Project Accomplishments

Avian and Invasive Species Population Management




Develop information and methods applicable to avian populations of Wildlife Services' (WS) management concern and control techniques to reduce or eliminate invasive species.

Project Accomplishments 2010

Development of Control Methods for Burmese Pythons. In collaboration with state and federal partners, National Wildlife Research Center (NWRC) researchers at the Florida field station continued studies in 2010 to evaluate improved trapping methods for removing pythons. These ongoing trials are being photo of caged pythonsconducted within a large outdoor test pen at the station, where NWRC is maintaining pythons captured in south Florida. The patent-pending live trap developed by field station researchers is designed to reduce if not eliminate capture of nontarget animals. Evaluation of the trap under field conditions in south Florida is intended for 2011.

Assessment of Avian Radar and Satellite Telemetry for Tracking Vulture Movements. Radar and satellite Global Positioning System-Platform Transmitter Terminal (GPS-PTT) transmitters provide complementary information on the movements and behaviors of individual birds. The GPS-PTT tag provides a snapshot of altitude and location of a specific individual of an identified species at predefined intervals. The history of the individual is known because each transmitter has a unique identification code. The radar cannot identify individuals or even species but it provides continuous position reports (altitude and location) of birds within its detection range. By integrating data from the two sources, the behavior and movements of identified individuals (not possible with radar) can be continuously monitored (not possible with satellite tags).

In this study the radar detected 40% of the locations of vultures carrying GPS-PTT tags that were within five km of the radar. Most (75%) of the locations that were not detected were calculated to be above or below the radar's antenna beam. Speed and direction values recorded by the GPS-PTT tags and the radar were poorly correlated because the vultures were soaring and circling, which produced rapid changes in both azimuth and ground speed of the targets. Nevertheless, our findings show that combining these two techniques can allow monitoring of species that are of conservation concern where it is otherwise difficult to follow identified individual birds.

Efficacy of Oiling Eggs at Two Chicago Gull Nesting Colonies. Collaborations were conducted with WS operations in Illinois to document efforts alleviating bacterial contamination and consequent swim bans at Chicago's beaches by managing ring-billed gull production through egg oiling. Water quality data from the year before egg oiling and through the course of three years of egg oiling at 50%, 80%, and 80% of nests, respectively for 2007, 2008, and 2009, showed a reduction in the percentage of water quality tests exceeding bacterial contamination threshold at 18 of 19 beaches studied. Procedures for conducting gulls counts at Chicago's beaches during swim season were designed and analyzed. These counts were used to assess efficacy of WS-Illinois egg oiling program for ring-billed gull nests to reduce production. Three years of egg oiling at 50%, 80%, and 80% of nests, respectively for 2007, 2008, and 2009, showed a significant decline in the number of hatch-year gulls counted on Chicago's beaches through the course of the swim season, thereby reducing water contamination and bacterial counts.

photo of BOSSpecies-specific Hog Feeder. Feral hogs damage property, destroy native plant communities, cause agricultural losses, and carry diseases potentially threatening to domestic livestock. As yet, there are few methods to manage feral hog populations other than trapping and shooting.

Although feral hogs are hunted for sport, this alone is insufficient to keep free-ranging populations in check. One option under consideration is development of hog-specific feeding systems that would have the potential to deliver chemical sterilants, toxicants, or pharmaceuticals to feral hogs to reduce populations or their associated health risks. A major constraint to any such effort is limiting access of nontarget species to the bait intended for feral hogs.

