Describing Purple Martin Movements in the Mid-Atlantic

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Introduction
Methods
Results
Acknowledgements
Describing Purple Martin Movements in the Mid-Atlantic
Katherine M. Bird1, Jeffrey J. Buler1, Ian Stewart2
1University of Delaware, Department of Entomology & Wildlife Ecology , 531 S. College Ave, Newark, DE 19716
2Delaware Nature Society, 3511 Barley Mill Road Hockessin, DE 19707
Despite their prevalence, the Purple Martin (Progne subis)
population declined 37% between 1966 and 2015. There is
little information about martin movement ecology during the
breeding season (Brown & Tarof 2020).
We monitored the breeding and post-breeding movement
phenology of individual Purple Martins using radio telemetry
and the Motus Wildlife Tracking System in the Mid-Atlantic
United States.
We captured 152 individual adult and juvenile martins among
four breeding colonies (most at Bucktoe Creek Preserve, PA
and Ashland Nature Center, DE) within nesting gourds during
three breeding seasons (April -July) of 2020-2022 (Fig. 1).
We banded birds with a USFWS aluminum leg band, tagged
them with a CTT LifeTag or HybridTag (434MHz) radio
transmitter via a leg-loop harness, and released birds at their
breeding colony (Streby et al. 2015a,b) (Fig. 2 & 3). Due to
some martins returning multiple years and some needing
replacement tags, this effort includes 178 individual yearly
telemetry records across 161 unique transmitters.
We created a >2,000 km2 “local” array of six Motus receiver
towers with overlapping coverage to allow for constant
automated monitoring of martin movement (Fig. 1). Receivers
uploaded detection data to a Motus database via cellular
connection.
We visually confirmed high rates of tag failure via antenna loss
within 30 days of tagging, which made determination of
movement phenology and birds fates difficult for most birds.
We used T-tests to determine differences by age and sex in the
duration of martin at the colony for the active nesting season,
the timing of post-breeding departure from the colony (i.e.,
leaving the local array), and post-breeding departure from the
Mid-Atlantic region for migration.
Brown, C. R., and S. Tarof. 2020. Purple Martin (Progne subis), version 1.0. In Birds of the World (A. F. Poole,
Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.
Streby, H. M., T. L. McAllister, G. R. Kramer, S. M. Peterson, J. A. Lehman, and D. E. Andersen. 2015a. Figure-eight
harness design and transmitter attachment.
Streby, H. M., T. L. McAllister, S. M. Peterson, G. R. Kramer, J. A. Lehman, and D. E. Andersen. 2015b. Minimizing
marker mass and handling time when attaching radio-transmitters and geolocators to small songbirds. The
Condor 117:249–255.
Conclusions
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•Across years, 108 radio tags/attachments failed within 30
days of deployment (60%). Of these, 58 were confirmed
antenna breakages (36%), 2 were confirmed harness
failures (2%), and 46 other tags presumably lost antennas
based on detection data patterns; initial consistent
detections followed by a distinct dead drop, or the tag
was never detected (43%).
•Only 67 tags performed as expected within a given year
(39%).
•The mean arrival date for returning birds was 29 April
(Range = 12 April –28 May) (n=6).
•No statistical differences between sexes for array
departure, total days detected, or region departure.
•Juvenile Purple Martins leave their colonies and the Mid-
Atlantic region about two weeks after adults
•Male martins spend more time near their colony than females
•Martin movements vary a lot by individual, and this is
confounded by tag durability
•Researchers should consider reinforcing the antennas of their
radio transmitters
Funding and support kindly provided by Delaware Audubon,
Delaware Nature Society, Delaware Ornithological Society and the
Purple Martin Conservation Association. We thank our generous
Motus tower hosts: Delaware Nature Society, Delaware Museum of
Nature &Science, London Grove Township, and Longwood Gardens.
•Juvenile mean fledge date was 16 July
(N=77, range: 9 July-22 July)
•The mean age of fledglings at array
departure was 54 days old (N=67,
range: 21-96