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Bat Roosting Census at Aziscohos Lake Maine:
First counts 2010

We continued our bat count at Aziscohos (see the 2006-10 summary) this spring. Arriving briefly on April 26 and shortly fleeing an approaching snowstorm on April 27, it was clear that bats were in residence but a count was not made. On May 3->5, counts were made by me and Davis Finch. The numbers of bats emerging were typical for those of early May in past years. As well, the timing of first emergence (8:15, 8:05, and 8:19, respectively) and the duration of emergence (~15 min) were similar to previous years. Davis observed that on May 4th, but not on May 3rd or 5th there seemed to be two size classes of bats, the smaller size comprising ~1/4 of the total, suggesting a smaller species roosting in the boxes. My guess is that the smaller were Little Brown Bats, while the larger were others in passage and simply joining the locals at appropriate staging areas.

With the assistance of Ed MacTaggart and Tess, I continued counts in the period June 9th ->June 13th . Initially the numbers were large and variable a typical feature of early spring which probably reflects migrating bats and/or bats that had not yet established a breeding site. However, by June 12th and 13th the numbers had stabilized at typical lower breeding colony numbers. There were a few significantly larger bats, maybe Big Brown bats, that do roost in the boxes on occasion. I was assisted in later counts in June by Gail Costello, Steve and Barbara Poulin and Dick and Karen Flagg, and later in June/July by Adele Miller, Aleksa Lutovsky, and Jeremy, and Brice Gust, the Lowes, Walter, Lana and Emily, who turned out to be a real bat enthusiast.

Nothing indicates changes in the bat numbers. It is possible that the composition of the population could vary (we have not yet definitely determined the roosting species or their seasonal frequencies). However the overall number of bats is unchanged for this period. That there has been no drop in bat numbers suggests that the white-nose disease has not yet become a factor in this part of western Maine.
Don Green,
July 8, 2010
Portsmouth, NH

 

Bat Roosting at Aziscohos Lake in Western Maine

The data I have collected on bat tenantcy over several years may be of interest as a baseline for those studying the spreading white-nose syndrome of bats in the eastern U.S.
I have counted bats roosting at my camp on Aziscohos Lake (T5 R3, Oxford County, Parkertown, Maine) since about 1990. The camp has 3 bat houses: a typical Peterson/Johnson design, and two Peterson/
Johnson designs halved on the diagonal. They are grouped together and face southeast with full sun exposure. Getting good counts under varying evening light levels has been a challenge to me. However, since 2006 I regularized my bat counts by using a sound transducer (Song-Finder Plus, Lena Industries) at 39.9 khz which allowed accurate directional counting of bats at all light levels. Most of the bats counted are probably Myotis lucifugus, but occasionally others are present.
Bats emerge reliably close to 30 min after sundown. The initial emergence period spans 14.9 minutes with a std. dev. of 4.7 minutes. Bats return from time to time during the evening and typically return to the roost an hour or less before dawn. Then they fly in front of the boxes in a large milling group at approximately my head height and enter the boxes in an orderly fashion that suggests to me a sort of “after you, my dear Alphonse” pecking order rather than a mad scramble to safety. Could roosting mates form up in flight and enter the boxes together?
Bat numbers average ~36/day for the months of June, July and August, and have shown no significant decline in the past five years. In contrast, day to day fluctuations in occupancy are common and can be dramatic (i.e., the std. dev. varies between 50% and 75% of the mean) reflecting a lack of strict fidelity to one particular site and the availability of many alternate roosting opportunities (including the ten bat houses I’ve placed with neighbors). Large increases have been noted during migration or, for instance, when a neighbor had his camp spray-painted and the bats rejected his camp and flew to mine doubling my count for a day. A cold snap can result in an increase in the roosting bat numbers and a heat wave can reduce the number. During a recent cool period, occupancy doubled from near 30 to 71, and as a heat wave took over, the number fell back to the thirties. This was then followed by recruitment flights as the parent(s?) enticed the young to their first flights and emergence number fell to 13. Presumably the parent had led them to a roost more appropriate for hot weather. Progeny increase the count by 15-20% in July and early August.

Due to my sporadic visitation schedule and the fact that weather conditions can interfere with my bat counting, the record is not uniform. However, the total number of observations in each year gives a good picture of population number. They reveal no significant reduction in bat occupancy at my camp in western-most Maine over the past three years.

July, 9, 2009
Donald M. Green, Ph.D.,
Professor of Biochemistry, Emeritus
277 Middle Rd.
Portsmouth, NH 03801

 

2006 Number Emergence
Emerging Period (P.M.)
6/6 25 8:37->8:46
6/29 52 8:45->9:03
7/11 66 8:38->8:58
7/13 16 8:37->8:55
7/15 19 8:34->8:53
7/16 29 8:37->8:50
7/24 56 8:21->8:44
7/28 36 8:28->8:45
8/7 28 8:15->8:30
8/8 30 8:14->8:38
8/11 47 8:05->8:22
8/18 29 7:59->8:10
8/19 17 7:40->7:55
8/21 8 7:45->8:00
8/22 18 7:53->8:05
8/23 15 7:48->8:08
9/1 19 7:29->7:45
9/2 22 7:26->7:42

2007 Number Emergence
Emerging Period
5/21 6 8:35->8:38
5/29 22 8:50->9:05
6/13 19 8:54->9:07
6/14 18 8:50->9:01
6/15 15 8:51->9:01
6/26 17 8:55->9:06
6/30 50 8:54->9:15
7/17 33 8:37->8:53
8/14 62 8:02->8:16
8/15 66 8:00->8:20
8/17 56 7:58->8:15
8/18 38 7:56->8:15
8/19 47 7:52->8:12
9/1 21 7:30->7:40
9/21 3 6:50->6:53
10/1 0 6:20->6:45

2008 Number Emergence
Emerging Period
5/24 85 8:00->8:45
6/7 89 8:40->8:52
6/8 4 8:46->?
6/9 6 8:30->8:53
6/25 32 8:55->9:05
6/30 48 8:54->9:15
7/1 41 8:55->9:12
7/15 26 8:37->8:53
7/16 40 8:36->8:53
7/17 33 8:35->8:53
7/31 57 8:07->8:21
8/1 69 8:15->8:30
8/2 66 8:09->8:24
8/5 63 8:06->8:23
8/14 39 7:48->8:10
8/15 39 7:54->8:05
8/17 30 7:52->8:00
8/18 31 7:47->7:54
8/19 17 7:45->8:00

 

 

2009 Number Emergence
Emerging Period
4/29 1 @ 8:13
5/ 6 32 8:11->8:28
5/8 23 8:20->8:30)
5/9 52 8:15->8:30
5/21 118 8:22->8:39
5/22 47 8:31->8:45
5/23 88 8:26->8:44
7/5 118 8:43->9:07

2010 Bats Emergence
Emerging Period
4/26 Many bats present-no count
5/3 29 8:15->8:30
5/4 63 8:05->8:34
5/5 44 8:19->8:34
6/9 96 8:37->8:54
6/11 74 8:34->8:59
6/12 28 8:45->9:00
6/13 24 8:37->8:58
6/30 56 8:44->9:04
7/1 37 8:43->9:02
7/2 71 8:43->9:02
7/3 71 8:40->9:01
7/4 34 8:46->9:05
7/5 30 8:52->9:07
7/6 13 8:53->9:07