Volume 45 Number 3 Fall 1998
H. Lee Stribling and D. Clay Sisson
Knowing the causes of mortality in a quail population and how this mortality is distributed over the course of a year is critical to proper management of that population. The field staff of Auburn University's Albany Area Quail Management Project in southwest Georgia has radio-tagged and tracked a large number of bobwhite quail (more than 2,200 individuals) during the last six years on some of the best quail land in the Southeast. Results of this AAES-sponsored study indicate that both management and environmental factors affect quail populations.
During the six years of this study, abundant information has been gathered on causes of quail mortality and the timing of that mortality through the year. Dating back to March 1992, a continuous sample of radio-tagged birds has been maintained on the primary study area (about 30,000 acres) representing a sample of more than 1,000 birds on that one study site alone. These data are from a high density, stable quail population and provide valuable clues about what can occur in an ideal quail situation.
Two primary areas of interest in the study are seasonal survival and causes of mortality.
Quail populations typically peak in the fall when the last broods are grown. Populations then begin to decline from predation, hunting, and other causes through the winter and spring until nesting season resumes.
In the AAES study area, population changes usually appear as long, slow, continuous declines in the number of adult birds over the course of a year (see Figure 1). Stated simply, for every 100 birds alive on November 1 of one year, only 20 will still be alive on November 1 the next fall. This translates into an 80% mortality rate, or what is referred to as an 80% turnover rate. The timing of this mortality is important. In the AAES study area, there appeared to be no single period with an unusually high mortality rate. This property averages carrying 60% of the birds through the end of the hunting season (February 28) and usually still has almost half the birds alive when nesting begins in late April. A textbook 20% of the fall population is still around the following fall. While this has long been considered a normal survival curve, recent research around the country has not backed this up.
The mortality rate through the nesting season in these studies was similar to observations in other studies; however, compared to the Georgia population, fewer birds made it into the nesting season. This obviously means fewer breeding birds, which results in fewer offspring produced. Therefore, in the Texas, North Carolina, and Missouri studies a more productive nesting season was needed just to replace their losses. The AAES study population was high density (more than one bird per acre) and was increasing during most of the six-year period studied.
Several possibilities may explain why overwinter survival is significantly higher in the AAES site. Most likely the high carry-over through the winter is due to a combination of abundant feed, ample high quality cover (protection from predators), a light harvest rate (the study areas annual harvest rate is only 10%), and mild weather.
Over the six years of the AAES study, the annual survival rate has varied little. While the average yearly survival has been about 20%, the range has only been from 15% to 23%. The lowest annual survival rate was seen in 1993 (15%) and was due to high mortality during the summer. The population coming into spring was very high and then severe drought conditions existed during the summer. The abundant quail population spent the summer in habitats that provided little cover and food due to dry weather, which made them more vulnerable to predation. When low summer survival was coupled with low reproductive output (also due to drought) the result was a population decline for the fall of 1993.
This study adds credence to the long standing belief of a 20% annual survival rate, at least in large blocks of well-managed quail habitat. While it is certainly true that most quail (80%) will die over the course of a year whether they are hunted or not, the timing of this mortality is critical.
On the Albany study area, 40 to 50% of the fall population was still alive at the beginning of the breeding season. In several other studies only 10 to 20% of the population was around when breeding began in the spring. Factors contributing to this high winter carryover are large blocks of good quail habitat, abundant feed, conservative harvest, protection from predators, and mild winters.
The other important aspect of quail mortality is not only when they die, but why. In the AAES study, predators appear to be responsible for almost all of the remaining annual mortality. Of the 452 known causes of death documented in this study, 239 (53%) were from mammals, 182 (40%) were avian predations, 25 (6%) were from harvest (hunting), and 6 (1%) were from snakes (see Figure 2). An additional 73 were from unknown or other causes, such as accidents and disease. The fact that mammalian predation was equal to or greater than avian predation on this study is worth noting. In most studies in the region (and on another AAES study site) the opposite is usually true.
Two peaks also occur in avian predation. The first occurs in April and is associated with several events. This is the time of year when the woods are burned, so available cover is minimal, and also is the time of the northern hawk migration. Combine this with increased movements due to covey break-up, as well as displaying and calling by males, and the result is high avian predation on quail. The second peak of avian predation occurs in December and directly coincides with the southerly hawk migration.
Snake predation is insignificant (only about 1%) but is interesting nonetheless. Most predation comes from canebrake rattlesnakes.
Male survival is slightly lower (mortality is higher) during covey break-up and initiation of breeding. This is due to their increased vulnerability to predators when they are displaying and calling. Male survival is slightly higher during the hunting season. This same phenomenon has been documented in other studies; however, it is not clear as to why it occurs. Very little difference in mortality occurred between sexes during the rest of the year.
Results of this study suggest that landowners cannot control all the factors that affect quail mortality, but they can enhance their quail populations by providing good quail habitat (nesting cover and brood raising areas), abundant feed (native, planted, and supplemental), and reducing predator populations if necessary.