Aerial insectivore populations have declined significantly across Canada for the last fifty years. Although there are several suggested drivers of these population declines, including agricultural intensification, not all species show similar spatiotemporal population trends. Therefore, comparing interspecies differences in breeding productivity on the breeding grounds is vital to understand what is driving population variation among aerial insectivores. We examined breeding productivity and phenology in relation to habitat, weather, and insect availability for two co-occurring swallow species, Tree Swallow (Tachinyeta bicolor; −2.79 regional annual trend index) and Barn Swallow (Hirundo rustica; −3.33 regional annual trend index) over four years on the southern coast of British Columbia, Canada. We found only minor interspecies differences in breeding productivity (brood size, fledge success) comparing first broods, although the Barn Swallow is double-brooded, suggesting higher potential productivity than in the Tree Swallow. However, Tree Swallows had larger clutches, earlier lay dates, and more rapid cumulative laying than Barn Swallows. There was little effect of habitat on breeding productivity or phenology for either species, and we found no significant difference in total insect abundance between crop and pasture habitats. Overall, our study suggests there is little interspecies variation in breeding productivity for first broods between these co-occurring aerial insectivores in British Columbia. Given the higher propensity for double brooding and no differences in brood size or fledging success, Barn Swallows in this region may, in fact, have higher annual productivity than Tree Swallows, despite a more steeply declining regional population trend, suggesting that declines are caused by factors operating outside the breeding grounds or during post-breeding.

中文翻译：

---

两种共同发生的空中食虫动物在繁殖物候和生产力方面的微小种间差异

在过去的 50 年里，整个加拿大的空中食虫动物种群显着下降。尽管这些人口下降有几个建议的驱动因素，包括农业集约化，但并非所有物种都显示出类似的时空人口趋势。因此，比较繁殖地繁殖生产力的种间差异对于了解是什么推动了空中食虫动物的种群变异至关重要。我们研究了与栖息地、天气和昆虫可用性相关的两种共生燕子物种树燕（Tachinyeta bicolor；-2.79 区域年度趋势指数）和家燕（Hirundo rustica；-3.33 区域年度趋势指数）的繁殖生产力和物候学) 在加拿大不列颠哥伦比亚省南部海岸的四年多。尽管家燕是双亲繁殖的，但我们发现与第一代相比，繁殖生产力（孵化大小、羽化成功率）只有很小的种间差异，这表明其潜在生产力比树燕更高。然而，树燕比家燕有更大的离合器、更早的产蛋日期和更快的累积产蛋。栖息地对任一物种的繁殖生产力或物候几乎没有影响，我们发现作物和牧场栖息地之间的昆虫总丰度没有显着差异。总体而言，我们的研究表明，在不列颠哥伦比亚省这些同时发生的空中食虫动物之间，第一窝的繁殖生产力几乎没有种间差异。鉴于双育的倾向较高且育雏大小或羽化成功率没有差异，该地区的家燕可能，