Richard S. Turner, Ophélie J. D. Lasne, Kara N. Youngentob, Shukhrat Shokirov, Helen L. Osmond, Loeske E. B. Kruuk

In wild bird populations, the structure of vegetation around nest-sites can influence the risk of predation of dependent young offspring, generating selection for breeding birds to choose nest-sites with vegetation characteristics associated with lower predation rates. However, for researchers, vegetation structure can be difficult to quantify objectively in the field, which might explain why there remains a general lack of understanding of which characteristics are most important in determining rates of predation. Airborne Laser Scanning (ALS) offers a powerful means of measuring vegetation structure at unprecedented resolution across different spatial scales. Here, we combined ALS with 11 years of breeding data from a wild population of superb fairy-wrens Malurus cyaneus in south-east Australia, a species which nests relatively close to the ground and has high rates of nest and fledgling predation. We derived structural measurements of understorey (0-8 m) vegetation from a contiguous grid of 30 x 30 m resolution cells across our c. 65 hectare study area. We tested whether: (i) cells with nests differed in their understorey vegetation structure characteristics compared to those without nests; and (ii) the selection of these sites for nesting was adaptive, by assessing the effects of vegetation characteristics on rates of nest success and fledgling survival, and the subsequent probability of a breeding female having any reproductive success. We found that nest-cells differed from unused cells primarily in having denser vegetation in the lowest layer of the understorey (0-2 m; the ‘groundstorey’ layer). Understorey vegetation was also on average lower in height in nest-cells. However, relationships between understorey vegetation structure characteristics and breeding performance were mixed. Nest success rates decreased with higher volumes of groundstorey vegetation; as did fledgling survival rates, though only in nest-cells with lower height vegetation. Reproductive success was not influenced by any of the understorey vegetation structure characteristics considered. Our results therefore indicate that ALS data can identify understorey vegetation structure characteristics relevant for superb fairy-wren nest-site selection, but that nesting preferences are not beneficial under current predation pressures. Overall, our study illustrates the potential of using ALS to investigate how ecological processes affect behaviour and life-histories in wild animal populations.