British Breeding Population of the
Hobby: New Estimate
Reference: Clements, R, The Hobby in Britain: a New
Population Estimate, British Birds 94(9) 402-408. (2001).
Notes from the paper:
During the past 20
years this falcon has spread north and west from its original
stronghold in central southern England.
Figures suggest that
the British breeding population may be as high as 2,200 pairs.
In well-studied Kent,
the minimum density is 3.3-3.9 pairs per hectad (10-km square). The
county population is 120-140 pairs.
To the north, it is
now breeding regularly in Northumberland (N. Rossiter in litt), it
has recently bred in Scotland, and it is present in fair numbers in
parts of Derbyshire, Cheshire and Yorkshire (p.405).
The calculated
estimate for the British population is 2,264 pairs but this really
refers to successful attempts only.
In Germany 22.5%
failed so the actual population may be over 2,500 pairs.
Productivity, from
BTO nest record cards, is rising from 1.96 young/successful pair in
1970-79 through 2.05 1980-89 to 2.44 in 1990-99.
The estimate is based
on three pairs per hectad in 'good' habitat and one pair per hectad
in less good habitat (mainly arable).
It does not breed above 300m asl so in upland
areas it is restricted to linear populations on farmland along river
valleys.
Comments:
The Hobby has many similarities to the Honey
Buzzard:
It
feeds to a substantial extent on insects (in the Hobby's case, eaten
directly or as birds which eat insects).
It
is consequently a summer visitor.
Therefore no winter work is possible to locate
territories outside the breeding season.
It
is very secretive in its breeding areas.
Some
observers are also very secretive in reporting sites that they find.
Much
of its habitat can be quite ordinary countryside, rarely visited by
birdwatchers.
Its
identification also presents some problems to observers not familiar
with the species in its breeding areas.
There are some clear differences:
The
Honey Buzzard also eats frogs and young pigeons Subsequent
Trends , enabling it to breed further north
than the Hobby.
The
Honey Buzzard is less likely to cross the open sea (as a
broad-winged raptor) than the Hobby (as a falcon).
Hobbies
do not consequently concentrate at narrow sea crossings. For example
they are apparently scarce in the Straits of Gibraltar.
As
a broad-winged raptor, rather than a small falcon, the Honey Buzzard
is more likely to be persecuted than the Hobby.
The conclusions are obvious:
Recent
population counts for the Hobby, e.g. Rare Breeding Birds Panel for
1999 of 246-553 pairs Report
of Panel , are clearly serious
underestimates by a factor of around five (dividing 2,500 by 553).
The
final results for the count of Honey Buzzard sites in 2000 of 69
Results
also needs to be adjusted upwards by a substantial
amount. Using the figure of five for the Hobby gives a population
estimate of around 350 pairs for the Honey Buzzard in Britain in
2000.
The
breeding range of the Honey Buzzard is likely to be wider than that
of the Hobby in Britain because of its lower dependency on insects.
Until
the recent reduction of persecution from the early 1990s onwards,
the population of the Honey Buzzard will have been kept at a
substantially lower level than that permitted by the habitat.
Over
a long period, Honey Buzzard populations can be gauged from passage
at migration points while those of the Hobby cannot.
