British Breeding Population of the Hobby: New Estimate

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.

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