ArticlePDF Available

Relative efficacy of 9-mm and 12-mm PIT tags for studying little brown myotis (Myotis lucifugus): a cautionary note. Bat Research News 62: 49-50.

  • Gray Owl Environmental Inc.


We implanted little brown myotis with 9-mm or 12-mm PIT tags. The percentage of bats that were detected within the year of tagging and in subsequent years was significantly less with 9-mm tags. The number of days that individual bats were detected within a year was significantly less with 9-mm tags. Use of 9-mm tags may lead to underestimates of return and survival rates.
© 2021 Bat Research News. All rights reserved.
Relative Efficacy of 9-mm and 12-mm PIT Tags for Studying Little Brown Myotis (Myotis
lucifugus): a Cautionary Note
Al Sandilands1 and Derek Morningstar2
1Gray Owl Environmental Inc., 1356 Lockie Road, Branchton, ON N0B 1L0, Canada, and
2Myotistar, 51 Silverthorne Drive, Cambridge, ON N3C 0B4, Canada
Passive integrated transponders (PIT) are
commonly used to monitor bat populations
(Garroway and Broders, 2007; O’Shea et al.,
2011) and are more effective than
conventional capture-recapture studies in
determining survival rates (Ellison et al.,
2007). We studied little brown myotis
(Myotis lucifugus) at a roost in a stone shed,
with two openings, near Cambridge, in
southwestern Ontario. Our initial purpose
was to study the demography and roosting
ecology of a population exposed to white-
nose syndrome, but our project provided an
unexpected opportunity to test results
obtained using two sizes of PIT tags.
We implanted bats with tags on seven
dates from 2015 to 2017. In May 2015, we
used 12-mm tags (HPT12; 12.5 by 2.1 mm,
0.12 g, BioMark, Boise, Idaho), but upon
recommendation of the Ontario Ministry of
Natural Resources and Forestry (OMNRF),
we applied 9-mm transponders (HPT9; 9 by
2.1 mm, 0.08 g) in July and August 2015.
During August 2015, we observed that some
bats had lost their 9-mm tags or that the
transponder did not register when the animal
was recaptured. After further consultation
with OMNRF, we again implanted 12-mm
tags in May, July, and August 2016 and July
2017. In all years, we positioned two cord-
type PIT readers (BioMark IS1001) around
each opening without restricting access by
the bats. The readers ran continuously,
except during power outages, collecting data
from 2015 until the end of 2020.
We marked individuals of all age and sex
classes, but only the sample of adult females
(89) was large enough for statistical analyses.
We implanted 24 adult females with 9-mm
transponders, 54 with 12-mm units, and 11
with both sizes. The double-tagged bats
initially were implanted with 9-mm tags in
2015, and the 12-mm versions were inserted
when the animals were recaptured in 2016 or
The readers detected 11 of 35 (31.4%) 9-
mm tags at least once in the year of placement
and/or a subsequent year (2015–2020),
compared with 50 of 65 (76.9%) 12-mm tags
(Χ12 = 17.93; P < 0.001). Number of animals
detected in a year subsequent to the year of
capture was 7 of 35 (20%) for those carrying
9-mm units and 40 of 65 (61.5%) for bats
with 12-mm tags (Χ12 = 14.14, d.f. = 1,
P < 0.001). For 9-mm transponders, mean
number of days between first and last dates of
detection within a year was 16.5 ± 7.7 (SE)
days compared with 69.3 ± 3.6 days for 12-
mm tags (β = 51.22; t75.8 = 4.32; P < 0.001).
Mean number of days detected within a year
was 2.2 ± 0.5 days versus 24.3 ± 1.9 days for
9-mm and 12-mm tags, respectively (β =
25.69; t65.1 = 4.50, P < 0.001).
Our results suggest that 9-mm tags do not
perform as well as 12-mm tags and may lead
to inaccurate conclusions about movements
of bats and underestimates of return rates.
This was probably due to a combination of
tag loss and lower detectability of 9-mm tags.
We documented loss of some 9-mm
transponders but no loss of 12-mm units. The
signal from the 9-mm tags appeared weaker
and occasionally could not be detected even
when the bat was in hand. Ousterhout and
Bat Research News Volume 62: No. 3
Semlitsch (2014) reached similar conclusions
in a study of movements by juvenile ringed
salamanders (Ambystoma annulatum). Those
authors determined that detection and
recapture rates increased with increasing size
of PIT tag, due to the longer detection
distances of larger units, and that detection
rates decreased when the long axis of the tag
was perpendicular, rather than parallel, to a
portable antenna.
