Cuckoos in Worcestershire - 2001

By Andrew Fraser

Introduction

For a number of years I have been increasingly concerned at an apparent decline in the numbers of cuckoos I hear in Worcestershire. When talking to other people they have confirmed this, commenting that they have declined in numbers and in some areas have disappeared altogether. I decided to ask members of the Wildlife Trust to record any cuckoos they heard or saw over the spring and summer of 2001.

Method

In the Trust's spring newsletter of Worcestershire Wildlife News I asked members to record and send me the following information on cuckoos:-

Results

Seventy-four different people sent in information, some single sightings, others a series of records, altogether totalling 147 separate sets of records. Some of the records sent in by different people were obviously the same birds recorded in the same place about the same time. In processing the records I ignored these duplicates, ending up with 107 records. 68 of these were single or in a few cases two records and 39 were three or more records of birds in the same place or extremely close together. These are plotted on the map.

I have made the assumption, based on no particular evidence, that where there were three or more records from the same locality a male cuckoo was holding a territory. Some of these territories were much more convincing with many records of birds calling, or pairs of birds or in one case a fledgling being fed by a dunnock. Obviously some of the single records may also have been birds holding territories, which were only recorded as someone "passed by". Others may have been birds trying out an area to see if they could attract in females and moved on when this proved unsuccessful. Having made this assumption I plotted the "territories" and the single records on the attached map. On only five occasions were a male and female cuckoos recorded together, on five occasions females were seen/heard separately and on only sixteen occasions were two males heard calling against each other.

This year the earliest male cuckoo was recorded on 9th April at Alvechurch and the last on 17th July last heard at Guarlford near Malvern

One of the main concentrations of potential cuckoo territories in Worcestershire is in the Salwarpe valley with three territories in close proximity, probably using the concentration of reed warblers, a favourite host, in the Droitwich Canal. The other is along the River Avon, again where there are good numbers of reed warblers. Elsewhere in the county they are dotted around rather randomly at a spacing seldom closer than three to four kilometres apart.

Distribution map of cuckoo records in Worcestershire 2001

Observers also sent me other information on cuckoos in Worcestershire. Phillipa Swanborough of Wyre Piddle sent the first dates on which cuckoos were recorded at her home by herself and her husband (table follows 1989-2001)

However, Phillipa's records of the first cuckoo of the year are eclipsed by Dorothy and Margaret Honeybourne, and prior to them, their father who started recording at Moorgate Road, Stoke Prior in 1916 when Margaret was born. Table below. This amazing recording marathon continues today. (See Worcestershire Record No 11, November 2001, page 11-12). This shows that the date for the first record of cuckoos is actually getting later averaging about 16th April in the 1920s whilst it is now nearer 26th April. Phillipa Swanborough also said they are arriving later. 60+ years ago they used to arrive around 12 April and "I think that the arrival of the cuckoo is getting later and later"

Data from Stoke Prior - see table

The prize for the most detailed records has to go to Elisabeth Jackson of Thorn Farm at Inkberrow who heard her first cuckoo this year at 6 pm on 24 April. On 13 May she first heard the calls at 4.40 am and the last one at 3.30 pm, in between she recorded the male calling 836 times! She heard the last male calls on 28 June. In between she heard and recorded thousands of male cuckoo calls, but no female bubbling calls. Does this mean that the male spent two months trying to attract a female and did not succeed during the whole of the two months?

Discussion

Lord and Munns (1970) recorded the cuckoo as "fairly numerous" across the West Midlands counties (Staffordshire, Warwickshire and Worcestershire). It was considered to be or breeding in five and probably breeding in twelve of the twenty-one 10 kilometre squares the book records in Worcestershire. This survey recorded it as definitely breeding in only one (young being fed) 10 kilometre square and possibly breeding in thirteen others. These records are based on un-coordinated records in one summer, the previous work by Lord and Munns was based on more co-ordinated recording over three years.

Lord and Munns suggest between 200 and 2,000 pairs for the West Midlands. Sharrock (1976) suggested national breeding densities of 5-10 pairs per 10 kilometre square would be a "modest" estimate, but obviously this is a considerable generalisation. National Common Bird Census records from British Trust for Ornithology surveys give a density of 1.34 pairs per square kilometre of farmland and 2.81 pairs per kilometre square of woodland. However the CBC records for the West Midlands show 4.8 pairs per square kilometre of woodland in the West Midlands. Harrison (1982) suggests that that a "regional population in the order of 4-6,000 pairs is probable". Gibbons et al (1993) also suggest that the average figure of 5-10 pairs per 10 kilometre square is likely across the country.

The Gibbons figures would give between 90 and 180 pairs of cuckoos for Worcestershire, the Harrison figures would give considerable more. Obviously the records I received are only a selection of the actual distribution of cuckoos across Worcestershire in 2001. However, few people recorded more than a couple of cuckoos, most heard birds from only one or two places. Many people have told me that they heard none last year and many others said the numbers have declined considerably, especially in recent years. I suspect therefore that at least in the central area of the county where many members live, many of the cuckoos holding territories have been recorded.

This creates a fairly depressing picture, but perhaps one that should not surprise us as it mirrors the problems of many more species of birds in the countryside. So what are the factors most likely to have caused the decline?

As a migrant, cuckoos are potentially at risk from changes in the over-wintering grounds in Africa or on the route to and from the UK. There has been no suggestion that this might be a problem for cuckoos, although it has certainly been for some other species such as sand martin.

One of the major changes in Britain has been the alteration in the management of the countryside due to intensive agriculture that has had a severe impact on many bird species. Tree sparrows, yellowhammers, grey partridge and many other species of birds of agricultural land have declined drastically as breeding sites and food supplies have declined. The main lowland hosts of cuckoo are dunnock and reed warbler with robin and sedge warbler used as alternatives. Some of the hosts have shown national declines in breeding numbers although dunnocks, the most important host, has had reasonable increases across the UK. Whether this is true in all farmland, is more difficult to judge. It is therefore difficult to show that declines in the main hosts have caused a reduction in cuckoo numbers.

The final factor may be food supply. Adult cuckoos feed mainly on large caterpillars of moths, species that have almost certainly declined drastically in the countryside due to intensive agricultural systems, but which may still be present in larger numbers in woodlands where more cuckoos appear to breed. The young cuckoos make enormous demands on their foster parents and it is possible that they are not able to provide adequate food for them to complete their development.

Whatever, the cause cuckoos must now join the depressing catalogue of species that has declined in the UK. Perhaps we should try to use it as a rallying call to persuade more people to manage their land in a more environmentally friendly manner. It would be so sad if future generations could not hear one of the most delightful and welcome sounds of the countryside in summer.

Acknowledgements

I am very grateful to all the people who sent me records or phoned them through to the Trust office. If anyone else recorded cuckoos last year (2001), but did not forward them I would still like to hear about them. They can be added to those that I have already received, provided they are accurate, to give a better picture of the cuckoos in Worcestershire last year. I need to know the information I mentioned at the start of this paper.

References