The Indiana Bat Monitoring/Tracking Project

CQ VHF Summer 2005 bat trackingNote:  The Indiana Bat monitoring/tracking project concluded in 2005. This page tells the history. It was also the subject of my Homing In column in CQ-VHF Magazine for Summer 2005, titled "The Watertown Sodalis Squad -- An RDF Adventure."

On 20 January 2005, I received this request from Carl Herzog AB2SI of the New York State Department of Environmental Conservation:

"Our agency is currently preparing for two radio tracking projects that will take place from mid-April to early May 2005. We will be attaching transmitters to Indiana bats (Myotis Sodalis), an endangered species, as they leave their winter caves and we'll attempt to find them in their summer habitat out on the landscape. Both projects will be happening simultaneously and we are looking for volunteers (with or without equipment) to help with radio tracking.

"One cave is located in the Kingston, NY area. Previous experience suggests that some of these bats will fly to Orange and Dutchess Counties in NY. Others might fly anywhere within 300 miles, but most likely they will be found in lower NY, western CT, northern NJ, or eastern PA. The bats do not limit themselves to wilderness, but are often found in farm country or even suburban areas.

"The second cave site is in western NY near Watertown. We have no idea where these bats will go but, again, we do not expect them to travel more than 300 miles and probably less than 50 miles. This radius includes southern Ontario and Quebec - bats know nothing about national borders.

"Transmitters will be operating between 150 and 151 MHz. If you think of a single Morse 'dit' repeated every second or so, you'll have a good idea of what they sound like. Generally speaking, you'll need a SSB/CW capable receiver to hear anything. For folks who live in the right areas and are willing to devote a bit of time to this project, we might be able to provide receivers and/or antennas."


Out of 45 bat species in the USA, about one third are either threatened or endangered. There are millions of bats in New York state, but the number of Indiana Bats is only between 30,000 and 35,000. Myotis sodalis is the only federally-listed endangered bat in the state. The worldwide population for this species has declined drastically since the 1960's, dropping from about 800,000 down to about 300,000.

According to AB2SI, "Most other mammal species have been researched to a very significant extent, but bat biology so difficult to study that there are basic questions we don't yet know the answers to. It's only been in recent years that we've been able to get transmitters small enough to put on them so we can use radio tracking as a tool."

In other parts of the country, bats spend time underground year-round. In New York, the cave bats only spend the winter there. There are only nine caves and mines that in the entire state where Indiana Bats do that at present. Research indicates that this is because the bats are limited in the temperature range that they can tolerate during hibernation -- most caves are too hot or too cold.

Sodalis must be relatively undisturbed throughout the winter. If cave explorers were to wake them, even for a short time, they would use up their stored food resources and perhaps not last through the winter. This is not an issue in New York, because the sites are gated or on private property with no access to the public. That may explain why the New York population loss is not as great as elsewhere.

In my previous experiences with migratory bird studies, it was good to have a large number of participating hams scattered over a very wide area. Just being able to hear and log the tags was sufficient to help the researchers. But these bats were not flying cross-continent and exact locations would be important. What Carl needed was a team of intrepid trackers who were willing to scour the countryside. I posted Carl's request (above) on this Web site and hyped it on Amateur Radio Newsline and other ham news outlets. I was disappointed when my in-box didn't get many replies, but I discovered later that Carl had gotten all the help he needed, both from stay-at-home hams and those who would go out in the wild.

"We ended up with a total of five new field workers," AB2SI told me. "Three of them were on the project full time. They heard about it through your site and called my office to volunteer. When I found out that all of them knew radio propagation and had done a significant amount of RDF, I thought it would be a good match. We had some extra funding and we were able to hire them for the study."

Since Carl's office in Albany is a considerable distance from Watertown, it was difficult for the regular staff to work at the site for long periods. Having volunteers doing the ground work was a big plus. In addition to the on-site volunteers, I found out that many volunteers were listingin at home.

