Stephen Demarais

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.

Home range of Desert Mule Deer : Testing the body-size and habitat-productivity hypotheses

The body-size hypothesis of home range predicts that, given constant home range productivity, larger animals with higher absolute metabolic requirements use larger home ranges to meet their metabolic needs. This relationship is well supported across a wide range of mammals and often has been invoked to explain differences in home range size between sexes that differ in body size However, the body-size hypothesis has rarely been tested within a species A corollary to this hypothesis states that for a given mass, animals in areas of low habitat productivity should have home ranges larger than those in productive habitat. To test these 2 hypotheses, we radiomonitored desert male deer (Odocoileus hemionus crooki) for 2 vears insouthwest Texas to determine the effects of sex, mass, and habitat productivity on annual home range size, Although male mule deer had more massive bodies than females (P < 0.001) and used consistently larger annual home ranges than females (P < 0.01), we found little support for the body-size hypothesis. In contrast, we found sex-specific support for the habitat-productivity hypothesis. Male and female mule deer had home ranges of similar size in areas of high habitat productivity but males used larger home ranges than females when habitat productivity was low, Our results suggest that differential sex responses to productivity may be the mechanism underlying the frequent observation that male cervids have larger home ranges than female cervids.

Genetic consequences of white-tailed deer (Odocoileus virginianus) restoration in Mississippi.

White‐tailed deer (Odocoileus virginianus) were nearly extirpated from the southeastern USA during the late 19th and early 20th centuries. Recovery programmes, including protection of remnant native stocks and transplants from other parts of the species’ range, were initiated in the early 1900s. The recovery programmes were highly successful and deer are presently numerous and continuously distributed throughout the southeastern USA. However, the impact of the recovery programmes on the present genetic structure of white‐tailed deer remains to be thoroughly investigated. We used 17 microsatellite DNA loci to assess genetic differentiation and diversity for 543 white‐tailed deer representing 16 populations in Mississippi and three extra‐state reference populations. There was significant genetic differentiation among all populations and the majority of genetic variation (≥ 93%) was contained within populations. Patterns of genetic structure, genetic similarity and isolation by distance within Mississippi were not concordant with geographical proximity of populations or subspecies delineations. We detected evidence of past genetic bottlenecks in nine of the 19 populations examined. However, despite experiencing genetic bottlenecks or founder events, allelic diversity and heterozygosity were uniformly high in all populations. These exceeded reported values for other cervid species that experienced similar population declines within the past century. The recovery programme was successful in that deer were restored to their former range while maintaining high and uniform genetic variability. Our results seem to confirm the importance of rapid population expansion and habitat continuity in retaining genetic variation in restored populations. However, the use of diverse transplant stocks and the varied demographic histories of populations resulted in fine‐scale genetic structuring.

Age and regional differences in antlers and mass of white-tailed deer

Quantifying how physiographic region affects age-related physical development of white-tailed deer (Odocoileus virginianus) will aid in understanding land management and harvest regulation impacts. We analyzed 1991-98 harvest data from Mississippis Deer Management Assistance Program (DMAP) and wildlife management areas consisting of 247,051 deer from 5 physiographic regions in Mississippi. Sex, age, and region affected eviscerated body mass (P < 0.001). Age and region affected an antler size index (P < 0.001). However, significant interactions between age and regions and differences in the slopes of growth rates for body mass and an antler size index indicated these variables develop differently across the physiographic regions for each sex. Managers should use caution when grouping body mass samples for 2.5-, 3.5-, and ≥4.5-year-old deer, as changes in age composition with limited sample size could bias mass results. Soil fertility should be considered when designing age-based selective harvest programs when management goals include maximizing antler size at harvest.

Northern bobwhite chick mortality caused by red imported fire ants

Northern bobwhite (Colinus virginianus) populations have declined throughout their range during the last 30 years. Change in land management is thought to be a primary cause of this decline, but the invasion of northern bobwhite habitats by the red imported fire ant (Solenopsis invicta) also may be involved. We compared hatching success and subsequent survival of wild northern bobwhite chicks on the Coastal Prairie of Texas in 1997 and 1998 between broods that hatched under natural conditions or following fire ant suppression treatments. In 1997, the fire ant suppression treatment resulted in a 70% reduction in the number of red imported fire ants on baits placed in treated nests on the day after hatch. Using 2 fire ant suppression treatments in 1998 reduced the number of red imported fire ants on baits by >99%. No year or treatment × year interaction effects were detected for hatching success or survival, and no treatment effect was detected for hatching success (P > 0.10). However, the proportion of chicks surviving to 21 days was higher (P = 0.010) for treated nests (n = 18) than control nests (n = 25; proportions of broods surviving: 53.5 8.6% [x SE] vs. 24.7 ± 6.6%; chick survival: 60.1 ± 7.6% vs. 22.0 ± 6.2%). The probability of chick survival decreased (P < 0.001) as our index of red imported fire ant activity in the nest increased. These results indicate northern bobwhite chicks can suffer high levels of mortality due to red imported fire ants, which could explain declines in some northern bobwhite populations following infestations by red imported fire ants. Current methods for controlling red imported fire ants are expensive and may last <3 months. Thus, strategies for mitigating the effect of red imported fire ants to northern bobwhite populations in this area should probably focus on reducing other mortality factors or increasing productivity.

