NRS Preliminary Results 2011

Since 1939, the Nest Record Scheme (NRS) has been collecting information on the timing of breeding and the productivity of nesting attempts in the UK. Each spring and summer, over 500 volunteer nest recorders follow the progress of more than 30,000 nests of a huge range of bird species that they find in their gardens or in the wider countryside. The information that they collect allows us to understand how the number of young that each species produces has changed over time and to determine whether this has caused a significant change in the size of the population.

NRS preliminary results for 2011

Trends in breeding success over the last four decades are published each year in the BirdTrends Report , but it currently takes almost 12 months to collate and analyse all the information. Last year, we asked recorders to submit their data as early as possible, which allowed us to produce the first ever set of preliminary results for the seven most commonly recorded species. The response to a similar request following the 2011 season has been even more positive, with 22,000 records already received by the end of October, an increase of over 50% relative to 2010. As a result, we have been able to produce preliminary results for a total of 18 species (Table 1), comparing productivity during the 2011 season with the average over the preceding five years (2006-2010).

Species

Clutch

size

Brood

size

Egg stage
survival
Chick stage
survival
Fledglings
produced
Kestrel 0.0 6.8 2.4 3.1 14.6
Barn Owl 7.2 3.9 1.6 1.3 1.3
Tawny Owl 1.6 6.0 -7.8 1.2 -2.1
Swallow -1.0 -0.3 -0.4 2.1 0.6
Dunnock 0.7 -0.4 -0.6 19.0 19.7
Robin 1.4 4.9 11.6 -15.9 -1.3
Blackbird -0.9 -1.0 -1.8 3.2 -0.1
Song Thrush -2.2 -0.2 11.9 4.5 13.4
Reed Warbler 1.1 2.9 0.9 -1.0 3.0
Blackcap 0.5 4.5 -15.1 -7.0 -15.6
Whitethroat -5.8 -5.8 3.8 -7.4 -12.0
Chiffchaff -1.0 -2.9 -0.9 2.3 2.5
Willow Warbler -3.0 1.5 -9.3 1.4 -8.0
Pied Flycatcher 2.4 1.6 1.4 -2.4 0.9
Blue Tit -3.6 2.8 1.1 4.0 3.4
Great Tit 6.4 10.0 1.5 1.8 12.2
Tree Sparrow -0.1 3.8 -4.3 -4.1 -6.1
House Sparrow 0.9 -1.2 0.2 1.0 5.1

Table 1. Percentage change in breeding success in 2011 relative to the average for the previous five
years. Significant increases are in green; significant decreases in red.

Woodland box-nesting passerines like Great Tit (top), and small-mammal-eating Raptors like Kestrel (bottom), had good breeding seasons in 2011.

Rodent specialists produce bumper broods

In contrast to the 2010 season, during which Barn Owl brood sizes fell to one of the lowest levels on record, 2011 appeared to be a very productive year both for all three of the small mammal specialists included in these analyses; Barn Owl, Tawny Owl and Kestrel. Anecdotal reports of well-stocked prey larders suggest that rodents were plentiful during the breeding season, and the warm, dry spring weather provided perfect hunting conditions. Kestrel appeared to fare particularly well (Figure 1), exhibiting a 15% increase in the number of fledglings produced per nest, welcome news for a species whose recent population decline , particularly in England, has raised concerns amongst conservationists.

Great year for Great Tits

Fig 1. Both Kestrel (top) and Great Tit (bottom) produced a
significantly higher number of fledglings per breeding attempt
in 2011 relative to the previous five years.

The NRS results from 2010 indicated that it had been a very good year for woodland box nesters, with Blue Tit, Great Tit and Pied Flycatcher all producing large numbers of fledglings. This positive trend continued into 2011 thanks to the warmest, and one of the driest, spring since the mid-1960s, with Great Tit faring particularly well, producing the highest number of fledglings per nest since 2002 (Figure 1). The same could not be said of the two other cavity nesters, House Sparrow and Tree Sparrow; while brood sizes of the latter were significantly higher, a greater proportion of nests failed during incubation, and the number of fledglings produced by both species was close to the average.

A middling season for open nesters

Many of the additional species for which preliminary trends were produced in 2011 were open nesting passerines, including a good mix of residents (Song Thrush, Robin, Dunnock), short-distance migrants (Blackcap, Chiffchaff) and long-distance migrants (Reed Warbler, Whitethroat, Willow Warbler). There was some suggestion that migrant breeding success was lower than in recent years, particularly for Sylvia warblers, with Whitethroat clutch and brood sizes both significantly reduced. However, the number of offspring fledged did not differ significantly from that recorded during the previous five years for any migrant species. Residents appeared to fare better overall, with Song Thrush and Dunnock productivity particularly high, although again these differences were not statistically significant.

Help us produce NRS results in 2012!

All of the data used in these analyses are submitted by volunteers, so if you’re not already a nest recorder, why not consider becoming one? We’re interested in receiving records of all nests anywhere in the UK as long as you can count the contents accurately – even the Blackbird in your garden is sitting on valuable data! nrs [at] bto.org (Email us) for your free Quickstart Guide or visit the NRS web pages to find out more about taking part in this vital survey.

Acknowledgements

We’re extremely grateful to all those nest recorders taking part in the NRS, both for collecting the data and making the additional effort to submit it quickly, and for the support given under the JNCC/BTO partnership that the JNCC undertakes on behalf of the Country Agencies.