Birds count cost of awful summer

It has been a poor summer for many of our breeding birds. The appalling weather that dominated from May through into July caused problems for nesting bitterns and lapwings, both caught out by rising water levels, and made life very difficult for nesting tits. It had all started so well, with the fine weather in April favouring early nesting species, like the long-tailed tits which had a bumper season. However, those birds nesting later in the year were caught out.

Species like blue tit and great tit time their nesting attempts to coincide with the annual peak in the abundance of caterpillars. They need to do this because each chick (and there may be up to 12 in a nest) requires something like 100 caterpillars per day. The arrival of heavy rain literally washed many caterpillars off the leaves, making food more difficult to locate for busy parents. Short on food, the growing chicks were also hampered by the fact that their parents were returning to the box wet. With far fewer body feathers than their parents, chicks quickly became damp and chilled and many a brood was reported dead in the nest.

Information from those with nest boxes in their garden made it apparent fairly early on that it was not going to be a good breeding season. These anecdotal reports have now been supported by the recently published results of systematic monitoring work carried out by the British Trust for Ornithology (BTO). Through the Constant Effort Scheme (CES), bird ringers working for the BTO collect vital information on movements, survival rates and productivity. Every summer, teams of CES ringers catch birds by using a system of special nets, with each net used in the same place and for the same length of time from one year to the next. This enables the researchers to look at the numbers of adult and juvenile birds that have been caught and, from this, establish a measure of breeding success. The 2007 breeding season has proved to be the worst on record for a number of species: blue tit productivity was down by half, that for great tit was down by a third and two migrant species (reed warbler and whitethroat) were down by a quarter. While a good breeding season next year may enable some birds to bounce back quite quickly, for others the poor summer is yet another thing that has gone against them. Some of the migrant species, like whitethroat, are facing problems on their wintering grounds in Africa and a poor breeding season here only serves to exacerbate their plight. We need to keep our fingers’ crossed for a better breeding season in 2008.