MULTIPLE PATERNITY IN WHITE-TAILED DEER ( ODOCOILEUS VIRGINIANUS) REVEALED BY DNA MICROSATELLITES

Abstract Multiple paternity in single litters (siring of offspring by >1 male) has been documented in several taxa with different mating systems. However, information on occurrence of multiple paternity in ungulates is lacking. We used 19 DNA microsatellite markers to assign parentage in 41 litters of captive white-tailed deer (Odocoileus virginianus) born in 6 pens with multiple males during 1997–1999. We detected multiple paternity in 7 of 27 litters with ≥2 offspring, occurring in 4 of 6 pens: 2 of 3 triplet litters and 5 of 24 twin litters. This is the first reported evidence of multiple paternity for single ungulate litters, which indicates that some aspects of ungulate reproductive ecology are not well understood. The occurrence of multiple paternity in litters of free-ranging ungulates would have implications for ungulate mating systems and reproductive strategies. Sex-linked microsatellite markers may provide a promising method for investigating female promiscuity in free-ranging ungulate populations where litter size is typically ≤2 offspring.

Spatial Scale Dependence of Rodent Habitat Use

Many insights into community ecology over the past 3 decades were derived from investigations of associations of rodent species with microhabitats. Nonetheless, studies of microhabitat use of rodents are inconsistent, suggesting spatially dependent interacting factors. We investigated the relative ability of microhabitat and macrohabitat to predict rodent captures in traps placed in 48 trapping grids of 90 traps each during spring and autumn of 1993 and 1994 (17,280 data points). Trapping grids represented eight replications of six discrete macrohabitats. We used discriminant function analysis and random null models to compare the ability of microhabitat and macrohabitat to predict use of individual traps by 13 rodent species. Classification rates for presence at a trap by dummy variables of macrohabitats exceeded those obtained with principle components of microhabitats for nine of 13 species. In seven of those cases, classification rate exceeded that expected from a random distribution of dummy variables. Of the four cases where principle components of microhabitats out-classified dummy variables of macrohabitats, only two exceeded rates expected from a random distribution of dummy variables. Thus, microhabitat partitioning for many species is constrained by local macrohabitat conditions.

Measuring Fine-Scale White-Tailed Deer Movements and Environmental Influences Using GPS Collars

Few studies have documented fine-scale movements of ungulate species, including white-tailed deer (Odocoileus virginianus), despite the advent of global positioning system (GPS) technology incorporated into tracking devices. We collected fine-scale temporal location estimates (i.e., 15 min/relocation attempt) from 17 female and 15 male white-tailed deer over 7 years and 3 seasons in Oklahoma, USA. Our objectives were to document fine-scale movements of females and males and determine effects of reproductive phase, moon phase, and short-term weather patterns on movements. Female and male movements were primarily crepuscular. Male total daily movements were 20% greater during rut (7,363m±364) than postrut (6,156m±260). Female daily movements were greatest during postparturition (3,357m±91), followed by parturition (2,902m±107), and preparturition (2,682m±121). We found moon phase had no effect on daily, nocturnal, and diurnal deer movements and fine-scale temporal weather conditions had an inconsistent influence on deer movement patterns within season. Our data suggest that hourly and daily variation in weather events have minimal impact on movements of white-tailed deer in southern latitudes. Instead, routine crepuscular movements, presumed to maximize thermoregulation and minimize predation risk, appear to be the most important factors influencing movements.

Using Fractal Analyses to Characterize Movement Paths of White-Tailed Deer and Response to Spatial Scale

Abstract It is often difficult to test hypotheses about how and why animal movement responds to environmental conditions, and at what spatial scales movement decisions are made, all of which are critical for sound management. We used fractal dimension (D) as a measure of tortuosity because it described animal movement patterns and was useful for testing hypotheses about effects of sex, home-range size, monthly rainfall, and reproductive phase on movement paths and for detecting changes in movement patterns of animals across a range of movement distances. We captured and fitted 33 (18 females and 15 males) white-tailed deer (Odocoileus virginianus) with global positioning system collars. We found that females moved more tortuously (D  =  1.75 ± 0.035 SE) than males (D  =  1.549 ± 0.025). These differences in movement were related to home-range size of females but not of males. Rainfall predicted D for females; thus, females may have been able to forage more intensively in a smaller area due to increased forage availability. Fractal D of females was greatest during the parturition period (1.468 ± 0.02), likely due to restricted movements in smaller areas or increased foraging. Home-range size of males was similar in spring and rut, but D was lower during rut, indicating that deer changed movement patterns within previously established home ranges. Movement patterns were similar at path lengths related to foraging patches and home ranges, whereas movement patterns changed as path length approximated the size of habitat patches.

DESERT MULE DEER SURVIVAL IN SOUTHWEST TEXAS

Abstract We studied population structure and limiting factors within a desert mule deer (Odocoileus hemionus eremicus) population in Brewster County of the Trans-Pecos Region in Texas, USA. We estimated and compared annual survival and pregnancy rates from March 1990–February 1993 for 121 adult (>33 months old) male and female, 61 subadult (21–33 months old), and 77 young (8–20 months old) deer. Variation in weather patterns (i.e., drought) was associated with—if not causative of—annual variation in survival patterns. Adult female and young survival had the strongest correlation with drought. Pregnancy status of young (≤1.5 yr) and old (≥6.5 yr) deer appeared most affected by drought. Seasonal periods of natural stress differed for adult sex classes, with most female mortalities occurring during months associated with parturition and lactation, and most male natural stress losses occurring during late winter and early spring. The major mortality sources were hunting and natural stressors for adult males, natural stressors and predation for adult females, and predation and natural stressors for young. Subadult mortalities were too few to identify significant mortality agents. The significance of natural stress-related survival and fecundity impacting herd productivity and stability warrants further consideration of poorly understood causative mechanisms. Ideally, replicated treatment areas would be used to address compensatory and additive mortality issues relative to predator abundance, harvest, and natural-stress losses.