Wednesday, 28 December 2011

Preliminary results from the BTO 2011







The preliminary results from the British Trust for Ornithology’s 2011 Nest Record Scheme (to which we contribute by submitting all of our breeding records) indicate a happier 2011 for the nation’s Barn Owls following the disappointments of the previous year.

Nationally Barn Owls had a disappointing season in 2010, with mean brood sizes falling to their lowest level for a decade. The extremely cold winter of 2009/10 may have left females in poor condition at the start of the breeding season, reducing the amount of energy available to invest in egg production, leading to below average clutch sizes. The harsh winter weather conditions may also have affected vole numbers later in the season, although snow cover can actually be beneficial to small mammals as it shields them from predators.


Barn Owl chicks. Photo by Colin Shawyer
 Barn Owl brood sizes in 2010 (red dot) were the second lowest since 1985

Percentage breeding success in 2011 relative to the average for the previous five years. Significant increase in green; significant decreases in red.

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




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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 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, 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.
 
 Small-mammal-eating Raptors, like the Kestrel, had good breeding seasons in 2011.


Locally in Mid-Cheshire we did not enjoy the same success in terms of brood size and fledging success as that which is depicted nationally; although we did find 41 successful breeding Barn Owl pairs which managed to fledge 110 young.