Is avian breeding success weathering the storms? Latest results from the Nest Record Scheme

Dave Leech and Carl Barimore report on the latest Nest Record Scheme productivity trends and find out how the birds fared during a 2007 breeding season that was characterised by unseasonably heavy rain and flooding.

For the second year in a row we appear to have come to the end of a summer that never really felt like it had started in the first place, characterised once more by heavy rain and strong winds. For many Nest Record Scheme (NRS) participants, weather such as this evokes much the same feelings as those experienced by parents whose children have gone to school/summer camp/university for the first time. After all the love and attention invested in finding the nest and following the breeding attempt, every shower brings new fears of catastrophe and premonitions of disaster. We feel compelled to keep checking that the offspring are OK and to interfere if we suspect that things may be about to take a turn for the worse, but we must restrain ourselves and let them fend for themselves. The poor weather in 2007 certainly didn’t dampen the enthusiasm of nest recorders, however, and an amazing effort by all concerned saw submissions top the 35,000 mark for the first time since 1999.

It never rains ......

….but it certainly poured in 2007, with several months achieving the unwelcome status of ‘wettest since records began’. In terms of productivity, the most successful group of species were those predating small mammals, the three-five year population cycle of rodents in the UK having hit a peak in 2007. Brood sizes of Tawny Owl, Barn Owl and Kestrel were 8%, 18% and 14% larger respectively than predicted from long-term trends. Little Owl and Starling were also more successful than might be predicted, both possibly having benefited from increased accessibility to soil invertebrates in which they primarily feed in the wet weather conditions. Nuthatch also demonstrated above average breeding success – researchers in Europe have previously identified a counter-intuitive positive correlation between the breeding success of this species and spring rainfall, although the reason for this relationship remains unclear.

	The abundance of rodents in 2007 resulted in above average Barn Owl clutch and brood sizes.		Jez Blackburn

In contrast, many resident open-nesting species showed levels of productivity that were lower than predictions made using data from previous years. Resident open-nesters, particularly Robin, Dunnock and Wren, appeared to be particularly badly affected, exhibiting reduced clutch and brood sizes and increased failure rates, as did Reed Warbler. It is interesting to note that ringers participating in the Constant Effort Scheme (CES, www.bto.org/goto/cesnews.htm) also reported lower proportions of juveniles of these species in their catches in 2007. CES and NRS results were not in agreement across the board, however, nest recorders finding little evidence for the reduction in productivity of Blue Tit and Great Tit apparent from the CES dataset. This discrepancy suggests that weather conditions may also have influenced post-fledging survival and illustrates the importance of combining a range of techniques when investigating trends in avian demography.

	Resident open nesters such as Robin had a relatively poor year in 2007, producing smaller clutches and experiencing increased rates of nesting failure.		Jill Pakenham

The importance of being trend-y

While the annual fluctuations in breeding success provide a fascinating insight into the processes that determine the number of offspring that birds are able to produce, it is the long term trends in productivity that are of greatest use to conservationists. The NRS Concern List highlights those species that have demonstrated recent declines in both abundance and some aspect of productivity (see Box 1 for more details). While no new species have been added as a result of the latest analyses, a recent increase in mean brood sizes has lead to the removal of Starling, leaving a revised total of 19 (Box 2). The species of greatest concern are Yellowhammer and Spotted Flycatcher, which currently exhibit statistically significant declines in all four breeding parameters derived from the NRS dataset (clutch size, brood size, egg survival rates and nestling survival rates). The trends for Linnet, Bullfinch and Nightjar are also worrying, with three of the four breeding parameters calculated for each species indicating a significant reduction in productivity. Equivalent trends are calculated for over 90 species and published on-line each year in the breeding birds in the Wider Countryside Report – take a look at the latest results at www.bto.org/birdtrends.

	Mean Spotted Flycatcher brood sizes have been falling since the mid 1980s, during which period the population has continued to decline. Graphs such as this one are produced and updated for over 90 species each year and can be found on-line at www.bto.org/birdtrends.

Looking to the future

It simply wouldn’t be possible for us to produce this article, or indeed the majority of the articles in this magazine, without the amazing contribution of our dedicated volunteers. There are currently over 500 nest recorders in the UK, but there is always plenty of room for more, so please email nest.records@bto.org if you’d like to join in. We are also extremely grateful for the support given under the JNCC/BTO partnership that the JNCC undertakes on behalf of English Nature, Scottish Natural Heritage, Countryside Council for Wales and the Environment and Heritage Service in Northern Ireland. As reported previously, the incredible generosity of Dilys Breese has enabled us to embark on an ambitious development plan for the NRS which you can read all about in the next issue of BTO News, so watch this space!