Providing extra food in early spring led to earlier egg laying and increased productivity for the Great Spotted Woodpecker.
Birdwatchers have been amazed by the big increase in the numbers for Great Spotted Woodpeckers over the last 15 or so years. In a paper in the latest issue of Bird Study, the journal of the British Trust for Ornithology, authors Ken and Linda Smith provide a potential explanation for the woodpeckers’ success.
In a wood in Hertfordshire, Great Spotted Woodpeckers were provided with suet blocks at 13 feeding stations distributed over half of a 100-ha study wood from early February until late April 2011, with the other half of the wood left unfed. In the spring of 2011 breeding attempts in the 'fed' zone were earlier, by an average of four or five days and birds there produced almost twice as many fledged youngsters as those in the unfed zone, even though the supplementary feeding stopped before the main period of chick rearing.
BTO Members, Ken and Linda Smith had been studying the woodland for the previous five years and found no differences between the zones in any of the previous years when no extra food was provided. The availability of caterpillars, the natural food for the breeding woodpeckers, was measured by using 'frass' traps to collect their droppings. 2011 was a very warm spring and the natural prey abundance peaked very early. This meant that none of the woodpeckers' breeding attempts were well synchronized with the emergence of the caterpillars. However, the small advancement in first egg date meant the supplemented birds were better synchronized than the birds that did not have access to suet blocks. Birds in the fed areas raised an average of 4.2 chicks per pair, compared to 2.1 chicks per pair in the unfed areas.
Ken Smith said "Having studied these birds for best part of 30 years, I was amazed at the difference extra food made in 2011. A few days' shift in egg laying date allowed them to be so much more productive."
The response of Great Spotted Woodpeckers to supplementary feeding suggests that they may be limited in their ability to shift their breeding period in response to the earlier boom in caterpillar numbers. This has important implications for the response of the birds to warm springs, which are expected to be more frequent under future climate change. By using feeders, Great Spotted Woodpeckers breeding in woodlands close to gardens may well be able to avoid problems caused by the changing timing of the spring season. By producing a big brood of youngsters, even in early springs, garden-feeding parents may be helping to fuel the current population increase.
Notes for Editors
- English Great Spotted Woodpecker numbers rose by 122% in the period 1995 to 2010, according to Breeding Bird Survey data. BBS is jointly funded by BTO, JNCC and the RSPB.
- The study was carried out in Wormley Wood, Hertfordshire, a mature Oak and Hornbeam wood and a long-term study site for Great Spotted Woodpeckers. The wood was selected because of its large extent (100 ha), relatively uniform habitat, good numbers of breeding woodpeckers (around 25 pairs in recent years), and its relative isolation from houses and gardens, where supplementary feeding may have already been taking place.
- The BTO is the UK's leading bird research charity. A growing membership and up to 60,000 volunteer birdwatchers contribute to the BTO's surveys, collecting information that underpins conservation action in the UK. The BTO maintains a staff of 100 at its offices in Thetford, Stirling, Bangor (Wales) and Bangor (Northern Ireland), who analyse and publicise the results of surveys and projects. The BTO's work is funded by BTO supporters, government, trusts, industry and conservation organisations. www.bto.org
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