Data from: Nest boxes increase reproductive output for Tree Swallows in a forest grassland matrix in central British Columbia

AbstractSecondary cavity-nesting birds depend on tree cavities for nesting and roosting, but many studies of these birds are conducted using nest boxes. Implementation of effective conservation strategies for cavity-nesting species such as nest-site supplementation requires careful comparisons of fecundity and other vital rates for birds using both natural and artificial nest site types. We compared breeding phenology, clutch and brood sizes, and fledging success of Tree Swallows (Tachycineta bicolor) nesting in tree cavities and nest boxes during 2001–2003 in British Columbia, Canada. Swallows using nest boxes initiated egg-laying and hatched young at approximately the same time as those in tree cavities (2 June, 23 June, respectively). Female Tree Swallows in boxes laid larger clutches (5.9 ± 0.9 eggs, N = 76) than those in tree cavities (4.2 ± 1.6 eggs, N = 67). The mean number of nestlings hatched was greater in nest boxes (5.2 ± 1.1 nestlings, N = 67) than in tree cavities (2.6 ± 2.0 nestlings, N = 58). Pairs in boxes were over twice as successful in producing fledglings (93.4%; 57 of 61 pairs fledged > 1 young) than those in tree cavities (35.8%; 19 of 53 pairs). Of those successful nests, pairs nesting in boxes fledged 5.1 ± 1.1 young (N = 57), whereas those in tree cavities fledged 3.5 ± 1.2 young (N = 18). Because cavities in nest boxes averaged 60% larger in volume and 1.8 cm wider internally than tree cavities, we suggest that increased reproductive output was correlated with boxes enabling a larger clutch size. In previous research, we found that Tree Swallows were a poor competitor with other cavity-nesting passerines for tree cavities. The addition of nest boxes may serve as an effective way to supplement local reproduction for secondary cavity-nesting bird populations by reducing competition for limited nest sites. This is especially true in regions where the availability of natural nesting sites is highly variable, and where species compete with many other cavity-nesting passerines using a similar ecological niche and nesting cavities., Usage notesPLOS_for_upload_TRES_cavboxNorrisetalData includes tree cavity and nest box information for 2001-2003摘要 次级洞巢鸟类（secondary cavity-nesting birds）依赖树洞进行筑巢与栖息，但当前针对此类鸟类的多数研究均借助巢箱开展。针对洞巢物种制定有效保护策略（如补充巢位资源），需对使用天然树洞与人工巢箱的鸟类的繁殖力及其他关键生命率开展严谨对比。本研究于2001—2003年在加拿大不列颠哥伦比亚省开展，对比了在树洞与巢箱中筑巢的树燕（Tachycineta bicolor）的繁殖物候、窝卵数、育雏数及雏鸟离巢成功率。结果显示，使用巢箱的树燕的产卵起始时间与幼鸟孵出时间，与树洞中的个体基本一致（分别为6月2日、6月23日）。巢箱内的雌性树燕所产窝卵数（5.9 ± 0.9枚，N=76）显著高于树洞组（4.2 ± 1.6枚，N=67）。巢箱内的平均孵出雏鸟数（5.2 ± 1.1只，N=67）同样高于树洞组（2.6 ± 2.0只，N=58）。巢箱内繁殖对的离巢成功率是树洞组的两倍以上：巢箱组93.4%的繁殖对（61对中的57对）成功育出至少1只幼鸟，而树洞组仅为35.8%（53对中的19对）。在成功繁殖的巢中，巢箱组的幼鸟离巢数为5.1 ± 1.1只（N=57），树洞组则为3.5 ± 1.2只（N=18）。由于巢箱的平均容积较树洞大60%，内部宽度宽1.8 cm，我们推测繁殖产出提升与巢箱可容纳更大窝卵数存在相关性。在既往研究中，我们发现树燕在与其他洞巢雀形目鸟类争夺树洞资源时竞争力较弱。补充巢箱可通过减少有限巢位的竞争，有效辅助次级洞巢鸟类种群的当地繁殖，这一点在天然巢位可获得性波动较大、且物种需与诸多生态位与筑巢需求相似的洞巢雀形目竞争者争夺巢位的区域尤为突出。使用说明 PLOS_for_upload_TRES_cavboxNorrisetalData 数据集包含2001—2003年的树洞与巢箱相关信息。