402 



THE ZOOLOGIST. 



The fact that open spaces are scarce except in the vicinity of 

 the rides must be taken into account in considering the positions 

 of the nests. 



Methods of Arrival and Departure. — In the case of the Willow- 

 Wren, as in most of our summer migrants, the male birds reach 

 the breeding-grounds in advance of the females. In this district 

 the first arrivals usually show themselves during the third week 

 in April, the average date being about the 19th of that month. 

 The filling-up of the area takes time, and is seldom complete — 

 even as regards the males— until May is in. The arrival of the 

 females commences about a fortnight after that of the earliest 

 males, and appears to extend, as a rule, over a shorter space of 

 time. In a favourable season the whole migration of both sexes 

 may be complete in about three weeks, but in a broken spring 

 this is otherwise. For example, in 1910, which had a par- 

 ticularly barren April, with an unusual prevalence of strong cold 

 north-west winds, the arrival of Willow-Wrens was exceptionally 

 irregular and protracted. Thus, while the first males reached 

 the wood on April 21st, only a third of the whole had settled 

 down by the end of the month, and the population did not 

 approach completion until May 8th-9th (there was evidence 

 elsewhere of males continuing to arrive as late as May 20th). A 

 close watch for females revealed none before May 15th, and the 

 bulk of them arrived with a rush between that date and the 

 18th. A table may make this arrival clearer : — 



Male birds 

 Date. Wind. present in wood. 



April 20 W. light — 



,, 21 N.W. strong 3 



,, 22 W. light 3 



,, 23 W. very strong... 3 



„ 24 W. light 3 



„ 25 N.W. light 3 



„ 26 N.W. strong 3 



27. 

 28. 

 29. 

 30. 



May 1 N.W. moderate 



2 „ 



S.W. 

 N.W. 



Male birds 

 present in -wood. 



6 



7 



6 



6 



. ,, „ .- 9 



.N.W. strong 9 



strong 



moderate 



3. 



4. 



5. 



6. 



7... 



8"!"".N.W. light 



y )» )) 



17 



20 



(May 10-18, weather quiet, with light 

 easterly winds. Female Willow- 

 Wrens mostly arrived May 15-18.) 



(The census of the wood was taken in the afternoons, as 

 through-passage males were frequently present in the early 

 hours of the day; almost invariably these had passed on by 

 midday.) 



