Use of Airborne Laser Scanning to assess effects of understorey vegetation structure on nest‐site selection and breeding performance in an Australian passerine bird

1 In wild bird populations, the structure of vegetation around nest-sites can influence the risk of predation 2 of dependent young offspring, generating selection for breeding birds to choose nest-sites with 3 vegetation characteristics associated with lower predation rates. However, for researchers, vegetation 4 structure can be difficult to quantify objectively in the field, which might explain why there remains a 5 general lack of understanding of which characteristics are most important in determining rates of 6 predation. Airborne Laser Scanning (ALS) offers a powerful means of measuring vegetation structure 7 at unprecedented resolution across different spatial scales. Here, we combined ALS with 11 years of 8 breeding data from a wild population of superb fairy-wrens Malurus cyaneus in south-east Australia, a 9 species which nests relatively close to the ground and has high rates of nest and fledgling predation. We 10 derived structural measurements of understorey (0-8 m) vegetation from a contiguous grid of 30 x 30 11 m resolution cells across our c. 65 hectare study area. We tested whether: (i) cells with nests differed in 12 their understorey vegetation structure characteristics compared to those without nests; and (ii) the 13 selection of these sites for nesting was adaptive, by assessing the effects of vegetation characteristics on 14 rates of nest success and fledgling survival, and the subsequent probability of a breeding female having 15 any reproductive success. We found that nest-cells differed from unused cells primarily in having denser 16 vegetation in the lowest layer of the understorey (0-2 m; the ‘groundstorey’ layer). Understorey 17 vegetation was also on average lower in height in nest-cells. However, relationships between 18 understorey vegetation structure characteristics and breeding performance were mixed. Nest success 19 rates decreased with higher volumes of groundstorey vegetation; as did fledgling survival rates, though 20 only in nest-cells with lower height vegetation. Reproductive success was not influenced by any of the 21