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Measuring the Predator Context on Your Land to Manage Predation of Bobwhites
William E. Palmer, Ph.D. Tall Timbers Research Station
The interactions of predators and prey are fascinating areas of ecological research and one of the most challenging aspects of game management. While controversy exists among U.S. game biologists, in many parts of the world, researchers have determined that predators can limit game bird abundance (Newton 1998). In the U.S., the effect of predators on game bird populations likely varies regionally because of the impacts of weather on wildlife populations. Severe drought and heat in the southwest play an important role in game bird populations and may alter the effect of predators by disrupting predator-prey dynamics. These systems tend to produce “boom or bust” cycles for game birds like bobwhite. While game bird populations vary from year to year in the Southeast, the highs and lows are not as pronounced as in other regions. In the southeast our weather patterns are much more consistent from year to year. While we have droughts, they rarely last and entire growing season and are not usually associated with long-term stretches of blistering temperatures. Analysis of long-term population data by Tall Timbers indicates weather has a minor influence on annual fluctuations of bobwhites. Case in point, the record bobwhite populations maintained in the Red Hills during a record 3-year drought. Partly because of the milder climate, the predator community affecting bobwhites is also relatively stable from year to year (though epizootics occasionally impact some populations of predators). Other facts about the predator community combine to suggest predators may limit some populations of bobwhites, and possibly turkeys, in the Southeast. First, all of the predators I am referring to are generalists, with broad diet and habitat requirements. Their broad “niche” tends to insulate their populations from declines in one or two prey items. Second, the predator community is diverse, with many species capable of compensating for a reduced effect of one or more species in a given year. For instance, rat snakes and raccoons, two principal predators of quail nests over the past 2-years (documented by video) were insignificant this year on most study sites. Despite the reduced effect of snakes and raccoons this year, nesting success remained relatively unchanged as other predators, principally fire ants, bobcats and opossums increased their rate of nest depredations. Finally, this overall predator “context” can vary from relatively low densities to very high densities at different locations, depending on many factors, such as proximity to hardwood lowlands. Because this stable, compensating, complex predator community may be present regardless of the quail population, if a quail population declines, due say to habitat succession, predation under these circumstances can, in theory, limit their response to improved habitat management. That is the predators may exhibit equal or greater predation pressure on declining or low bobwhite populations. For further discussion of these ideas, see the series on predation in the Quail Unlimited Magazine. Simple demographics can help to explain this situation, as you can have the same survival and productivity to maintain a bobwhite population at almost any density. But, to move a population from low to high densities requires increases in one or more of the demographic variables (survival, nesting rate, nest success, etc.)
So if predation is likely to be a management issue, why should you assess the predator abundance instead of beginning to trap? First, predators are not always the most important limiting factor, habitat is. Second, predator management is relatively expensive to conduct and it is not just a one-time deal it is an on-going process. Third, as professional biologists, we should not advocate predator removal if it is not justified. Therefore, our ultimate goal is to be able to apply integrated pest management (IPM) ideas to predation management in the Southeast, or Integrated Predation Management. Integrated Predator Management is an approach to predation management that utilizes regular monitoring to determine if and when predator reductions are needed and employs physical, mechanical, cultural, biological and educational tactics to keep predator numbers low enough to prevent intolerable damage. Applied to bobwhite populations, if we had measures of predator abundances that we could use to “test for” the impact of those predators on bobwhite populations, then we could better justify both the need and expense for predator management. By definition, wildlife managers should take a holistic approach to managing predation. Removing important predator habitats can reduce the impact of predators without the need for expensive removals. Well-planned ground cover management can reduce predation on bobwhites, and presumably other wildlife (see Fig. 1). Supplemental feeding of bobwhites may increase survival by reducing foraging times and therefore exposure to predators. It also can improve nesting output, reducing the impacts of losing a single nest to a predator. Emigration of wildlife off your property from a deficiency in habitat should be considered an additional mortality factor (a loss to the population). All of these topics are important aspects of an integrated approach to predation management. In addition to indices of predator abundance, other information should be used. For instance, when appropriate habitat management practices are in place at the appropriate scales of time and space, and the population of interest has failed to increase, then this is a sign that some aspect of the predator community may be limiting your population.
In the southeast, there is a tremendous amount of data to support that predators may limit bobwhite populations, but most of it is circumstantial. At Tall Timbers, we are cooperating with researchers at Auburn University, University of Georgia and Georgia-USDA Wildlife Services, to rigorously test these ideas. In association with Quail Unlimited, several members of the Southeast Quail Study Group, a professional association of biologists, began a research project to assess how different predator “contexts” affect quail demography (See Fig. 2). A detailed description of the issue and the project is available in a 3-part series in the Quail Unlimited Magazine. In doing this project, we devised a simple, perhaps even crude, first step for assessing predator abundance. We do not believe that this is the ultimate answer, but rather a first step along a path of research, trial and error. Our goal is to refine measures of predator abundance to determine when the predator community may have exceeded thresholds and is likely to be limiting bobwhite population growth. In this article, I am going to explain how you can assess the predator context on your land. It is relatively easy and inexpensive to conduct these surveys. All you need is some sand, a shovel and rake and some predator attractants.
