R. Scott Lutz

RED IMPORTED FIRE ANT IMPACTS ON NORTHERN BOBWHITE POPULATIONS

The stability of Northern Bobwhite (Colinus virginianus) populations in Texas, where high density polygyne red imported fire ants (Solenopsis invicta) account for >50% of all (S. invicta) colonies, has been cited as a reason to repudiate impacts by this exotic species on Northern Bobwhite. We used two approaches to investigate the relationship between red imported fire ants and Northern Bobwhite. In the first approach, we used correlation analysis to compare Northern Bobwhite abundance trends, determined from Christmas Bird Count data in 15 Texas counties, before and after fire ant infestation. Before red imported fire ant infestation, no significant trend in Bobwhite abundance existed (r = -0.355, P = 0.314). After fire ant infestation, Northern Bobwhite abundance declined and was highly negatively correlated with years of infestation (r = -0.867, P < 0.001). Bob- white populations from 16 uninfested counties in Texas revealed no trend over a 27-yr (1966-1992) period (r = -0.081, P = 0.688). In the second approach, red imported fire ant populations were reduced on five 202-ha study areas in the Texas Coastal Bend; autumn Northern Bobwhite densities were monitored for 2 yr on those reduced areas and five untreated areas. By the 2nd yr, Bobwhite autumn density was higher (P = 0.028) on areas where red imported fire ants were suppressed. We concluded that polygyne red imported fire ants were negatively impacting Northern Bobwhite in this region of Texas.

Optimal group size and northern bobwhite coveys

Abstract Northern bobwhite, Colinus virginianus , form social units, called coveys, during the nonbreeding season (approximately September–April). Because the evolutionary advantage of this behaviour is generally unknown, we used controlled group size manipulations within an aviary to investigate whether group size influences (1) the time that the covey spends feeding, (2) the percentage of the covey that is vigilant, (3) the overall vigilance of the group and (4) the time to predator detection. We found that increasing group size increased the time that coveys spent in an exposed feeding area, reduced individual vigilance, improved group vigilance and decreased the time to detection of a potential predator. Additionally, we used experimental reductions of wild northern bobwhite coveys to test whether groups size influences (1) individual and covey survival, (2) daily movement in maintaining covey size and (3) mass change. We conducted field research on 12 independent 259-ha study areas (6 control plots and 6 treatments, where 60% of the population was removed) in east-central Kansas, U.S.A. between 9 November and 31 January, 1997–2000. We radio-marked 386 radiocollared individuals that comprised 137 groups on the study areas. Covey size did not differ between or within years or treatments ( X ±SE: 10.98±0.22 individuals). Our results indicate that a stable group size existed between 1 and 22 individuals, with 11 being an optimal group size. Small coveys (1–7 individuals) had lower group persistence and individual survival, and used increased movement to create or join larger groups where survival was higher. Large groups (15–22) had lower individual survival, increased group movement and individual mass loss. Density-dependent feedbacks (e.g. lower survival and increased competition) may have lowered larger coveys to a stable size. Our results suggest the regulation of an optimal covey size of 11 was promoted by high group persistence, low group movement, improved feeding efficiency, improved individual predator detection and improved individual survival. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

WINTER SURVIVAL AND ADDITIVE HARVEST IN NORTHERN BOBWHITE COVEYS IN KANSAS

Abstract We examined how harvest affected natural mortality rates and how the dynamics of northern bobwhite (Colinus virginianus, hereafter bobwhite) covey membership might affect the additive nature of harvest. We conducted repeated searches for coveys and radiomarked all coveys found on 12 259-ha study areas in east-central Kansas, USA. We simulated a harvest in 6 randomly selected areas each year during November–January, 1997–2000, by trapping and removing 60% of bobwhites in each covey. We used flush counts and radiotelemetry to measure harvest effects on natural mortality rates, overall winter survival, covey size, and densities. Observed natural mortality rates of radiomarked individuals were similar between harvested (50.6 ± 4.3%) and unharvested areas (52.1 ± 4.7%). Estimated winter survival was 47.9% on the unharvested areas and 20.9% on the harvested areas. Harvest did not affect the number of coveys, average covey size, or density of bobwhites, indicating that coveys coalesced through local movement. Our results indicate that harvest is additive to natural mortality and suggest that local movement to maintain optimal group sizes can mask the true effect of harvest on observed densities in small areas.

EFFECTS OF RED IMPORTED FIRE ANTS ON RECRUITMENT OF WHITE-TAILED DEER FAWNS

We investigated the effect of red imported fire ants (RIFA; Solenopsis invicta) on an index of white-tailed deer (Odocoileus virginianus) fawn recruitment (doe:fawn ratio) on 10 200-ha plots in the Texas Coastal Prairie during 1991-93. Five of the plots received treatments of the fire ant bait AMDRO© (Am. Cyanamid Co., Wayne, N.J.) during April and October 1991 and May 1992 to reduce RIFA populations. The remaining 5 plots served as untreated comparison areas. Populations of RIFA were reduced (P < 0.10) on treated study areas during deer fawning periods in 1991-92. Fawn recruitment was higher on treated areas during 1991 (P = 0.037) and 1992 (P = 0.069), with recruitment about twice as high on treated areas. In 1993, after 1 year of RIFA reinfestation, fawn recruitment did not differ between treated and untreated plots (P = 0.443). We conclude that high density RIFA infestations reduced white-tailed deer fawn recruitment.

