Reflections on a poor nesting season

Looking back at summer 2012, it is easy to see why the preliminary results emerging from the British Trust for Ornithology’s Nest Record Scheme (www.bto.org/nrs) highlight a poor nesting season for many bird species. Interestingly, 2012 got off to a good start, with February and March both warmer and drier than average. This prompted early-nesting species like tawny owl, song thrush and long-tailed tit to initiate nesting attempts far earlier than the five-year average. Song thrush was, on average, starting a week earlier than usual and tawny owl a fortnight earlier.

In contrast, newly-arriving migrants returning from their African wintering areas just a few weeks later were faced with some awful weather, not just here in Britain but also further south in Europe. The consequence of this was a delay in arrival dates for many species, with courtship, nest construction and egg-laying also delayed. Whitethroats were 15 days later than usual in starting, reed warblers 11 days and Swallows 7 days.

As the cold and wet weather continued there were problems for resident breeders as well. Blue tits and Great Tits, which depend on caterpillars for their growing young, faced particularly challenging times. In both of these species clutch and brood sizes were down and the number of young fledged was significantly reduced. Again the BTO figures suggest that the number of blue tit fledglings produced was down by 13% on the five-year average, the comparable figure in great tit being nearly 18% down. Looking longer-term, the preliminary results suggest that, for great tit, 2012 saw the lowest number of chicks fledged per breeding attempt since the scheme began in 1966. For many of the volunteers involved in monitoring nests this was the worst year they had encountered. Some, notably those working on waterbirds, waders and reed warblers, faced large losses as widespread flooding washed out vulnerable nests. It was a season to forget, but nonetheless important for charting the impact of what might become a more common weather pattern in the face of a changing climate.

What happens longer term will depend on what happens over the winter. With fewer young recruited into the population there should be less competition for winter food and we might see a prompt recovery if we have a good breeding season in 2013. Many of these species are facing other pressures, however, and so things might not be as simple as they first appear. What is clear though, is that the efforts of volunteers who give up their spare time to count and monitor birds are central to our understanding. Without their passion and enthusiasm, we simply would not know about the effects of a changing climate on our birds and other wildlife.