This study was partly funded by the
Canadian Wildlife Service and the Rapid
Response Fund of the National Speleological
Society. The OMNRF issued the necessary
permits. We thank A. Alic, G. Buck, A.
Ceballos-Vasquez, R. Del Giudice, S. Fraser,
L. Greville, L. Haines, K. Hoo, S. Labrie, N.
Leava, O. Morningstar, L. Owens, R.
Perdiao, C. Risley, P. Ronald, M. Russel, B.
Talbot, and R. Valdizon for helping with field
work and decontamination of equipment. G.
Bettini conducted the statistical analyses.
Literature Cited
Ellison, L. E., T. J. O’Shea, D. J. Newbaum,
M. A. Neubaum, R. D. Pearce, and R. A.
Bowen. 2007. A comparison of
conventional capture versus PIT reader
techniques for estimating survival and
capture probabilities of big brown bats
(Eptesicus fuscus). Acta
Chiropterologica, 9:149–160.
Garroway, C. J., and H. G. Broders. 2007.
Nonrandom association patterns at
northern long-eared bat maternity roosts.
Canadian Journal of Zoology, 85:956–
O’Shea, T. J., L. E. Ellison, and T. R.
Stanley. 2011. Adult survival and
population growth rate in Colorado big
brown bats (Eptesicus fuscus). Journal of
Mammalogy, 92:433–443.
Ousterhout, B. H., and R. D Semlitsch.
2014. Measuring terrestrial movement
behavior using passive integrated
transponder (PIT) tags: effects of tag
size in detection, movement, survival,
and growth. Behavioral Ecology and
Sociobiology, 68:343–350.
... Other issues with PIT tags may include tag loss, movement within the body, or detection issues, which can be exacerbated in smaller tag sizes. 71 However, it is important to consider the body weight of the animal relative to the tag weight; this may be regulated, with some governments setting limits on the maximum chip weight as a function of body weight. 72 Therefore, researchers should consider the impacts of long-term PIT tags on bat physiology, such as the potential for reduced fitness due to tag weight or changes in behavior due to tag readers, though both of these issues have been demonstrated to be negligible for certain bat species. ...
Full-text available
Introduction: Field work with bats is an important contribution to many areas of research in environmental biology and ecology, as well as microbiology. Work with bats poses hazards such as bites and scratches, and the potential for exposure to infectious pathogens such as rabies virus. It also exposes researchers to many other potential hazards inherent to field work, such as environmental conditions, delayed emergency responses, or challenging work conditions. Methods: This article discusses the considerations for a thorough risk assessment process around field work with bats, pre- and post-occupational health considerations, and delves into specific considerations for areas related to biosafety concerns-training, personal protective equipment, safety consideration in field methods, decontamination, and waste. It also touches on related legal and ethical issues that sit outside the realm of biosafety, but which must be addressed during the planning process. Discussion: Although the focal point of this article is bat field work located in northern and central America, the principles and practices discussed here are applicable to bat work elsewhere, as well as to field work with other animal species, and should promote careful considerations of how to safely conduct field work to protect both researchers and animals.
Reproductive bats switch frequently among roosts to select the most advantageous microclimates and avoid predation or parasitism. Many bats use human-made structures, such as bat boxes and buildings, in areas where natural structures are less abundant. Artificial structures, which may be warmer and larger than natural structures, may affect bat behavior and roost use. We studied Yuma Myotis (Myotis yumanensis) and Little Brown Myotis (M. lucifugus) in artificial structures at two sites to understand how roost conditions and reproductive pressures influenced roost switching in maternity colonies in the lower mainland of British Columbia, Canada. During summer 2019, we used Passive Integrated Technology (PIT tags and scanners) to track daily roosting locations of individuals. Yuma myotis and little brown myotis used at least five roosts at each site and switched almost daily among roosts. Bats were less likely to switch from roosts that were 25–42°C and switch roosts during lactation, particularly when the young were nonvolant. Our findings suggest that reproductive female myotis that use artificial roosts seek out warm roosts to limit energy expenditure and speed up offspring development. We also found that bats boxes were not thermally stable environments and the behavior of bats reflected temperature variability. Land managers should ensure that multiple nearby roosts are available to maternity colonies, as reproductive bats require a range of temperatures and roost types during summer.
