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| Mangrove Cuckoo Cross Dike with visible antenna from a 2-gram satellite transmitter. Photo by Aaron Kirk |
ARCI’s biologists have
found that many conservation-related research questions can be answered best by
employing some type of tracking technology. Our study subjects, which include birds
of various families, sizes, and habitat associations, have benefited from this
approach. These include Swallow-tailed Kites, Short-tailed Hawks, Reddish
Egrets, White-crowned Pigeons, Crested Caracaras, Great White Herons, Peregrine
Falcons, Snail Kites, Southeastern American Kestrels, and Magnificent
Frigatebirds. Although telemetry’s use is limited somewhat by the essential
permitting requirement that the equipment not exceed 3% of a tagged bird’s body
weight, there has been no shortage of imperiled birds large enough to carry the
best-available tracking devices. Of course, this still leaves data needs
unaddressed for the many species of smaller birds requiring conservation
action.
Fortunately, the ongoing
development of smaller and more sophisticated telemetry devices has allowed us
to keep gradually unraveling the behavioral secrets of smaller and smaller
birds. One such species, the Mangrove Cuckoo, was of great interest to ARCI’s
researchers in 2015 when Microwave Telemetry Inc. (MTI), our long-standing
source for satellite-telemetry devices, asked us to test their prototype 2-gram
solar-powered transmitter – the smallest satellite-tracking device ever
developed. No one has ever determined the wintering destinations of Florida’s breeding
Mangrove Cuckoos, or whether they migrate at all. This is vitally important
information for this species, which is thought to be declining across its small
global range. To make such a project possible, MTI donated four of their 2-gram
transmitters to ARCI (they now sell for $4,500 each).
At the time, ARCI
already had been using MTI’s larger satellite transmitters with great success
to study the movements and ecology of Reddish Egrets in Florida, including a
population on the J. N. “Ding” Darling National Wildlife Refuge (NWR), Sanibel
Island, Florida. This declining species is one of the relatively few birds
considered seriously threatened by the Florida Fish and Wildlife Conservation
Commission. The Ding Darling NWR has been a very receptive and supportive site
for our egret studies, and they were particularly interested in seeing ARCI
conduct Mangrove Cuckoo research to expand on results of prior cuckoo research
and to tackle questions about seasonal movements and nesting ecology using this
amazing tracking tool.
From August 2015 to
February 2018, we safely deployed MTI’s four donated 2-gram satellite
transmitters on Mangrove Cuckoos inhabiting Ding Darling NWR. Although
transmitter lifespans have been relatively short (likely due to the vulnerability
of the tiny radios and their fragile antennas), we received over 12 cumulative months
of reliable data from the first three birds. Virtually all the satellite fixes
for these three birds were on Sanibel Island, suggesting that long-distance
migration might not be occurring.
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| Mangrove Cuckoo Indigo East just prior to release, showing the 2-gram satellite transmitter. |
The only exception was a
movement in early April 2016, at the start of the nesting season, by Indigo East, a bird that had
over-wintered on the Refuge after we tagged it the previous November (tracked
birds are named after their capture location). In this case, Indigo East quickly traveled six miles north,
across a wide channel, and settled in a small area within the mangrove forest
along the western shore of Pine Island. Here it remained until we stopped
receiving data two months later. Had it moved there to nest?
This intriguing
behavior, although inconclusive, suggested that Mangrove Cuckoos wintering on
Ding Darling NWR may indeed move elsewhere when it comes time to nest, but the
distances may be very short. Was this a rare exception, or is such behavior the
rule? Do birds that breed on the Refuge move southward off of Sanibel Island for
the winter? How many Mangrove Cuckoos nest on the Refuge, and how productive
are they? As is usually the case, new information led to still more questions.
We recently received our
most important results to date. Cross Dike,
the fourth and final Mangrove Cuckoo we tagged with a donated transmitter (last
February, as a wintering bird) made a sudden move northeastward on a track
similar to that taken by Indigo East
two years before (see Figure 1). Furthermore, both birds moved during the same
week in April. The only difference was that Cross
Dike traveled an additional six miles across a second channel before
settling in the broad mangrove forest on the western shore of Cape Coral - a
total of 12 miles from its wintering area on Sanibel.
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| Figure 1. Early breeding-season movements of two satellite-tracked Mangrove Cuckoos from established winter ranges on Sanibel Island, Florida. Indigo East (white) moved to Pine Island on 6 April 2016 and remained at least until early June, when data transmission ceased. Cross Dike (red) moved to Cape Coral on 12 April 2018, where the bird remains as of this update. |
Obviously, we are
working with a small sample of tagged Mangrove Cuckoos. However, we now have
highly consistent movement data, on fine time and spatial scales, from these two
study birds whose tracking periods have bridged the wintering and breeding
seasons. This is very exciting!
Given our very exciting
recent tracking results for Mangrove Cuckoos from Ding Darling NWR, we are
hoping to expand ARCI’s tracking studies of this species both in scope (to include
more tracking, plus nest-finding and monitoring) and geography (to other
Florida populations, and eventually to Cuba as part of our long-term
collaborations with University of Havana faculty and graduate students). At the
moment, we are awaiting a decision from Ding Darling NWR’s staff on a proposal
they requested for expanding our current Mangrove Cuckoo research on the Refuge.
ARCI is grateful to Microwave
Telemetry, Inc., and particularly to Dr. Paul Howey, for their very generous
contribution of the essential transmitters for the first phase of the Mangrove
Cuckoo study. We also thank Refuge Manager Paul Tritaik for permission and
logistic support for conducting this work on the
Ding Darling NWR. The Refuge staff is dedicated to carefully
managing this public conservation area’s diverse and sensitive resources with
the best available information. The fundraising and outreach efforts of the Ding
Darling Wildlife Society (the Refuge’s illustrious “Friends” organization), and
the support of Sanibel donors Judy Samelson and Bill Schawbel, have been
instrumental in the project’s success. We also are grateful to ARCI’s universe
of followers and supporters for their willingness to share in and support our
common mission.
We look forward to updating
all of you on our progress, and to sharing what we learn as this exciting
project unfolds.
