An assemblage of 300 House Martins at Broadway, Worcestershire
P. F. Whitehead
On 26 May 2011 I received a telephone call that a large number of House Martins Delichon urbica (L.) had assembled in the Broadway area of Worcestershire at a spot where there was no recorded precedent. The assemblage amounted to some 300 birds, hawking invertebrates above Sloe Prunus spinosa L. thickets along a 100 metre embanked stretch of the old Great Western Railway mainline (SP03 70 m O.D.) during the afternoon.
The Cotswolds escarpment was marked on 26 May 2011 by meteorological instability as a fragmenting front tracking south-east created significant localised changes in atmospheric pressure. Frequent showers sometimes coalesced in a variable moderate to fresh gusty north-westerly flow. I reached the site at 1740 hours BST and observed some 45 House Martins feeding intensively above Sloe scrub between six and nine metres above the ground. As I watched them a further dense group erupted, apparently from ballast on the railway track, so that I was able to count some 105 birds in all; the following day some 100 martins were seen. Although rather late in the month, the implication would be that these were immigrants stalled by the front, making use of a food resource, believed to be small flies, itself assembled at one spot (Moss, 1995) by the north-westerly flow passing over the embankment providing some shelter in its lee (Turner, 1994). House Martins take a wide variety of invertebrates depending on their location including, for example, ants (Colston & Curry-Lindahl, 1986) and beetles (Whitehead, 1986; Osborne & Whitehead, 1988). It is possible that an emergence of flies from Broadway Sewage Plant was swept over the embanked railway line by the wind. This would explain the feeding concentration and although somewhat speculatory, numerous Barn Swallows Hirundo rustica L. were observed feeding at the sewage plant at the same time.
Although my mechanised data is incomplete I have no personal recollection of 300 House Martins massed in Worcestershire (noting that streams of autumn emigrants may reach significant numbers over a period of time), although regional large assemblages are documented by Harrison & Harrison (2005). However, a glance through the four most recent annual reports of the West Midland Bird Club shows that the numbers involved in such assemblages have shown a continuing tendency to reduce but that, interestingly, such spring observations are most often associated with episodes of climatic instability. It seems therefore that this observation warrants publication.
Colston, P. & Curry-Lindahl, K. 1986. The Birds of Mount Nimba, Liberia. British Museum (Natural History), London. Publication No. 982. pp. 1-129.
Harrison, G. & Harrison, J. 2005. The new birds of the West Midlands. pp. 1-496. West Midlands Bird Club.
Moss, S. 1995. Birds and weather. pp. 1-174. Hamlyn Ltd, London.
Osborne, P.J. & Whitehead, P.F. 1988. Coleoptera in the diet of House Martins in Worcestershire. Entomologist's Monthly Magazine 124:232.
Turner, A.K. 1994. The Swallow. pp. 1-128. Hamlyn Ltd, London.
Whitehead, P.F. 1986. Coleoptera in the diet of Worcestershire House Martins. Coleopterist's Newsletter 23:7-8.