Garden birds indicate widespread failure in seed crops
01 Feb 2013 | No. 2013-10
Annual results from the weekly BTO Garden BirdWatch, which have just been published, reveal a significant movement of Jay, Nuthatch and Coal Tit into gardens during Autumn 2012, suggestive of a widespread failure in the seed crops of various trees. The results also reveal a substantial change to the seasonal pattern of garden use by Siskin, a species of finch that has benefited from maturing conifer plantations more widely. Earlier in the year, there was also a substantial cold weather movement of thrushes into gardens when a period of widespread snowfall made feeding conditions elsewhere difficult.
Some 15,000 ‘Citizen Scientists’ support the BTO’s Garden BirdWatch survey, submitting observations of the birds and other wildlife using their gardens on a weekly basis throughout the year. These observations are analysed and interpreted in real time as they come in to the BTO’s database of 86 million observations. Looking back at the previous 12 months, however, provides an opportunity to pull together the main patterns and stories and to examine these alongside other sources of information.
The biggest story was the very large influx of Jays, Nuthatches and Coal Tits to UK gardens during late summer and early autumn, strongly suggestive of a widespread failure of the tree seed crops on which these species depend. By the end of September, the numbers of Nuthatches using UK gardens were up by 91% on the long-term average, while Jays were up by 70% and Great Spotted Woodpeckers were up by 64%. The poor crop of beechmast is thought to be behind such a pronounced movement into gardens, with effects also seen in Woodpigeon, Great Tit and Chaffinch. A similar pattern was seen in some of the species feeding on conifer seed, notably Coal Tit and Siskin1.
2012 was an exceptional year for Siskins in gardens. The normal pattern of garden use in this species has tended to be for a late winter peak (in January and February), numbers then remaining low through spring and summer and only increasing again from late November. The late winter peak was much reduced in 2012 but was then followed by three other peaks: one in late April (linked to a period of poor weather), one in late June (linked to family parties looking for food) and one in September (matching the poor autumn seed crop). Use of gardens throughout the summer months and early autumn is increasing in this species, to the extent that one in ten gardens is now visited by Siskins during a typical summer week. This reflects an increasing breeding population, supported by maturing conifer plantations, and increased use of garden bird feeders.
A pronounced movement into gardens during early February 2012 was noted for a number of bird species, including Blackbird, Fieldfare, Redwing, Song Thrush, Black-headed Gull and Reed Bunting, underlining the important role that garden feeding stations play during periods of cold weather and snow cover.
Mike Toms, Head of Garden Ecology at the BTO, commented "The weekly Garden BirdWatch survey is proving to be a very powerful tool, enabling us to monitor the changing use of gardens, bird tables and hanging feeders by birds. To be able to pick up the effects of failing seed supplies, periods of cold weather and changing breeding populations is key to understanding the role that gardens play within the wider landscape. It is only because of the efforts of our ‘citizen scientists’ that we are able to collect and use this important information on a weekly basis throughout the year."
Notes for Editors
- McKenzie, A.J., Petty, S.J., Toms, M.P. & Furness, R.W. (2007) Importance of Sitka Spruce Picea sitchensis seed and garden bird-feeders for Siskins Carduelis spinus and Coal Tits Periparus ater. Bird Study 54: 236-247. To see report please visit here
- This figure (Fig. 1) shows how the numbers of five different (tree seed-eating) species changed through autumn 2012 in relation to the long-term average. It demonstrates the exceptional movement of Jay, Great Spotted Woodpecker and Nuthatch into gardens.
- The pronounced increase in Nuthatch numbers is clearly evident when compared to previous years (Fig. 2).
- The BTO Garden BirdWatch is the only nationwide survey of garden birds to run weekly throughout the year, providing important information on how birds use gardens, and how this use changes over time. Currently, some 15,000 people take part in the project. The project is funded by participants’ contributions and is the largest year-round survey of garden birds in the world. For more information see www.bto.org/gbw.
- 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
(BTO Head of Garden Ecology)
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Email: mike.toms [at] bto.org
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