Special thanks to Joan Morrison for contributing her time to be interviewed for our blog.
Crested Caracaras, as biologist Dr. Joan Morrison describes this species, are "sedentary and smart, and nesting pairs occupy a well-defined home range." While such traits make a Caracara what it is, it also means the species is not especially well-studied. Joan explains, "There's so much scientific interest in migratory species and the movement data that they produce. That's really cool. Frankly, the telemetry data that Caracaras produce are a little bit boring because they don’t move around much!"
Their resident, localized nature, Joan believes, may also make the Crested Caracara more vulnerable to extirpation, at least in Florida, where the population is isolated and relatively small. Without movement by individuals in or out of the south-central Florida population to, for example, the more widely distributed Caracara population in Texas, Florida's Caracaras suffer reduced genetic diversity. What's more, Caracaras in Florida face habitat loss as land conversion projects alter their preferred habitat.
Such factors underscore the importance of better understanding this captivating falcon. Questions about the Florida population of Caracaras have led Joan to devote more than 30 years of research to understanding the species’ life history, with special focus on the effects of habitat loss.
A Localized Species
When PTTs (Platform Transmitter Terminals) first emerged in the 1990s as a means to track and observe animal movement, many researchers heralded their groundbreaking ability to track migratory movement in particular. For Joan, however, this technology wasn’t particularly helpful for studying Florida Caracaras because they do not make long-distance movements. Because Caracaras are nonmigratory and occupy a limited range in Florida, "[The PTT units’ functionality within] a kilometer of accuracy just wasn't working for me, because Caracaras are very sedentary and have specific home ranges and hardly ever leave them," explained Joan.Data received from GPS/GSM transmitters can elucidate spatial relationships among neighboring Caracara territories. Other than the occasional excursion outside the generally used area, data show how faithful a Caracara is to its territory. (Nests are identified by red dots; other dots represent individual birds.) In areas where locations of neighboring birds overlap, there may be some clearing or other activity that favors Caracaras foraging there.
Around 2010, with PTT technology now more accurate and lightweight enough for Joan's research needs, she and a postdoctoral student tagged 8 Caracaras with PTT units, eager to obtain data. How did that go over with the Crested Caracaras? As Joan put it, "Most of the transmitters came off within a few weeks." Why? "The birds HATED them. They ripped them off and broke the antennas." Some species are just not suited for certain elements of telemetry, Joan explained. The external antenna was a required component of the PTTs for receiving a signal, but that antenna is what the Caracaras didn’t like. Failure of the Caracaras to accept the PTT technology resulted in a halt to her telemetry-based research, at least for a while.
With the emergence of GPS/GSM transmitters, however, Joan recognized an opportunity. GSM devices feature an internal antenna. "Without an external antenna to damage, these new transmitters were a promising alternative to use on the tag-destroying Caracaras."
The ES-400 features an internal antenna, making it suitable for outfitting on Crested Caracaras. Photo by LeeAnn Cooper.
Fortunately for Caracaras and for Joan, the new GPS/GSM units (some of her first units came from Cellular Tracking Technologies) proved successful. Even so, capturing and tagging Crested Caracaras requires an experienced person in the field. "The way that I put the backpacks on is so specific," said Joan, "because I know that they will try to take them off." Indeed, one tradeoff in banding and tagging an intelligent species is accepting that they will sometimes outwit their transmitters. She related, "Allopreening is a behavior in which a pair of birds will preen each other. It's a pair-bonding behavior and also an appeasement behavior. During allopreening, one bird can figure out how to remove the other bird's transmitter."
Allopreening, as demonstrated here by Black Vulture and Crested Caracara pairs, can result in transmitter removal. Photo by P. Raney.
In the event that a bird's transmitter is removed, recapturing the Caracara to retag it is nearly impossible. "It is extremely difficult to recapture a Caracara and put another transmitter on it," Joan explained, “because they remember how they were initially captured, and they know to avoid repeating the experience." Another barrier to successful transmitter performance can be feathers. "Caracaras have very long nape feathers that can cover the solar panel, so the units need to be offset so that doesn’t happen," Joan explains. "We asked CTT to alter the design a bit to account for this. When we first tag a bird, we also clip the nape feathers as additional insurance that the solar panel will receive sufficient charging."
This CRCA sports freshly clipped nape feathers. Photo by R. David Isley.
Private Land for Habitat
A view of the Crested Caracara's preferred terrain. Photo by Joan Morrison.
Her concern? As the number of land conversion projects and associated take permits increases, Crested Caracaras are increasingly forced to move in response to these changes in the landscape. As Caracaras are forced to relocate, they often establish territory on private land, such as ranches. Because there is often no or limited access to these areas, capturing and tagging Caracaras becomes even more challenging--and underscores why deploying transmitters, when possible, is vital for research.
Monitoring Florida’s Crested Caracaras has contributed to a better overall understanding of this understudied falcon, and research has provided many examples of the challenges facing the south-central Florida population of this threatened species.