Full-text available
Movement behaviors have broad ecological and evolutionary implications, affecting individual fitness, metapopulation dynamics, the distribution and abundance of species, as well as gene flow and thus adaptation and speciation. However, movement behaviors such as dispersal, station keeping, and ranging are poorly understood in many taxa due to the incompatibility of traditional tracking methods with long-term observations. This is particularly true for small-bodied life history stages and species. While the introduction of smaller passive integrated transponder (PIT) tags and the development of PIT telemetry have removed some barriers, the trade-offs between different tag sizes are unknown. Through a series of experiments, we tested for effects of PIT tag size on detection, movement, tag retention, growth, and survival of a juvenile amphibian. We found no effect of PIT tag size on initial movement distance, survival, or growth; and all individuals retained their tag for the course of the experiment. Detection and recapture rates, however, were increased with PIT tag size. The orientation of the tag relative to the vertical axis of the antenna also affected the size of the detection field, which was 15.78–43.90 % smaller when the antenna was moved perpendicular rather than parallel to the long axis of the tag. We conclude that PIT telemetry is a suitable technique for marking previously untraceable species or life history stages and may offer insight into the behaviors of these individuals. Investigations using multiple PIT tag sizes should include this in statistical analyses to account for tag size biased detection differences.
Full-text available
We studied adult survival and population growth at multiple maternity colonies of big brown bats (Eptesicus fuscus) in Fort Collins, Colorado. We investigated hypotheses about survival using information-theoretic methods and mark–recapture analyses based on passive detection of adult females tagged with passive integrated transponders. We constructed a 3-stage life-history matrix model to estimate population growth rate (l) and assessed the relative importance of adult survival and other life-history parameters to population growth through elasticity and sensitivity analysis. Annual adult survival at 5 maternity colonies monitored from 2001 to 2005 was estimated at 0.79 (95% confidence interval [95% CI] 5 0.77–0.82). Adult survival varied by year and roost, with low survival during an extreme drought year, a finding with negative implications for bat populations because of the likelihood of increasing drought in western North America due to global climate change. Adult survival during winter was higher than in summer, and mean life expectancies calculated from survival estimates were lower than maximum longevity records. We modeled adult survival with recruitment parameter estimates from the same population. The study population was growing (l 5 1.096; 95% CI 5 1.057–1.135). Adult survival was the most important demographic parameter for population growth. Growth clearly had the highest elasticity to adult survival, followed by juvenile survival and adult fecundity (approximately equivalent in rank). Elasticity was lowest for fecundity of yearlings. The relative importances of the various life-history parameters for population growth rate are similar to those of large mammals.
Full-text available
Bats are among the most ecologically diverse mammalian orders. Most species live in groups for at least a portion of their life cycle and behavioural evidence suggests that individuals of many species live within complex nonrandomly assorting societies. However, rigorous quantitative characterizations of bat societies have been rare because of the difficulties inherent in studying these highly mobile, small, nocturnal animals. Here we use an automated monitoring system (PIT tags), telemetry, and recently developed analytical techniques to investigate the social organization (size, sexual composition, and spatiotemporal cohesion) and social structure (pattern of social interactions and relationships among individuals) of a colony of free-living northern long-eared bats, Myotis septentrionalis (Trouessart, 1897). Cluster analysis of HWI (half-weight association index) for all pairs and permutation tests indicate that colonies consist of multiple, nonrandomly assorting subgroups. A plot of the temporal persistence of relationships (standardized lagged association rate) showed that roosting groups dissociate. over periods of approximately 10 days after which subsets of individuals remain associated throughout the summer roosting season. A model representing a two-levelled social structure of long-term (whole summer) and short-term (up to 10 days) acquaintances best fit the lagged association rate. Subgroups were most cohesive during the lactation period, but we found no evidence for the effects of minimum nightly temperature on subgroup cohesion.
Full-text available
We compared conventional capture (primarily mist nets and harp traps) and passive integrated transponder (PIT) tagging techniques for estimating capture and survival probabilities of big brown bats (Eptesicus fuscus) roosting in buildings in Fort Collins, Colorado. A total of 987 female adult and juvenile bats were captured and marked by subdermal injection of PIT tags during the summers of 2001–2005 at five maternity colonies in buildings. Openings to roosts were equipped with PIT hoop-style readers, and exit and entry of bats were passively monitored on a daily basis throughout the summers of 2002–2005. PIT readers ‘recaptured’ adult and juvenile females more often than conventional capture events at each roost. Estimates of annual capture probabilities for all five colonies were on average twice as high when estimated from PIT reader data ( p̂ = 0.93–1.00) than when derived from conventional techniques ( p̂ = 0.26–0.66), and as a consequence annual survival estimates were more precisely estimated when using PIT reader encounters. Short-term, daily capture estimates were also higher using PIT readers than conventional captures. We discuss the advantages and limitations of using PIT tags and passive encounters with hoop readers vs. conventional capture techniques for estimating these vital parameters in big brown bats.