|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.
|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.
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.