Remainder of the project log

More information from Carl Herzog AB2SI received March 25, 2005:   "Everything is proceeding according to plan. We don't expect the bats to begin to emerge from their winter quarters until approximately 15 April and we'll wait until they do so to attach the transmitters. The exact date will depend on the weather, more specifically temperature. The first warm pulse in the middle of April is usually what triggers things into action. Once that happens, things proceed at a fast pace. The first phase will involve 40 animals in the Watertown, NY area. All will be released in a single night. We will have a radio-equipped airplane circling the release site that night to give us an idea which direction they take. Our experience is that they orient themselves pretty quickly and seem to know where they are headed. It's not really feasible to follow them very far from the air, though. We really have little idea where these animals will go. We'll use 6 different frequencies to help us sort out some individual behavior.

"A few days later we will do the same thing for 20 more animals in the Kingston, NY area. Last year, bats from this site were located within about 30 miles of the release site, although we never found about half of them. Other folks who have tracked this species have reported distances traveled upwards of 200 miles.

"In both cases we will utilize a combination of air and ground-based searches in the succeeding days, hopefully guided by the information gained on the release night regarding the bats' initial direction of travel. The typical pattern is that they get where they are going in a day or two and then females begin to group together into maternity colonies of 50-200 individuals. They roost in trees and move from one tree to another every couple of days or so. Lots of ground follow-up is required (fun work for volunteers, that) as we keep track of the bats' activity. Among other things, we are interested in describing the kinds of trees they use, what types of places these tree are found in, etc. We expect the transmitter batteries to last about 3 weeks. The bats are just too small to carry any more than that.

UPDATE from Carl Herzog AB2SI received April 11, 2005:  

"In New York we have settled on a total of 6 different frequencies:

150.085 MHz
150.120 MHz
150.200 MHz
150.350 MHz
150.500 MHz
150.725 MHz

"We will have approximately 10 transmitters on each frequency during this year's project. Each transmitter exhibits one of three pulse rates: 30, 45 or 60 pulses per minute. The pulse rate will vary a bit with temperature but these three rates are sufficiently spaced we should be able to distinguish between them in the field. If you happen to hear what sounds like one of these transmitters, please record the pulse rate in pulses per minute as well as the transmit frequency.

"These transmitters are crystal controlled, but because of their minimalist design (no shielding, unregulated power supply, etc) they don't exhibit the frequency stability and clean CW note that crystal control usually implies. This means, unfortunately, that you can't count on finding the transmitter exactly on frequency. If you use a typical CW filter (500 Hz bandwidth) to boost your sensitivity, you might miss the signal unless you tune above and below the stated frequency. This is one of the reasons why professional wildlife receivers typically have a 2 kHz IF bandwidth, more like that used for SSB than CW.

"Furthermore, tolerances on the crystals means there is some deviation from the stated frequency. Most start out pretty accurate (within 1 kHz of the stated frequency at room temperature) but between the crystal variations, temperature drift, body-capacitance effects as the bats cram together in a tiny space, and calibration accuracy of the receiver's frequency indication, you'll need to allow for at least 2 kHz of error from the stated frequency. If your radio's dial accuracy is unknown, then even more allowance might be in order.

"One of our counterparts in Pennsylvania is also tracking Indiana bats this year from a site in western PA. He believes his bats fly east toward Eastern PA and New Jersey. All of his animals are on 172.1700 MHz. Any contacts on this frequency can be sent to me and I'll relay them as appropriate.

"Our experience is that these bats fly from their winter cave almost directly to where they spend the summer, arriving within a day or two after we let them go. They roost in trees during day, 8-30 or more feet above the ground. They will typically stick to one tree for a couple of days and then move to a different one in the same general area (less than a mile away, and often quite a bit less). This process of jumping back and forth between several trees will continue for the duration of our study. All of this means that if you don't detect them in one area during the first week then you are likely never going to. It wouldn't hurt to keep monitoring from that site, of course, but moving to a different location would be a potentially more productive use of your time.