- Conduct the survey during October or November. To be consistent with our results, these times are best. However, you can use this technique whenever predators are active.
- Locate a scent stations at least 500 yards apart along unimproved roads, firebreaks or other linear travel lanes. Twenty-five stations will cover about 1000 –1500 acres. For smaller tracts of land, use fewer stations rather than packing in more stations. The distance between stations is important for maintaining some independence between stations. For larger tracts of land, say 5000 acres, use no more than 60 stations.
- Stations should be placed on alternating sides of roads within 5 yards of the road edge. Choose a location that is accessible and relatively easy to clear of vegetation and debris.
- Each station should consist of a 1.0 m diameter circle prepared by clearing vegetation. If the soil makes a suitable tracking surface then pulverize the soil to a depth of 1 inch. Alternatively, fine textured sand can be sifted onto the station to facilitate positive identification of tracks. We add mineral oil to the sand to improve the tracking substrate (see Fig. 3).
- Place 1 fatty acid tablet (FAS) in the center of each station. Researchers have shown that FAS tablets elicit a good response from coyotes, gray foxes and raccoons. We have good visitation rates from armadillos, bobcats and other mammals as well. Be careful handling the FAS tablets (please read the label!). FAS tablets are reasonably priced and available from:
Pocatello Supply Depot
238 E Dillon St
Pocatello, ID 83201
- Stations should be sampled daily for tracks for a period of 3 to 5 days. Therefore, set stations up on day 1 and check them the next 5 mornings before noon. Smooth sand or sift new sand each morning. Attempt to choose days where rainfall is not likely to be a problem. Ignore data from mornings where rainfall destroyed tracks.
- Record species and number of animals at each station. For instance, you may notice 1 raccoon and 1 opossum at the 3rd station.
- Count the total number of visitations by raccoons, foxes, skunks, opossums, armadillos and bobcats. Divide this number by the total number of useable (rain-free) station days. Therefore if you ran 25 stations for 5 days you would divide your total number of predators counted by 125 station-days (i.e., 5 days * 25 stations). If it rained 1 night, then you would divide your total number of predators (those counted on rain-free mornings only) by 100 station-days (i.e., 4 days * 25 stations).
Interpretation of Scent Station Results
The key to a predator survey assessment is knowledge of how the value obtained relates to demographics of the managed species. In cropping systems, counts of pests or signs of damage are used to make decisions about investing in a pesticide application. The information below should be considered a first stab at relating predator context to bobwhite demographics. This research is not yet completed, so it will continue to be refined over the next several years. However, we believe it will give a landowner some insights into the predator community on their property and may provide some guidance as to making decisions for predator management.
If visitation rates are below 10%, for example if 9 predators visited 25 stations over 4 days, (i.e., 9/100 * 100 = 9%) our data suggests predation is not a limiting factor on the property. If visitation rates are between 10 and 20%, then depending on habitat, predation may be limiting in some years. However, predation is probably not providing enough pressure on the population to stop the bobwhite population from expanding. If visitation rates greatly exceed 20%, our data suggest the bobwhite population may be limited by predation and predation management may be warranted. The goal of predation management is to maintain an ecologically functioning predator community. Not to eradicate predators from a property.
This technique is still considered experimental and data obtained from it should be used as a guide only. These relationships were developed on areas with good to excellent habitat over most of the property. Therefore, on sites with low amounts of habitat these relationships are not meaningful (additional research on agricultural landscapes is in the planning stages). Other indications of bobwhite population growth should be considered along with this protocol. Tracking population growth, either with dog searches or call counts is important for assessing how management is progressing. If bobwhite populations are responding to habitat management, then predation management may not be needed. If bobwhite populations are not responding to habitat management, and scent station visitation rates are modest to high, predation management may be an ecologically and economically viable practice for increasing bobwhite numbers. I believe the IPM approach is the correct approach to tackling the issue of predator management on private lands. It will require continued research and refinement to be fully efficacious. But, the IPM approach is defensible and makes economic sense for landowners seeking to improve abundance and diversity of wildlife on their lands. Because, if predators are not limiting your wildlife populations, then why spend precious dollars on controlling them?
Newton, Ian. 1998. Population Limitation in Birds. Academic Press, San Diego, CA.
For more information read the following articles: