( 203 ) 



NOTES ON THE BREEDING OF THE MARSH- 

 WARBLER IN BERKSHIRE. 



BY 



A. STEVEN CORBET, b.sc. 



In iqzo I discovered a colony of Marsh -Warblers {Acrocephaliis 

 palnstris) breeding on an island in the Kennet Valley. The 

 island lies rather low and is partially swamped during the 

 winter months. In the summer a large number of small 

 willows are overgrown by nettles, osiers and goosegrass, while 

 a few ivy -covered hawthorn trees grow on the higher ground. 

 Generally the conditions seem to be ideal for a breeding haunt 

 of the SylviidcB. During late May and June nine nests of the 

 Marsh -War bier were found containing eggs. Built on to a 

 willow-stem and surrounded by tall nettles, the first nest was 

 discovered on May 26th. It was about three feet from the 

 ground and contained one egg, but was subsequently deserted. 



The second nest was found on June 2nd about ten yards 

 from the first. It contained two eggs and was in a similar 

 situation, but much longer (though not deeper inside) than 

 No. I. I had excellent opportunities for observing the parent 

 birds of the second nest, and later, my task was made easier 

 as one of them had a deformed bill. When they first left the 

 nest the melodious song was poured forth, but after half-an- 

 hour or so, they became anxious and flew to and fro in short 

 jerky flights. They did not appear to be shy and often 

 approached quite near to me. It was easy to observe them 

 singing on the branches of the willows overhead. Eventually 

 the female would return to the nest, although still under 

 observation. This nest was rather conspicuous, and on 

 June 7th the eggs had disappeared and the nest was deserted. 

 Later, however, the same birds built a new nest close to their 

 former site and successfully reared a brood. 



Except in two cases the other nests found were not strikingly 

 different from the two described either in situation or struc- 

 ture. One found on June 14th was built on some osiers 

 within a yard or two of the river and when approached the 

 birds generally flew across the river. 



The other nest calling for special remark was built in a fork 

 at the top of a small hawthorn bush. In this case the " basket 

 handles " were attached to two thin hawthorn stalks. The 

 nest contained one egg on June i6th and was the last built of 

 those under observation. 



From observations made on these nests at intervals of two 

 or three daj^s it appears that one egg is laid each day until the 



