It is not so much the rain of June and early July that has caused the problems for our reed warbler project but the wind. The seemingly relentless run of windy days that hit during the second half of June tipped the contents from nests as the reeds bent and shifted. Weekly visits to the reed bed revealed an all too familiar picture; nests that had eggs or young chicks were now empty or gone altogether.
Reed warblers are, however, robust birds and quick to replace a nest with eggs that has been lost. In fact, some of the nests that disappear (leaving behind the tiny marker tape placed beneath the nest) are dismantled by the birds themselves, the material reused for the new nest placed just a few feet away. It was during our first field season that we first noticed this tendency to dismantle a failed nest and on occasion it caught us out. During that first season we only marked the location of a nest with a piece of tape placed on the track that we used to move through the beds. The nest itself would be unmarked but located within a few feet and easy enough to spot. Sometimes, however, you would arrive at the tape, recall the location of the nest and then adopt a puzzled expression at either your failure to refind it or to find that it had moved by a few feet. The addition of that second piece of tape leaves no doubt that a nest has been dismantled and moved.
Those nests placed in the most sheltered parts of the reed beds seem to have done alright, the birds rearing their young to fledging before probably making a second breeding attempt. Others may have lost their clutch to a cuckoo, the cuckoo chick typically hatching first and quickly jettisoning its hosts’ eggs over the side of the nest. The cuckoo chicks have not had it all their own way though, the windy conditions have taken their toll on them as well. So far, just one of the cuckoo chicks has fledged, others have only just hatched and others were lost to the weather.
Working so closely alongside these birds generates a degree of affection and you feel for the reed warbler pair in whose nest you spot a cuckoo egg. You know that this breeding attempt will be a failure for the warblers but the sadness is countered by the hope that a young cuckoo will fledge. After all, it is the cuckoo that is in decline while the reed warbler remains one of the few African migrants that seems to be flourishing. Lets hope the weather gives them both a fair crack over what is left of the season.