for us to learn more about Reed Warbler populations and the extent to which Cuckoos use them. So far, this season has not been that good for the Cuckoos parasitizing our reedbed warblers. Some of the reedbeds on the site are rather exposed and the strong winds of late May resulted in many nests losing their contents, as the reed stems to which the nests were attached bent over in the wind. This resulted in the loss of some Cuckoo eggs and chicks. The Reed Warblers will try again though, as will the Cuckoos over the short time they remain in the country.

One aspect of our work that is of particular interest is the pattern of breeding attempts. Some authors suggest that Reed Warblers have three broods in a season, while others think that the three broods are actually three waves of breeding: the first and last being attempts by older birds (in effect first and second broods), while the second wave is made up of young birds (in their first year of life) who return to the breeding grounds somewhat later in the summer. To test this, we are attempting to fit rings to all of the chicks reared on the site to see if and when we recapture them in future years. In order to be systematic about the recapturing component of our work, we operate a series of nets in set positions, once every ten days.

Monitoring the nests also provides information on breeding success. Last year, for example, the number of eggs laid (3.67 per nest) was lower than the national average but the survival of the nests through to fledging was higher, so that the number of fledglings produced per breeding attempt was similar to that at other UK sites. Large-scale, long-term studies are uncommon, which makes our work particularly important. It is going to be fascinating to see what we discover over the coming years.

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