Southwestern spotted bats carry the most genetic diversity among 121 bats sampled over two millennia

A spotted bat is hard to count. It is nocturnal, an agile flier, and it roosts alone ^[2]. A field survey that finds fewer of them may be recording a real decline, or it may simply have missed them. Genetic data does not depend on spotting the animal. "Genetics allows us to see patterns of connectivity, isolation and long-term persistence that would otherwise remain hidden, providing information that can directly inform conservation planning," Walker said ^[9].

The appeal of this study is its depth in time. Museum specimens collected between 1904 and 1991 sit in the middle ^[4]. Behind them are six bats from a northern Arizona cave, with conventional radiocarbon ages of roughly 120 to 2,100 years before 1950. Ahead of them are contemporary specimens from 1994 to 2025 and bats captured alive ^[4]. In principle, that lets researchers ask whether today's bats carry less diversity than their predecessors did. A headcount of a solitary night flier cannot answer that question.

The old end of the sample is thin. Six of the 121 bats are ancient ^[3][4], about 5% of the total ^[14]. The other 115 ^[15] are split between the museum and modern periods. Many of the modern specimens came from a single cave, a sampling bias the authors list as a limitation ^[7]. Walker said the combined samples "allowed us to reconstruct a much broader picture of how spotted bat populations have changed through time" ^[13]. The press account does not give the split between periods or diversity figures for each one, so whether spotted bat diversity has fallen since 1904 cannot be checked from it.

The result it does report is geographic. The team described genetic structure, variation and relatedness across the range and found differences between northern and southern populations ^[6]. "One of the most important findings of our study is that spotted bats in the southwestern United States harbor the greatest genetic diversity across the species' range, making this region a critical reservoir of evolutionary potential for the species," Walker said ^[5]. Northern populations, she said, "appear to have lower genetic diversity and may be more vulnerable to future environmental change" ^[10].

The north-south contrast is a correlation with geography. The authors say further studies are needed on how specific human disturbances affect dispersal and population dynamics ^[8]. North American bats face threats including habitat loss, climate change and white-nose syndrome ^[12]. The authors' advice covers every kind of population they found. "Our integrative approach across temporal scales highlights the conservation importance of preserving genetically diverse core populations, vulnerable leading-edge populations and isolated relict lineages," the authors said ^[11].

I'd treat the Southwest finding as usable for setting priorities now, on one condition. That condition is knowing which region the over-sampled cave sits in, because a modern sample drawn mostly from one site can shape how diverse that region appears ^[7].