Contact: Wendel Sloan at 575.562.2253
PORTALES—Zach Jones, assistant professor of biology at Eastern New Mexico University, has contributed a chapter on the “Rough-legged Hawk” to the coffee table book “Raptors of New Mexico,” published by the University of New Mexico Press. ENMU professor emeritus Tony Gennaro also contributed a chapter on the “Mississippi Kite.”
The book's editor, Jean-Luc Cartron, asked Jones to write the chapter. Jones’ first field research projects in the 1990s used the Peregrine Falcon as a focal species, and he has always had a strong interest in predatory birds.
His research focuses on vertebrate organisms in general, and how wild populations of birds and mammals respond to an ever-changing human-altered landscape in particular. Most of his recent work has examined the influences of fire, grazing, introduced species, or urban development on various wildlife communities.
A number of companies, agencies and universities, including ENMU, sponsored the printing of the glossy, 710-page book. It retails for $50, and can be purchased at the ENMU Bookstore, as well as online at Amazon.com and Barnes & Noble.
Jones has seen the Rough-legged Hawk a number of times. “During the winter of 2009-10, they were fairly common near Portales, and, based upon my observations last winter, they were one of the most common hawks in the Portales vicinity,” says Jones. “However, that is not always the case because from year to year Rough-legged Hawk abundance is unpredictable in any single location.”
The species is relatively poorly understood compared to other species, most likely because it is a hunter of wide open spaces and has a tendency to avoid areas where humans occur at high densities, according to Jones. Also, human structures tend to favor other hawks, like Red-tailed Hawks that use power poles and buildings to hunt from, and the added competition for food in turn displaces Rough-legged Hawks from areas where they were previously common.
“Visually, the Rough-legged Hawk is distinct in having a large wingspan that can lead an observer to think they are seeing an eagle when in fact they are watching a Rough-legged Hawk,” says Jones, who received his Ph.D. from the University of Colorado. “Also, they have feathers on their legs, giving them the name ‘rough-legged.’"
Jones says, “The most exciting thing about them, to me, is that they remain mysterious. They breed in the far northern reaches of the globe, and spread southward in the Northern Hemisphere during winter looking for hunting grounds at northern temperate latitudes. However, they are unpredictable in where they go each winter, which makes studying the species quite difficult.”
The hawks come in a wide range of color morphs from mostly white to mostly dark brown, according to Jones. “Currently, the accepted reason for this variety is that the darker feather colors cost them extra energy each year when they molt, but the dark colors provide protection from microbes that degrade the feathers, which are more common in wetter climates. Therefore, the light-colored morphs occur in regions where the air is drier and the birds do not need the extra protection from microbes.”
The birds stay in the Northern Hemisphere year-round. They breed on the taiga and tundra in the summer, and migrate southward to mid-northern latitudes each winter, according to Jones. In New Mexico, they reach the southernmost counties in some years, but are most reliably found in more northern counties because the state lies at the southern extent of their winter distribution in most years. Some winters, none are found in New Mexico.
“They primarily feed on rodents and other small mammals in winter,” says Jones. “They also undoubtedly feed on snakes in the summer months, but they hunt by soaring to locate prey and then descend upon ground-based prey from above. They are not agile enough to regularly feed on other birds, unless they discover unattended nestlings in the nest of another hawk.”
Most likely, their dependence upon small mammals is what makes them unpredictable from year to year in the winter for most locations, according to Jones . Small mammals have frequent boom and bust cycles, alternating from highly abundant to extremely rare, and a Rough-legged Hawk is not likely to stay in any location when food is lacking. Their resulting winter distribution is that by mid-winter, only locations at northern temperate latitudes that allow hunting by soaring and also have high small mammal abundance are likely to have Rough-legged Hawks in that year.
“Overall, the hawk is an indicator species,” says Jones. “Its presence in winter informs us that small mammals are also abundant, which in turn means that many grass seeds are available for next year's coming rains and that mammalian predators like foxes, coyotes, and bobcats are having a good winter season, too.”
For more information, call Jones at 575-562-2723.