Taking a Ride in the Batmobile!
Interns in the Batmobile!
This week we did some more of our acoustic surveys for bats!
These surveys are conducted during the night time, starting right after the sun sets! In contrast to our Henslow's Sparrow surveys, where we had to be out every morning right before dawn, here we have to be out in the field and ready to go right after dusk!
The late nights are almost as difficult as the early mornings, but the main benefit of doing these bat surveys is that we get to do them from the comfort of an air-conditioned and mosquito-free refuge vehicle!
(It's actually really comfortable in there, so our biggest worry while working at night is not falling asleep!)
Given the time limit for completing these surveys (2 hours after sunset), the transects that we drive are typically between 20-30 miles. The transects are designed to go through the representative habitat types on the refuge that may potentially be used by our native bats.
The primary objective of these surveys is to perform a baseline inventory of bat species across our refuge in order to inform strategic habitat conservation initiatives. Big Oaks NWR perfoms these surveys alongside refuges all across the southeast regions as part of a much larger program intended to determine which bat species are present, where they're present, and in what amounts!
These are the species of bat that we are surveying for:
Native species of bat and their conservation statuses, provided by the Indiana Department of Natural Resources (DNR).
This project provides presence/absence data sets that will form the foundation for long term bat monitoring throughout the southeast, and will be the initial step towards determining if any of the species that we're surveying for need to be listed as threatened or endangered at the state or federal level.
To perform this great and noble undertaking, our batmobile is equipped with a bunch of fun (and expensive) little gadgets — not unlike the ones you might find on the crime-fighting vehicle of a certain caped crusader! We have three main pieces of equipment that make up our acoustical bat detectors, which I'll explain in detail down below:
First, we have our microphone! This device, as you can probably guess, is responsible for recording the sounds of the bat calls we hear while driving around the refuge. It is mounted on the roof of our vehicle by a suction cup, and records the calls from approximately a 50 ft radius around the vehicle while we drive our routes.
This microphone is specifically calibrated to capture high frequency (mostly ultrasonic) bat echlocations, detecting noise at a frequency of around 40 kHz! It is an extremely sensitive piece of technology, and is also prone to occasional drift. So shifts in frequency as small as > 2 kHz can dramatically affect the ability of our unit to detect and classify bat calls. As such, it's critically important that we calibrate and validate the microphone and data loggers before each field excursion!
Second, we have our GPS unit! It looks kinda like HAL 9000, and it's responsible for tracking our movements around the refuge and recording the precise location where each individual bat was heard. The ability to provide locational information regarding the survey route and subsequently overlay specific calls provides opportunities to explore habitat occupancy and to better understand changes of bat detections among various habitat types.
In some situations, changes in bat detection at the refuge level may directly correlate with significant habitat modifications (e.g., stand harvest, growth of reforested areas). Having this locational information helps us to understand how past habitat alterations have effected the population dynamics of specific bat species at a local scale, and may also help us to understand how future management actions may further impact them!
Last, we have our reciever! This is the device that logs all of the data recorded by the microphone and GPS unit and stores it onto our enormous data cards. Because of the technologies we use and the amount of locational and auditory information they're able to capture, a single night of surveying is enough to almost completely fill one of our 8 GB disks, and so they have to be processed and replaced between each route.
The mighty SanDisk! (part of the ANABAT reciever unit)
The technology that we use (the ANABAT SD2 system) is categorized as "full spectrum" software. This means that our devices capture the the entire the entire frequency range of bat echolocation calls while also capturing specific aspects of their calls (such as amplitude and harmonic measures). These specific traits of a bat's call allow our devices to assemble what's called a "call signature," which enables us to identify individual bats from a group of the same species. This is helpful for us to obtain an accurate count of the bats in a given area where there are many members of one species present and echolocating at the same time!
So! That was a lot of information all at once!
The main point to be made here is that each of these fancy toys has an essential part to play in ensuring that our data is collected thoroughly, accurately, and according to protocol.
The data collected here at Big Oaks — in conjuction with other agencies throughout the southeast — is necessary in order to get a clear picture of the distribution of bat populations across the region. Working in tandem with so many other refuges makes it essential to follow precise protocols when conducting our surveys and calibrating our equipment, so that we can ensure that all of the data we collect is valid and meaningful when compared to data sets from previous years, from future years, and from other refuges.
Being able to make these comparisons and observe these trends in population is essential in order to determine which species are in need of conservation and how best to conserve them. It's easy to lose focus of that lofty goal when you're riding around half-asleep in a comfy car all night, but I find that it's important to keep it in the back of my mind when my tired brain starts telling me to cut corners.
As with any of the other summer projects here at Big Oaks, the work is critically important to the conservation of our state's native wildlife. So therefore it's worth doing right!
Speaking of important work, I'll be back next week with some updates on our crawfish frog friends in the ponds. We have many tadpoles finishing their metamophoses, so things are already starting to pick up!
As always, stay tuned!