A recent article published in Bird Study gives some explanation of the varying numbers of birds you may see on your bird feeder from year to year. Dan Chamberlain, Andrew Gosler and David Glue from the British Trust for Ornithology and the Edward Gray Institute of Field Ornithology, Oxford investigated whether woodland species that feed on beechmast (nuts of Fagus spp.) will have significantly lower occurrence rates at garden feeders in mast years (a year in which there is abundant production of fruit/nuts of trees considered as food for livestock and certain kinds of wildlife*). They monitored garden feeders between 1970 and 2000 for 40 species to assess whether beechmast abundance explained further significant variation additional to underlying seasonal and annual trends.
As you may expect, they found that the 7 species listed below (see end for photos), which commonly feed on beechmast, showed significantly lower occurrence in gardens in years of highest beechmast abundance:
- Great Spotted Woodpecker (Dendrocopos major)
- Woodpigeon (Columba palumbus)
- Great Tit (Parus major)
- Coal Tit (Periparus ater)
- Nuthatch (Sitta europaea)
- Jay (Garrulus glandarius)
- Chaffinch (Fringilla coelebs)
Blackbird (Turdus merula) and Siskin (Carduelis spinus) showed similar significant patterns and are likely to take beechmast as elements of their diet.
So, whether or not your bird feeder is visited by these 9 species this year depends on resources in the surrounding countryside. The authors conclude that food provided in gardens may play a significant part in the population dynamics of these species and consideration of the garden habitat must be factored into population monitoring in future.
Will it be a mast year this year in the UK? According to research conducted by Gianluca Piovesan and Jonathan Adams (2001), probably not. They analysed seed production series from Europe (Fagus sylvatica L.), eastern North America (Fagus grandifolia Ehrh.), and Japan (Fagus crenata Blume), for various periods over the last 150 years and found a close relationship between mast year and preceding growing season climate events in eastern North America and Europe. "A drought in the early summer preceding masting (mast year–1) is a very strong predictor in Europe and eastern North America… The predictive power is increased in all three regions if there has been an unusually moist, cool summer the year before the drought (mast year–2)." As the weather in the UK this summer in no way resembled a hot drought their results would suggest that it is fairly unlikely that you will be missing the above birds from your bird feeder this autumn, but if we have hot, sunny, dry weather early next summer we may be in for a high beechmast next autumn. "We suggest that, in this initial moist summer (mast year–2), carbohydrate buildup within the trees ‘primes’ them for floral induction the following year (year–1). In the European and eastern North American series, a drought event in the early part of the following summer (mast year–1) acts as a proximal trigger for the release of those reserves into flower initiation and then seed production."
Why not invest in a bird feeder this autumn and look out for the above birds – they may be needing the extra food!
Sources (abstracts available to subscribers on CAB Abstracts):
– *Helms, J. A. (ed.) (1998) The Dictionary of Forestry. The Society of American Foresters, Bethesda, Maryland, USA and CAB International, Wallingford, UK, 210 pp. (Available from the CABI Bookshop).
– Chamberlain, D. E.; Gosler, A. G.; Glue, D. E. (2007) Effects of the winter beechmast crop on bird occurrence in British gardens: Capsule Woodland birds were significantly less likely to occur in gardens in years of high beechmast crop. Bird Study 54 (1), 120-126.
– Piovesan, G.; Adams, J. M. (2001) Masting behaviour in beech: linking reproduction and climatic variation. Canadian Journal of Botany 79 (9), 1039–1047.