"They fly at dusk to feed on insects every night that it's not too cold (50 F is about their lower limit) and your detection distance can increase dramatically at this time, although there will be fading due to multipath as they fly about. On a warm night they might be out any time before dawn, although at this time of year it tends to get pretty cold after midnight.

"Vertical RDF antenna polarization seems to work best when they are in the trees (during daylight), although not always. Horizontal polarization nearly always works best when the bats are flying, although they do roost periodically during the night so you can't count on that either. It's best to try both. If you have to choose, go with vertical during the day and horizontal at night.

"We use whip antennas when driving around and yagis for everything else. Even our airplanes have yagis on them. A three or four-element beam will at least double your effective detection distance over a whip but, of course, you have to aim it - fine for monitoring from a fixed site but if you are on the road you have to stop periodically to scan the antenna. I want a truck with a couple of stacked, long yagis on a rotator that can be operated from the driver's seat but, as someone once said, you can't always get what you want.

"Several folks have asked if FM gear can be used. The short answer is no, it's probably not worth your time. The transmitters do chirp a bit so you can often pick up something with an FM detector but the effective range is going to be greatly reduced. Pulse width is not well controlled but is something like a single morse 'dit.' There can be significant chirp which tends to spread the RF energy out a bit. Most hams wouldn't be happy if their CW signals sounded like the typical bat transmitter.

"Transmit signal strength varies a bit but to put things in perspective, we often pick up the signal from a mile over typical ground and 3-4 miles line of sight using a pretty sensitive receiver with a 2 kHz IF bandwidth and a 2-3 element yagi. This isn't great but it's what we have to work with. Many wildlife transmitters used for bears and other larger animals (even birds) are much more powerful.

"If you have mobile capability and attempt to pinpoint the location of any signals please respect private property rights. Don't traverse private property without the landowner's specific permission. If in doubt, err on the side of caution and refer all the relevant details to me."

UPDATE from Carl Herzog AB2SI received April 18, 2005:   "We sucessfully tagged 32 Indiana bats at the Watertown site last night (Sunday). The initial tracking from the air indicated that most flew toward the south but a substantial contingent went north as well, so Canada is definitely a possibile destination - if so it would be the first recorded instance of an Indiana bat north of the US border. Lake Ontario to the west is presumably an uncrossable barrier for them and we didn't see much indication that any flew east into the higher elevations. So far we have located several bats in the local area, less than 15 miles from the release site. Whether they will stay local or fly on farther in coming nights remains to be seen. Further updates will follow as time allows."

UPDATE from Carl Herzog AB2SI received April 20, 2005:   "The Watertown phase of the project is well underway. Many of the bats have been located in the area surrounding Watertown (within 15 miles radius). Ground followup on these animals will continue for the next 2-3 weeks. Others remain unaccounted for and searching far and wide may be necessary. At last report, our counterparts in Pennsylvania have sucessfully tracked at least two animals well over 100 miles from their release site, so long distance migration is clearly a possibility. The Kingston phase begins tomorrow (Thursday) with the scheduled release of 20 more animals. As mentioned previously, when we did this there last year all of the animals we found were in either Orange or Ulster Counties, but almost half escaped detection and could have flown to Connecticut, New Jersey, Pennsylvania or elsewhere. We will chase these animals for approximately the next 3 weeks as well. There will be numerous opportunities for ground followup over the next few weeks so if you are reasonably local to either site, let me know and we can probably give you an entertaining opportunity to apply your fox-hunting skills. If you lack equipment we usually have receivers and/or antennas available for loan. Reports generated by those monitoring from home will, of course, be greatly appreciated as well."

