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Predator/Prey Relationships

In parts of their range, fluctuations in bobwhite populations are driven by weather to a large degree. Severe heat and drought can reduce recruitment and survival resulting in population crashes. Similarly, severe winter weather can decimate quail numbers. Over time the average density on an area is much reduced even if some years produce outstanding bird numbers. In the southeast, severe weather influences bobwhites occasionally but our research shows that only rarely is weather severe enough to cause more than a 30% decline from year to year. A tropical storm dumping 18” of rain may cause both adult, egg and chick mortality and reduce quail numbers in one event but effects of weather are typically subtle. Weather influences migration of bird flocks which influence the overwintering range of Cooper’s hawks which prey on bobwhites. Cooler and wetter summer weather may reduce chick survival resulting in lower fall populations. During la Niña years the early summer becomes too hot (> 98 degrees) and dry and both nesting and chick survival are reduced which impacts the most important hatch of the year (June).

Rather than weather, the interplay of habitat and predation play a much larger role in bobwhite demographics in the Southeast.  Quail live as part of a complex food web in the Southeastern U.S. From Cooper’s hawks, to corn snakes and cotton rats, quail, their eggs, and their chicks are eaten by dozens of predator species and a handful of others not typically considered predators, including rarely deer and squirrels. The Game Bird Program at Tall Timbers recognizes that to understand bobwhite population dynamics they must be studied as part of a larger ecosystem, including habitat, predators, disease, genetics, and of course weather.  Historically, relatively little research has been conducted on predation and bobwhite populations. We have made predation a focus of the lab: not just through predator control type studies, but by considering the process of predation and how it relates to habitat, food resources, and the temporal and spatial variation in both predators and alternative prey. Managers often express concern that predation negatively effects bobwhite populations and are interested in what measures can be used to reduce predation. As such, we have spent over a decade conducting research to understand how predation influences bobwhite populations and what management can do to minimize the impacts predation may have on a population. A partial list of our studies includes:

Predation and Survival

Cooper’s hawks very in abundance on quail lands in relation to habitat, prey base, and weather patterns.

Cooper’s hawks very in abundance on quail lands in relation to habitat, prey base, and weather patterns.

Bobwhite populations are very sensitive to adult survival rates. We know because we have the longest running band-recovery project on any game bird in the world.  Over 30 years, the average annual survival rate of bobwhite on Tall Timbers is about 0.20, or 20% of bobwhites alive 1 January will on average be alive the following 1 January (link to long-term banding study). However, this has ranged as low 7% and as high as 35%. As survival increases and decreases over time so do bobwhite populations. The explosive numbers of bobwhite in the Red Hills in 2002 and again in 2010 followed 3 years of high survival rates. In these years premiere quail plantations averaged over 10 coveys seen per hour of hunting for the entire season! Unlike areas of the bobwhite range where winter weather or severe drought can affect bobwhites, in the deep southeastern U.S., predation largely drives the changes in survival rates.

A major predator of quail in the Red Hills and Albany Area is the Cooper’s hawk.  Why is it that some years we see significant predation by these bird hawks and in other years we have very manageable predation? One hypothesis we have been working on for 10 years is the effect of another prey species, the cotton rat. Cotton rats demonstrate a cyclic population cycle in the Red Hills. Once thought to be a nest predator and a species that attracted predators to quail nesting areas, today we recognize that cotton rats are an important buffer prey species.  We have monitored their densities on Tall Timbers since 2002 and discovered some interesting relationships. In years when cotton rats are prevalent, predation on bobwhite is lower than in years when cotton rats are scarce.

Rats and QuailCotton Rat

Rats and Nesting

Rats on TTRS

 

As a quail manager we need to consider the importance of a broad prey base to “buffer” quail from predation to help sustain higher survival rates which demographically drive bobwhite numbers.  This effects how we burn (link to burning under management section) and manage timber (link under management section) and decide to supplemental feed (link under management section) or manage nest predators (measuring predator context link). 

Cotton rats also appear to influence the success rate of quail nests and the nesting rat of hens.  How so?  Well, we surmise that as cotton rat abundance peaks then nest predators such as snakes are more likely to prey on cotton rats and spend less time foraging for other prey items, such as quail nests.

So if more cotton rats are better what can be done to increase their abundance?  One important management factor is supplemental feeding.  Spreading supplemental grains across upland habitats helps to boost rat reproduction and increases populations significantly.

Managing the predator-prey cycle to benefit bobwhite populations, or other wildlife populations, requires skillful habitat management, care with burning, timbering, among other management actions to tip the balance of demographics in favor of bobwhites.  We are now researching how to use ecological indicators to predict when management activities will provide the most bang for the buck.  For instance, predicting low survival rates will allow managers to reduce harvests and avoid excessive population declines.