We evaluated the responses of nontarget species, particularly black bear Ursus americanus, to the Boar-Operated-System (BOSTM), a feeder developed by scientists in the UK that has proven effective in trials in Texas and in the UK. There have been no previous trials of the unit, however, in areas where black bears and feral hogs co-occur. In the pre-treatment configuration (partially open), raccoons readily fed from the BOS. Often, before hogs ventured near the feeder, raccoons removed all of the bait from the tray. In the fully closed treatment mode, raccoons did not access the BOS. We encountered bears at each of the six study sites. Most bears learned quickly to spin the bait tray or shake the BOS unit to cause corn to fall from the feeder tray. Some bears did learn to lift the BOS cover with their paws, scrape the corn from the bait tray, and feed on it off the ground after closing the cover. Only one bear learned to raise the cover and then keep it open with its head as it ate the bait. We conclude that in areas without bears, the BOS will exclude nontargets. Where bears and feral hogs co-occur, however, a decision to implement the BOS should factor in the potential exposure of bears to bait intended for hogs.

Pentosidine Biomarker for Aging Birds—In a recent study, NWRC scientists and partners at the University of West Virginia identified a safe and effective method for removing and aging skin tissue samples from living birds. Scientists determined that a 6-millimeter-diameter piece of skin removed from the patagium (fold of skin between the wing and body of a bird) of living vultures and other similar-sized birds provides a sufficient amount of tissue for measuring the biomarker pentosidine. This small amount of tissue provides for reliable age estimation without impairing the birds' ability to fly. Studies that use bird banding often take a long time to acquire useable age structure data, whereas pentosidine has the potential to determine the age structure of a small population in a matter of months.

Researchers compared pentosidine concentrations in four skin-size samples (4-, 6-, 8-, and 20-millimeter-diameter biopsies) from the breast of black vulture (Coragyps atratus) carcasses. They also compared pentosidine levels from breast and patagium tissues of deceased vultures of unknown ages and monk parakeets ( Myiopsitta monachus) of actual, minimal, and unknown ages to document potential differences among skin collection locations. Pentosidine concentrations were similar between the four sizes of vulture breast skin. Pentosidine concentrations for the breast and patagium of vultures were similar, but in parakeets, pentosidine was higher in the breast than the patagium. The researchers then made pentosidine-based age estimates for vultures and parakeets using a general wild-bird age curve. Vulture age estimates were also made using plumage characteristics and a double-crested cormorant ( Phalacrocorax auritus) age curve. Vulture pentosidine-based age estimates appeared to correspond to plumage-based age estimates. Pentosidine-based age estimates for 88 percent of the known-aged parakeets were within 6 months of actual ages. Even though known ages were not available for all birds, scientists found a positive trend in pentosidine versus age for both species.

This information may lead to a reliable technique for determining the age of vultures and many other species of birds without the need for more costly and logistically difficult methods. The technique may also be applicable across a wide range of wildlife, potentially providing a valuable resource in the conservation and management of species of societal concern. NWRC is conducting similar research to develop a better understanding of cormorant demographics and impacts to catfish production in the southeastern United States.
Project Contacts: Michael Avery, Brian Dorr

[Insert photo 66A Population black vultures in trees.jpg]
Assessing Allowable Take of Migratory Birds—Black vulture populations are expanding throughout the eastern United States, causing an increase in associated problems involving livestock predation, property damage, and aviation strike hazards. Wildlife managers need a more reliable method to determine how many birds can be removed for damage management purposes without endangering the future sustainability of the population.

To help address this issue, NWRC scientists and biologists from USGS and FWS collaborated to develop a method for determining allowable take. Their analysis indicates that greater numbers of these birds could be culled than what is currently permitted without adversely affecting population levels. Called "Prescribed Take Level," the method developed in this study includes an estimate of the minimum size of the animal population, its maximum growth rate, and a variable determined by wildlife managers, based on the specific management objective and acceptable risk. Precisely estimating local vulture populations is difficult, due to uncertainties about the birds' lifespan and breeding habits. The researchers relied on annual bird-count data from the USGS North American Breeding Bird Survey and studies of radio-tagged vultures.

This method has great potential value for wildlife management efforts, as it can be adapted for use with other species and situations, such as the incidental take of depleted species, sport harvest, or nuisance control.
Project Contacts: Michael Avery, Bradley Blackwell


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