Bat Survey

I participated in an evening bat survey with subcontractors, for the purpose of being able to determine what species utilize a tract of land (presence/absence) on the Maryland western shore.  The resulting information will help guide natural resource management planning into the future.

Bat species within the genus Myotis have seen precipitous declines due to a disease known as white-nose syndrome (WNS), which especially affects the northern long-eared bat.  The methodology to survey for bats has been established by the U.S. Fish & Wildlife Service, and we followed their sampling survey protocols, including the use of:

AnaBat bat detection system that records ultrasonic bat calls using an ultrasonic microphone, and then using AnaBat software (zero crossing analysis) to determine bat species.


SonoBat bat detection system that records ultrasonic bat calls using an ultrasonic microphone, and then using SonoBat software (time, frequency, amplitude) to determine bat species.


Mist Capture Nets are hardly visible, very soft, black nylon nets with pouches, typically 20-feet tall by 28-feet wide with one-inch mesh that is hoisted on poles and stretched across a section of field or trail to live capture bat specimens.  Birds will fly into a mist net and get tangled and/or drop into the pouch.  Bats however are more discerning and may perceive mist netting as a spider web, and may often avoid the netting at the last second, turning away from the practically invisible netting.  The protocol required that we check the mist nets every 10-minutes.


I arrived on-site at 7:00 PM and left at 11:30 PM.  We went to our station, which was a confluence of dirt road trails and an open meadow, surrounded by forest and near water.


A photo of our staging area and meadow opening.  We installed an AnaBat receiver at the end of this field to record bat calls.


A close-up photo of the elevated Anabat microphone receiver housed in PVC piping.


We installed a mist net in the woods of this trail opening . . .


. . . and then another mist net within the woods of this trail.


This photo shows an example of a typical summer daytime roost, which is a bark flap.

According to the bat specialists that I worked with, the most common bat species in central Maryland include (in descending order of commonality)  big brown bat, eastern red bat, silver-haired bat, hoary bat, tri-colored bat (eastern pipistrelle), little brown bat, eastern small-footed bat, and then to a much lesser extent, the evening bat.

The big brown and eastern red bat love to feed on insects attracted by night lighting and feel quite at home in suburban and urbanized areas.


We also installed two SonoBat units along the forested trails to pick-up and record bat calls.


The SonoBat units had fresh batteries and the cards had plenty of memory for downloading the calls.

Most all bats (mammals) breed in the autumn and bear one or two young pups in June.  Most male bats tend to be solitary and breeding females may often congregate in maternity colonies of a few to up to 20 bats.  Most baby bats fly within three weeks and nurse for up to one-month.

Complaints about observed bats in and around homes and outbuildings usually occurs around the month of July, as juvenile youngster bats are first learning to fly and feed on the wing.  Bats hibernate in winter and require non-freezing structures such as, caves, tunnels, mines and the like.  Therefore most bats may migrate to summer grounds to breed, but require specific habitat requirements for over-wintering.

It was a clear, warm evening and this was night 3-of-5 for monitoring at two client locations.  The half-moon set as we performed our survey and the forest edges were ablaze with lighting bugs and the trill of frogs and insects.  We saw and heard dozens of bats, and we had one nearly hit the net while we were performing a 10-minute check, but unfortunately, we had no live captures while I was there.


This photo shows a flashlight inspection of a mist net during one of our 10-minute inspections.  All we caught were large insects, beetles and moths.

One neat feature of the AnaBat hand-held unit was a setting that allowed the inaudible sounds of bats to be altered so that we could hear them at an audible frequency.  It was a treat to watch bats feed on the wing along a tree line and constantly echo-locate non-stop as they flew by, as we heard them on the AnaBat recorder.


What a great way to spend the evening, but unfortunately no bats to photograph up-close and personal.

For general information on the bat species of Maryland, check out this following link:


On a related note, I just read an article, suggesting that bats avoid lighted areas at night.  See the following:

To maintain high biodiversity in cities, wildlife must be able to move between patches of habitat, which are often separated by paved surfaces, buildings and roads.  The bats studied in this experiment emerge in the evening from their roosts, often within residential housing areas, to feed on small insects in gardens, streams and other green spaces.  To reach these feeding areas they often “commute” along lines of trees, which are thought to provide protection from predators and high winds.

The researchers were studying the impact of artificial light on the Common pipistrelle that is found in parts of cities.  They wanted to find out whether the bats’ crossing behavior was affected by the distance between trees and the brightness of lighting within the intervening gap.  They found that the bats crossed via the darker parts of the gaps, but with sufficient lighting these gaps became barriers to movement.  Importantly, this barrier effect varied with the width of the gap in the tree line – bats would tolerate strong lighting in narrow gaps, but even low levels of lighting in larger gaps was enough to stop them crossing.

The ability to freely move around is key to individual bat fitness and resilience of the broader bat population.  Intensification and expansion of lighting could prove a real problem for bats as they move around a city.  Understanding the factors that affect movement between habitat patches is therefore important for urban species survival and conservation.  Our models predict that movement would be most restricted in the urban center, which might explain why even this common species of bat is rarely found in intensively developed areas.

We have focused our study on the Common pipistrelle, but the flight behavior of several other bat species may be influenced by artificial lighting.  More research is needed to explore the potential disruption of movement for other species.

See the article at: