Listening for Bats at Martin Van Buren's Lindenwald, 2023–2024

Bats at Lindenwald, then and now

An early tally of the animals around Kinderhook Academy, in Martin Van Buren's own day, lists "Vespertilio noctivagans" — surely a bat, perhaps a Silver-haired Bat. Bats were no doubt at least as varied, and probably more plentiful, around Lindenwald, Van Buren's home, in the mid-1800s than now. But their habits likely haven't changed much: any Big Brown Bats roosting in Lindenwald's cupola today may be the same species — even the descendants — of those roosting there in his time.

From February 22, 2023, to mid-June 2024, the Hawthorne Valley Farmscape Ecology Program recorded bats at Martin Van Buren National Historic Site to answer three questions: which species are present, which habitats they use and for what, and when they are active through the year.

A Silver-haired Bat (top) and a Red Bat (bottom), from J. De Kay's Natural History of New York (1842).

How bats were recorded

• Detectors: one Anabat Chorus ultrasound recorder in each of five habitats — swamp forest, crop field, pasture, a new orchard and wet meadow. Data were lost in mid-summer 2023, and the wet-meadow unit malfunctioned in summer 2024.
• Identification: the Sonobat software sorted more than 100,000 sound files; its most conservative setting identified 8,188 calls. Sample calls of each species were checked by hand. Some automatic IDs are surely wrong, but the overall patterns should hold for most species, especially Big Brown, Hoary and Tri-colored Bats.
• Myotis bats (the Little Brown Bat and its relatives) can't be reliably told apart by most calls — in one test, only about 25% of calls labeled Indiana Bat really were — so they were identified only to genus.
• Feeding buzzes — the rapid-fire calls a bat makes closing on prey — were counted to see where bats hunt.
• Caveats: call counts measure activity, not numbers (one bat circling a detector can out-call a stream of passers-by), and recorders can differ in sensitivity.

Which bats?

Of the nine species regularly found in the region, at least six were recorded:

The Tri-colored Bat (formerly the Eastern Pipistrelle), one of the region's rarest, turns up fairly regularly along creeks and ponds, including here; it was due to be listed as endangered in September 2024. Sonobat found no Northern Long-eared calls and only two possible Indiana Bat calls.

Where they hunt

• Activity ranked Big Brown, Silver-haired, Hoary, then Myotis and Red (roughly tied, and often confused by the software), with Tri-colored last.
• The orchard and north pasture were busiest; the wet meadow and cover crop field quietest.
• The swamp forest stood out: Big Brown Bats dominated there — surprising for a species said to prefer open habitat.
• Feeding buzzes peaked in the north pasture for Big Brown, Hoary, Red and Silver-haired Bats, then the orchard, where Myotis and Tri-colored fed as much or more. The wet meadow had far fewer — its calls sounded more like travel, suggesting bats may use the stream corridor as a route.

When they fly

• Bats were recorded in every month, but activity rose sharply in the second half of March in both years and seemed to drop steeply by early September (lost data leave late summer unclear).
• In winter, only Big Brown (which hibernates in buildings and wakes in warm spells), Silver-haired and apparent Hoary calls were recorded. Hoary Bats have never been confirmed wintering in New York, and on inspection most of these calls looked like Silver-haired — more evidence that some Silver-haired Bats now winter locally. On one late-February day, three passes came within minutes: one bat circling, or a small flock on the move.
• Warm springs: activity was higher in May 2024 than May 2023 at every site but the troubled wet meadow. By the program's own weather station, May 2024 averaged 5 degrees warmer (its average low 9 degrees warmer) — a hint that bats respond quickly to warm weather.

Then and now

Historical records of New York's bats are spotty, and names have changed; before mist nets and recorders, people mostly collected the odd bat they found, and a few dusk shooting surveys may have misjudged species mixes. Reading those "partial tea leaves":

• Big Brown Bat has probably increased;
• Little Brown Bat and perhaps Red Bat have declined — the Little Brown because of white-nose syndrome, first seen in 2006. It was the most common bat in the program's Columbia County recordings in 2005, nearly vanished after, and may now be recovering;
• Silver-haired and Hoary have probably changed less.

Probably a Red Bat, from Wilson's American Ornithology (1808–1814).

Climate may be shifting things: migratory Silver-haired, Hoary and Red Bats may be staying longer or even wintering here — or more monitoring may simply be catching what was always so. If they migrate less, fewer might die in autumn collisions with wind turbines, which now kill many of them. Some of these patterns may be one-year flukes; continued monitoring will tell.

Sources

Based on Conrad Vispo, "Preliminary Report on the Acoustic Monitoring of Bats at the Martin Van Buren National Historic Site," Hawthorne Valley Farmscape Ecology Program, published by the National Park Service; rewritten in hubnx's own words. The report dates the Kinderhook Academy tally to 1840 while citing it as Woodworth (1839), and its conclusion says activity ran through October while its results show a drop by early September; this page gives no year for the tally and follows the results. Its "Eastern Pipestrelle" is corrected to Eastern Pipistrelle. Its maps, charts and photographs by the Hawthorne Valley Farmscape Ecology Program are not reproduced.