A Metapopulation Approach to African Lion (Panthera leo) Conservation

Due to anthropogenic pressures, African lion (Panthera leo) populations in Kenya and Tanzania are increasingly limited to fragmented populations. Lions living on isolated habitat patches exist in a matrix of less-preferred habitat. A framework of habitat patches within a less-suitable matrix describes a metapopulation. Metapopulation analysis can provide insight into the dynamics of each population patch in reference to the system as a whole, and these analyses often guide conservation planning. We present the first metapopulation analysis of African lions. We use a spatially-realistic model to investigate how sex-biased dispersal abilities of lions affect patch occupancy and also examine whether human densities surrounding the remaining lion populations affect the metapopulation as a whole. Our results indicate that male lion dispersal ability strongly contributes to population connectivity while the lesser dispersal ability of females could be a limiting factor. When populations go extinct, recolonization will not occur if distances between patches exceed female dispersal ability or if females are not able to survive moving across the matrix. This has profound implications for the overall metapopulation; the female models showed an intrinsic extinction rate from five-fold to a hundred-fold higher than the male models. Patch isolation is a consideration for even the largest lion populations. As lion populations continue to decline and with local extinctions occurring, female dispersal ability and the proximity to the nearest lion population are serious considerations for the recolonization of individual populations and for broader conservation efforts.

Effects of supplemental prey, vegetation, and time on success of artificial nests

Despite intensive management on many grassland areas, nest loss to predators continues to result in low nest-survival rates. Management efforts are complicated by complex relationships among habitat, predators, and prey resources. We monitored the fates of artificial nests (908 in 1993, 827 in 1994) on Conservation Reserve Program (CRP) plots from April to July to test effects of prey supplementation, vegetation density, and time (month) on nest survival in agricultural and range landscapes in northwest Texas. Supplemental prey had the greatest effect on artificial nest survival and increased nest survival in both sparse and dense vegetation. Prey supplementation may be useful when used in conjunction with habitat management for dense nesting cover or in areas that already have dense vegetation. Nest survival was highest early in the nesting season, emphasizing the importance of available nesting cover during this period. Although least important, dense vegetation increased artificial nest survival. When evaluating management options, managers should consider logistical and economic costs of using supplemental prey, as well as potential effects on predator population dynamics.

Proximate Cues for a Short-Distance Migratory Species : an Application of Survival Analysis

Abstract Investigation of bird migration has often highlighted the importance of external factors in determining timing of migration. However, little distinction has been made between short- and long-distance migrants and between local and flight birds (passage migrants) in describing migration chronology. In addition, measures of food abundance as a proximate factor influencing timing of migration are lacking in studies of migration chronology. To address the relationship between environmental variables and timing of migration, we quantified the relative importance of proximate external factors on migration chronology of local American woodcock (Scolopax minor), a short distance migrant, using event-time analysis methods (survival analysis). We captured 1,094 woodcock local to our study sites in Michigan, Minnesota, and Wisconsin (USA) during autumn 2002–2004 and documented 786 departure dates for these birds. Photoperiod appeared to provide an initial proximate cue for timing of departure. Moon phase was important in modifying timing of departure, which may serve as a navigational aid in piloting and possibly orientation. Local synoptic weather variables also contributed to timing of departure by changing the rate of departure from our study sites. We found no evidence that food availability influenced timing of woodcock departure. Our results suggest that woodcock use a conservative photoperiod-controlled strategy with proximate modifiers for timing of migration rather than relying on abundance of their primary food, earthworms. Managing harvest pressure on local birds by adjusting season lengths may be an effective management tool with consistent migration patterns from year to year based on photoperiod.

Foraging location quality as a predictor of fidelity to a diurnal site for adult female American woodcock Scolopax minor

Abstract Quality of recently used foraging areas is likely an important predictor of fidelity to specific locations in the future. We monitored movement and habitat use of 58 adult female American woodcock Scolopax minor at three study areas in Minnesota, Wisconsin and Michigan, USA, during autumn 2002 and 2003, to assess the relationship between foraging habitat use decisions and environmental conditions at previously used foraging locations. We assessed whether habitat variables which related to food and weather were related to distance between locations on subsequent days of individual woodcock that choose diurnal foraging locations when they return from night-time roosting locations. We predicted that woodcock would return to foraging locations used on the previous day (i.e. shorter distances between daily foraging locations) when environmental conditions on the prior day were favourable. Woodcock generally made short (i.e. 48% < 50 m and 91% < 400 m) between-day movements, but also occasionally (∼ 7%) abandoned prior foraging areas. The primary determinants of woodcock movements during autumn (prior to migration) were low local food availability and potential for increased food availability elsewhere. The quality of foraging locations was an important predictor of future foraging habitat use for woodcock, consistent with the hypothesis that woodcock movement behaviour balances the risks associated with movement with the potential benefits of increased energy intake in new foraging areas.

POPULATION CHARACTERISTICS, SURVIVAL RATES, AND CAUSES OF MORTALITY OF STRIPED SKUNKS (MEPHITIS MEPHITIS) ON THE SOUTHERN HIGH PLAINS, TEXAS

Abstract We examined morphological characteristics, abundance, survival rates, and causes of mortality for striped skunks (Mephitis mephitis) in the Southern High Plains region of Texas during 1994 and 1995. We captured 69 male skunks 133 times and 35 female skunks 57 times on 4 12.8-km2 plots. Estimates of abundance on plots ranged from 0.10 to 0.71 skunks/km2. Annual survival rates were 0.40 in 1994 and 0.48 in 1995. Survival curves did not differ significantly between years. From the 26 recovered carcasses, 50% of skunks died from human-caused trauma. Shooting of skunks around occupied houses was the largest single cause of mortality.