It has been a long winter, not just for us but also for our mammals, birds and invertebrates. Some indication of just how late winter hung on this year can be seen in the later than usual sightings of spring’s first butterflies or the delayed arrival of our summer migrants (many of which are a fortnight or more behind what we would normally expect).
Perhaps the best indication of the what effects the winter has had on our wildlife comes from the BTO’s weekly Garden BirdWatch survey (www.bto.org/gbw). Each week throughout the year, the 15,000 participants chart the comings and goings in their gardens of birds, mammals, amphibians, butterflies, dragonflies and bumblebees. This community of ‘citizen scientists’ – as the Americans like call them – provides a fascinating insight into patterns of garden use, both between seasons and across years. The latest results from the survey show, for example, that the emergence of hedgehogs from hibernation is nearly a month later this spring that it was in either 2011 or 2012. Even the cold start to 2010 only saw hedgehog emergence delayed by a fortnight.
Of course it is not just a case of the hedgehogs emerging just a little bit late. A late emergence means more time spent in hibernation, placing greater strain on the energy reserves that were laid down last autumn. It seems likely that there will have been higher levels of overwinter mortality this year, something that may place additional strain on a population that is known to be in decline. It is not known just how many of our hedgehogs die during hibernation but mortality levels among young animals, born the previous summer, is thought to be high. A study in southern Sweden, where winter conditions are more challenging, found that just under a third of young hedgehogs entering hibernation failed to survive through to spring.
Newly emerged hedgehogs will need to feed up, replacing lost resources, before the breeding season starts in late April or early May, with the first young normally born in the last week of May. This year, however, I suspect that births will be delayed, shortening the amount of time that newly independent youngsters will have to fatten themselves up ahead of entering hibernation, something that can begin as early as mid-October. The first individuals to enter hibernation are the adults and youngster may remain active for longer, suggesting that they are still seeking out feeding opportunities and trying to achieve a body weight that will see them through the winter. Let’s hope that the summer is long and delivers good numbers of large invertebrates on which this year’s generation of hedgehogs can fatten themselves up.