Results

In terms of nest recording, the 2007 breeding season has been incredibly productive. We’ve had another tremendous response from our army of volunteers collecting information for the Nest Record Scheme (NRS – www.bto.org/goto/nrs.htm) and the launch of the Nest Box Challenge in collaboration with the BBC (which you can read about in the next edition of BTO News) has meant that more people than ever are getting involved in monitoring the breeding success of Britain’s birds. It may seem an incredibly simple thing to do, but the value of the information provided by briefly peering into a nest and counting the eggs or chicks inside cannot be underestimated – data such as these hold the key to understanding why bird numbers change from year to year.

While this year has been positive in terms of monitoring effort, feedback received from nest recorders and ringers suggests that it has been less successful for many of the birds themselves, with a general impression that many species, including Great and Blue Tits, had a hard time coping with the incessant downpours during early summer. Large inter-annual fluctuations in breeding success are not the preserve of small passerines, however. In fact, we began last year’s article about the NRS (BTO News 267) by offering our commiserations to the UK’s owl population for what appeared at the time to have been a fairly poor season. Now that the 2006 data have been added to the NRS dataset, which for some species stretches back as far as 1939, it’s clear that productivity was indeed below par for several owl and raptor species. Barn Owl, Tawny Owl and Kestrel, all of which feed primarily on small rodents and particularly Field Voles, produced significantly smaller broods than had been predicted on the basis of long-term trends in productivity. The fact that brood sizes of species such as Common Buzzard, Peregrine, Merlin, Sparrowhawk and Little Owl, which are less reliant on rodent prey, remained unaffected suggests that this drop in productivity was caused by a reduction in vole abundance in 2006.

When looking at such changes in productivity over time, however, it is important to put them into context. Vole populations in the UK are well-studied and it is known that numbers fluctuate regularly on a three-to-five year cycle, variation that is mirrored by changes in the productivity of those bird species feeding on them. Thus, a decline in breeding success in one year may be compensated for by above average productivity the following season and it is only when the average number of offspring produced per pair starts to decline over a longer period of time that conservationists should start to become concerned. Each year, NRS data are used to create trends in productivity for over 90 species, spanning the past 40 years of submitted records, which are available to browse on-line as part of the Breeding Birds in the Wider Countryside Report (www.bto.org/birdtrends). While the most recent trends for Barn Owl and Tawny Owl indicate that productivity has not changed markedly during this period, those produced for Kestrel suggest that brood sizes have declined significantly over the last 15 years (Fig. 1.), leading to the addition of Kestrel to the NRS Concern List.

The NRS Concern List contains those species that are demonstrating simultaneous declines in abundance and at least one aspect of productivity (see Box 1 for details). It is important to exclude species that are increasing in number, as a fall in breeding success may result from heightened competition between individuals rather than from the action of environmental factors that may threaten the conservation status of the species.


The most recent list (Box 2) includes 20 species, two of which, Lapwing and Nightjar, have been added this year due to an increase in egg failure rates and a fall in brood sizes respectively (Fig. 2. and 3.).




Lapwing populations have been in decline since the mid-1980s due primarily to changing agricultural practices, with the loss of the agricultural mosaic, drainage of wetland areas, increased grazing pressure in upland areas and heightened levels of nest predation all implicated in productivity declines. Comparisons of the first and second BTO Breeding Bird Atlases indicate that the range of Nightjar in the UK contracted by more than 50% between the early 1970s and the early 1990s, although the long-term population trend is uncertain.

	Lapwing numbers have been on the wane for over twenty years and an increase in nest failures at the egg stage has occurred over the same period.	John Harding

If you think that reading about the breeding success of different bird species and how it changes over time is fascinating, it really is nothing compared to witnessing it first-hand. While the weather may seem cold and miserable now, it’s amazing how quickly spring begins and the birds start to breed, so when things start to warm up again remember to keep your eyes open for signs of nesting. Records of any species, even Robins and Blackbirds in the garden, are incredibly useful as long as you can see what’s in them, so if you find any please do get in touch with us at nest.records@bto.org and become part of the national army of nest recorders. Thank you None of this research would be possible without the fantastic amount of time and energy that nest recorders invest in collecting these data each year, so thank you very much to everyone who has contributed to the NRS dataset. If you haven’t yet, but would like to in the future, contact us at nest.records@bto.org or look at our web pages at www.bto.org/survey/nest_records/index.htm for more information. Thanks also to Mandy T Andrews for ensuring the NRS runs smoothly, to Karen Wright for all her work on the NRS database, to Mark Cubitt for the design and continued development of the IPMR home-inputting program, which has revolutionised record submission and to David Glue for his contributions to the scheme. The Nest Record Scheme is funded by the BTO/JNCC partnership. Dave Leech, Carl Barimore & Humphrey Crick