Seasonal variation in age, sex, and reproductive status of Mexican free-tailed bats

In North America, Mexican free-tailed bats (Tadarida brasiliensis
mexicana) consume vast numbers of insects contributing to the economic
well-being of society. Mexican free-tailed bats have declined due
to historic guano mining, roost destruction, and bioaccumulation of
organochlorine pesticides. Long-distance migrations and dense
congregations at roosts exacerbate these declines. Wind energy development
further threatens bat communities worldwide and presents emerging
challenges to bat conservation. Effective mitigation of bat mortality at
wind energy facilities requires baseline data on the biology of affected
populations. We collected data on age, sex, and reproductive condition of
Mexican free-tailed bats at a cave roost in eastern Nevada located six km
from a 152-megawatt industrial wind energy facility. Over five years, we
captured 46,353 Mexican free-tailed bats. Although just over half of the
caught individuals were non-reproductive adult males (53.6%), 826
pregnant, 892 lactating, 10,101 post-lactating, and 4,327 non-reproductive
adult females were captured. Juveniles comprised 11.5% of captures. Female
reproductive phenology was delayed relative to conspecific roosts at lower
latitudes, likely due to cooler temperatures. Roost use by reproductive
females and juvenile bats demonstrates this site is a maternity roost,
with significant ecological and conservation value. To our knowledge, no
other industrial scale wind energy facilities exist in such close
proximity to a heavily used bat roost in North America. Given the
susceptibility of Mexican free-tailed bats to wind turbine mortality and
the proximity of this roost to a wind energy facility, these data provide
a foundation from which differential impacts on demographic groups can be
assessed.

在北美地区，墨西哥游离尾蝠（Tadarida brasiliensis mexicana）会捕食大量昆虫，为社会经济福祉作出重要贡献。墨西哥游离尾蝠的种群数量因历史鸟粪开采、栖息洞穴破坏以及有机氯农药的生物富集作用而出现衰退。长距离迁徙与栖息洞穴内的高密度集群进一步加剧了这一衰退趋势。全球范围内的风力发电开发正持续威胁蝙蝠群落，并为蝙蝠保护工作带来了新的挑战。若要有效降低风力发电设施造成的蝙蝠死亡率，需获取受影响蝙蝠种群的生物学基线数据。本研究在内华达州东部一处距离152兆瓦工业风力发电设施仅6公里的洞穴栖息点，收集了墨西哥游离尾蝠的年龄、性别与繁殖状况数据。在五年的研究周期内，我们共计捕获46353只墨西哥游离尾蝠。尽管捕获个体中半数以上为非繁殖性成年雄性（占比53.6%），但同时也捕获了826只怀孕雌性、892只泌乳雌性、10101只泌乳后期雌性以及4327只非繁殖性成年雌性；幼体个体占总捕获量的11.5%。与低纬度地区同种种群的栖息点相比，该栖息点的雌性繁殖物候存在延迟现象，这大概率与当地较低的气温有关。繁殖雌性与幼体蝙蝠对该栖息点的利用情况证实，此处为一处育幼栖息穴，具备重要的生态与保护价值。据我们所知，北美地区尚未存在其他工业规模风力发电设施与大型常用蝙蝠栖息点距离如此之近的案例。鉴于墨西哥游离尾蝠极易受到风力涡轮机致死威胁，且该栖息点与风力发电设施距离极近，本研究数据可为评估不同种群类群所受的差异化影响提供基础。