CONTACT: Julie Navejar

kajam03@tamuk.edu or 361-593-2590

HARRIS' HAWK STUDY HAS TEXAS A&M-KINGSVILLE

RESEARCH SOARING TO NEW HEIGHTS

KINGSVILLE (June 1, 2000) -- South Texas is a mecca for hawks. Because of their high visibility in the local landscape, raptors are particularly attractive to birdwatchers and aid in generating ecotourism dollars to local economies. Researchers at the Caesar Kleberg Wildlife Research Institute at Texas A&M University-Kingsville have long known that South Texas is an ideal region for hawks and have initiated studies to learn more about them.

One interesting hawk that is receiving a closer look by Christopher Appelt, doctoral student at Texas A&M-Kingsville, and Dr. Charlie DeYoung, dean of the College of Agriculture and Human Sciences and researcher at the Caesar Kleberg Wildlife Research Institute, is the Harris' hawk (formerly called the bay-winged hawk). The Harris' hawk is relatively abundant in southern Texas and is thought to play an important role in controlling rodent populations. It is a resident hawk and does not migrate.

At a distance, Harris' hawks appear chocolate brown, almost black, in color. They have rusty brown feathers on their upper legs and shoulder wing patches, bright yellow legs and bill, a white rump patch at the base of their tail and a white band a the end of its tail. "Harris' hawks are easily identified from other hawks in flight by their unique overall dark color and white rump patch and tail band," said Appelt.

Male Harris' hawks range in size from 1.2 pounds to 1.8 pounds. The female is larger, weighing between 1.8 and 2.6 pounds.

In 1998, Appelt entered the joint doctoral program in wildlife science between Texas A&M-Kingsville and Texas A&M University. Working with DeYoung, Appelt developed and initiated a study to learn more about cooperative behavior in Harris' hawks and to fill in the gaps regarding the general lack of information about this species in Texas. Their study is the first to examine ecological factors influencing group formation of Harris' hawks in southern Texas and is being conducted on private, state and Federal properties. Support for the study is being provided by the United States Fish and Wildlife Service, Rob and Bessie Welder Wildlife Foundation and Swarovski Optik North America Ltd.

Appelt said he will test several models for why the hawks cooperate and see which one best fits the Harris' hawks. "A lot of species of birds do things cooperatively, but almost no hawks do. I want to find out why the Harris' hawks work together. If we can understand the ecological factors that influence group formation, maybe the presence of Harris' hawk groups can be used to indicate the ecological health of a region."

"This hawk has a really interesting social behavior, in which three or more individuals work together in a cooperative effort for breeding and hunting activities,"Appelt said. "This is not typically found in avian predators, which tend to breed in pairs and hunt alone,"he added. Harris' hawk pairs breed for at least three to four years.

The cooperative behavior of these hawks makes them a favorite among falconers because they will hunt well together with humans, other hawks and even dogs, Appelt said.

Previous studies in Arizona and New Mexico have found that Harris' hawks often exhibit cooperative hunting and breeding with typically one to four auxiliary birds helping a primary pair. Auxiliary birds (both mature and immature individuals) are usually offspring of the breeding pair.

"Since Arizona and New Mexico have quite different habitat types than southern Texas, the importance of such behaviors in Texas populations is not clear. Also, because Harris' hawks in Texas are found in regions that vary ecologically, they likely exhibit different tendencies to cooperate under different environmental conditions," he said.

"We want to determine the relative numbers, distribution and habitat use of Harris' hawks across southern Texas, whether the tendency to form groups of different sizes varies across southern Texas and the ecological factors associated with the presence of various group sizes," Appelt said.

"By hunting cooperatively, Harris' hawks can capture relatively large prey like cottontail rabbits and jackrabbits, which together typically make up over 50 percent of their diet," he said. "They also eat rats, ground squirrels and other rodents and sometimes small birds and reptiles," he added.

"The Harris' hawks seem better able to capture larger prey because of their group behavior. They often search for their intended prey from perches, but they sometimes will all zero in on the same prey and get it," Appelt said.

"In some cases, older birds sit on a perch while the younger ones work to flush out the prey, putting them at risk from other predators," he added.

Preliminary findings suggest the Harris' hawks' cooperative behavior is influenced by habitats where they occur. "It seems that availability of tree cover is associated with whether or not groups are present," Appelt said.

This study will continue for another two years during which time firm conclusions can be drawn about the biology and ecology of Harris' hawks in southern Texas.

Appelt was born in Missouri but grew up in eastern South Dakota. He earned his bachelor's degree in biology from the University of South Dakota. He received his masters degree in fisheries with a minor in ecology from the University of Minnesota.

-TAMUK-