Analysis of nest-records of the Willie Wagtail

Abstract

Five hundred and sixty-five nest-record cards of the Willie Wagtail are analysed. Information on habitat of the species is biased by the distribution and habits of obervers, but there is little suggestion that the bird usually lives near water. The nest is well known. Adults may dismantle nests for building later ones. Nests are found from below one to higher than fifteen metres, average almost exactly 3 m, but the distribution could be bimodal, below six and above seven metres, which would be caused by the structure of the native vegetation. Eggs are laid at an interval of 24 hours, usually between 05:00 and 09:00. The clutch is two to four eggs, average 3.1, but the sample is too small and scattered for significant annual or latitudinal differences to appear. Significantly smaller clutches are laid below 500 m than above and differences are significant between coastal, hilly and inland areas. The incubation and nestling periods are each fourteen days as a rule. Total breeding success is 58 per cent, apparently higher (63 %) in late broods after 30 November than in earlier (56%); C/3 is most successful in producing flying young (60%); but differences in success are not significant statistically. Pallid Cuckoos occasionally parasitize nests, usually unsuccessfully, presumably because there is no mimicry of eggs. The breeding season is from mid-August to late January, but mostly in October, November and December, which roughly corresponds to the times of first, second and third broods respectively. Differences in timing between different areas cannot be detected because of the scattered small sample, but laying probably starts two weeks earlier as a rule at Endunda, SA, than in ACT. The same nest is often used for two or three broods.

There are obvious difficulties in analysing data from cards from a very large area throughout which the climate is not the same each year. Climatic effects mask those of latitude, or latitudinal effects those of altitude. Concentrated data from a few widely separated places would be easier to compare and analyse.