UPDATE from Carl Herzog AB2SI received April 24, 2005:   "Things have been hectic so it's been difficult to post an update until today (Sunday). We tagged and released 18 bats from the Kingston site on Thursday night. Initial indications were similar to last year in that the bats tended to fly south and southeast, with one lone individual bucking the trend by going North. Air monitoring the following day located 6 animals in Orange and Ulster Counties, but 2/3 of the animals escaped detection. Some could easily be in Connecticut, New Jersey or Eastyern Pennsylvania. Rain moved into the area late in the day curtailing our flights and yesterday was a complete washout for the planes, although ground crews attempted to get precise locations on those found from the air the day before. We may be able to get back in the air later today. A ham in Ulster county reported hearing one of our bats from his home and this was a new one for us. We failed to precisely locate it yesterday and will try again today. Other hams have figured prominently in our ground crews and have proven to be extremely helpful. One of the most interesting reports from the radio amateurs on this project continues to be that received from Harry, KS2D in Jamestown NY. He reports a signal that is on the 150.725 frequency which sounds like one of ours. If it turns out to be legitimate it will represent the farthest travel distance over which an Indiana bat has ever been tracked by radio. Harry and his cohorts are trying to pin down the location. It is possible, however, for realistic sounding signals to be generated by household electronics. Police scanners, for example, have fooled us a couple of times in the past."

UPDATE from Pat Browns WN8Z received May 7, 2005:   "We are still tracking and starting to enter the gray period where tiny batteries are just starting to fail. In the Watertown area we have started experiencing frequency drift. So if you are one of the hams with an ear to the radio, use the center frequencies and tune up and down from there. I've seen as much as a 900 Hz drift (most are drifting low). In the field we are finding that horizontal polarization seems to work best the majority of the time -- that was a surprise to all of us. We expect to lose the 60 pulse-per-minute transmitters first, as they are transmitting more often than the 45 ppm and 30 ppm transmitters. 14 hour days are the norm for us trackers. So rest assured anyone that is putting time in monitoring from home or elsewhere that we really do appreciate your reports!"

UPDATE from Pat Browns WN8Z received May 22, 2005:   "Wow - what an adventure! As of Thursday May 19th there was only one transmitter bat still sending out his signal from the Watertown, NY release - it is a 45 ppm signal and was still being heard a good distance away. Our tracking team has secured from active tracking and we will be checking on this last holdout as time permits. To all the amateurs and interested parties who have been following this project here, and especially to those who spent time listening for the tag signals, Your time and efforts were not in vain. Every day I talked with interested amateurs who devoted time listening from as far as 70 miles away and to others who were right in the Watertown, NY vicinity and every minute each of you contributed to this project was worth 60 or more to us in the field. Negative data is valid data. By letting us know that you heard no signals allowed us to concentrate our time in other areas. Thanks to each and every one of you."

UPDATE from Carl Herzog AB2SI received May 25, 2005:   "Pat WN8Z posted a nice update on the Watertown portion of our project a few days ago – thanks, Pat – and it is appropriate for me to do likewise. All of our transmitters from both the Watertown and Kingston sites are now dead. We had very good results overall, finding 16 of 18 bats from Kingston and approximately 26 out of 32 at Watertown. All of the bats that we found were within 40 miles of the release site and, yes, we did encounter a lot of false alarms triggered by spurious emissions from scanners. (As it turned out, almost all were on 150.725 MHz, which is a lesson for us in future studies: Do a better job of planning the frequency choices!) We didn’t get any animals in Canada, but one was close, only a few miles from the border. Nor did any of our bats venture into other adjacent states but, of course, we can’t be sure about those we didn’t find. As Pat hinted, the results are going to prove extremely valuable in our efforts to ensure the continued existence of this endangered species. Without going into details, there are some very immediate issues that these data will help us with. Echoing his comments, I’d like to also express my thanks to everyone who helped out on this project and especially to Joe KØOV for maintaining his web site and e-mail list. Amateurs contributed significantly to this project – frankly, we couldn’t have done it without you folks – and you can expect that others in the wildlife biology community will be looking to draw on your collective knowledge and experience in the future."

In the photos above, top to bottom:

THRDFS coverGo to Frequently Asked Questions about Wildlife Monitoring, including equipment suggestions

Go to Was That Really A Wildlife Tag?

HOMING IN logo Back to the Volunteer Wildlife Tracking page

Back to the Homing In home page

This page updated 20 May 2006