Worcestershire Record No. 6 April 1999 p. 16

COMMON BUZZARDS IN WORCESTERSHIRE

Introduction

Against that background the current situation in West Midlands had improved by the late 1990's to such an extent that they are commonly seen throughout much of Worcestershire, Staffordshire, and even Warwickshire. It was decided to conduct a survey during 1997 and 1998 to try to discover the current distribution of the Common Buzzard in Worcestershire.

This paper aims to show the results of the fieldwork, and to discuss the possible reasons for the turnaround in the species' fortunes. 

History

The first proper survey of an increasing Common Buzzard population came in 1954. This revealed 13 breeding pairs in the county, plus single pairs in Staffordshire and Warwickshire. The Worcestershire birds were largely confined to the west of the county, and particularly the Teme Valley. The date of the survey proved significant as it just pre-dated a serious outbreak of myxomatosis which decimated the Rabbit population. The situation was worsened by the effects of organochlorine poisoning which were prevalent at the time. The result was a drop in the Common Buzzard population to no more than four pairs by 1958.

Between 1966 and 1968 the WMBC Atlas project revealed just one 10km square containing breeding Common Buzzards, although by 1972 fieldwork for the national Atlas project had doubled that.

There was a clear improvement by the second national Atlas, 1988 to 1991 with as many as 10 10km squares containing breeding Common Buzzards. It seems likely that the situation had already improved beyond the 1954 position.

An interesting comparison can be made between the figures for the number of breeding season reports of Buzzards reported to the county recorder in Worcestershire from 1984 to 1986 compared to those reported from 1994 to 1996.

Table 1. Breeding season reports in Worcestershire reported to WMBC in the 1980s and 1990s

The usual tetrad, 2km national grid square was taken as the mapping unit, and observers were encouraged to record all Common Buzzard sightings from mid-March to the end of August within the area they were covering.

Within each tetrad, the status of Common Buzzards was given a code A, B, C, or D. The following definitions were applied:

It was apparent from the results that the primary method used by observers to establish proof of breeding was the observation of recently fledged family parties containing food-begging youngsters. This is not surprising given the secretive nature of the species in the season, and it does give some cause for concern because of the possibility that the observation was made in a tetrad neighbouring the one in which breeding actually took place. On the other hand it seems likely that a number of breeding attempts may have taken place in squares where simple territorial activity was noted.

Taking the figures for confirmed and probable breeding as the most significant, the total breeding population for the county would appear to be between 59 and 121 pairs. Interestingly however, it has been suggested that the number of soaring birds correlates well to the number of Common Buzzard pairs actually breeding. If this is the case, then the number of tetrads containing Buzzards simply in potential breeding habitat becomes more significant, and could raise the upper figure to 175 pairs.

Figure 1. The distribution of Common Buzzards in Worcestershire in 1997 and 1998

The above data show that Common Buzzards breed or probably breed in all but three 10 km squares containing at least five tetrads. Confirmed or probable breeding taking place in 91 tetrads to the west of the SO 900 line of longitude and 30 tetrads to the east of it. 

Discussion

Looking at persecution levels presents an immediate problem. Common Buzzards have been a protected species along with almost all other birds of prey since 1954. Subsequent legislation has been implemented mainly through the Wildlife & Countryside Act 1981, which made it an offence to intentionally kill, injure or take, or to attempt to kill injure or take, any wild bird, nest, or egg. The Common Buzzard does not, however, qualify for Schedule 1 of the Act which would have given them even more protection.

Incidents of persecution against Common Buzzards, principally poisoning, have been monitored annually for many years, and it is interesting to compare three-year averages for the UK as a whole from 1975 to 1989, and compare them with the average number of reports of poisoned Buzzards from 1995 to 1997, (See table 3). 

Table 3 Incidents involving Buzzard deaths throughout the UK

One difficulty with the data is that the number of reports of persecution is likely to represent a small, but unknown, fraction of the actual incidents taking place.

There can be little doubt that in the 19th and early 20th century, an active and unenlightened proliferation of gamekeepers kept the Common Buzzard population artificially low. The position in 1911 for example was that Worcestershire had the highest proportion of gamekeepers per square mile than any other Midland county (Brown 1970), and in Britain as a whole 20,000 were employed. This number had fallen to around 5000 by the early 1970's. Counterbalancing this to some extent has been persecution of predatory species considered to take gamebirds following a trebling, since 1961, of the number of hand-reared Common Pheasants in the UK (Elliott & Avery 1991).

One can perhaps conclude that persecution was once a far more significant factor than it is today.

The second possibility concerns the question of whether there has been a change in the availability of any particular food supply. In the UK the Common Buzzard depends largely on rabbits, particularly during the breeding season. A study of Common Buzzards on Dartmoor from 1956 to 1958, just after the outbreak of myxomatosis, found that the diet contained 345 mammals (120 rabbits and 134 voles) 73 birds, 15 reptiles, and some amphibia (Brown 1976). Thus, in terms of body-weight, Rabbits formed a very important part of the diet even at a time of depleted rabbit stocks. Common Buzzards will of course also regularly take carrion (often dead rabbits), and even invertebrates.

On a local basis there appears very little quantitative data which shows when, and to what extent, Rabbit numbers started to increase after the problems surrounding myxomatosis subsided. However, a very revealing piece of information has come from figures in the west country which looks at the population of rabbits, as indicated by the rabbit bags recorded in shoots (per J Birks in lit), (see Figure 2).

Figure 2. National Game Census data showing trends in rabbit numbers in the West of Britain, 1961 to 1995.

The graph shows the rabbit population exploding after 1985, which provides an interesting comparison with the evidence presented earlier based on reports in the West Midland Bird Club Reports. It is important to remember that Common Buzzards do not breed until they are at least three years old, so one would expect a delay of at least three years if more young Common Buzzards were surviving to sexual maturity, before these new Common Buzzards started to form breeding territories of their own. An increase in rabbit availability coupled with a lower level of persecution should have resulted in an increase in breeding pairs and perhaps a range expansion from the late 1980s.

The data available from the West Midland Bird Club Annual Reports during the late 1980s and early 1990s is unfortunately rather scanty, but suggests the increase in the number of sites from which Common Buzzards were reported may have gathered pace in the early 1990s.

If the expansion did happen after 1992 rather than around 1988, one possible reason for the delay might be found in the habit young Common Buzzards have of returning to the area in which they were hatched in order to breed. This mirrors the experience of ornithologists working on the reintroduction scheme for Red Kites where individuals are even more loyal to the natal area on reaching sexual maturity (I Carter pers comm). The result would be a slowing down of expansion into new areas. Eventually, however, sheer weight of numbers would drive the population to an eastward expansion of its range. 

Summary

Acknowledgements

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