Eric C. Hellgren

Resource Partitioning in Sympatric Populations of Collared Peccaries and Feral Hogs in Southern Texas

Species introduced into systems with ecologically similar species are predicted to compete or undergo niche compression to allow coexistence. We examined space, time, and diets of the realized niches of two suiforms, native collared peccaries ( Tayassu tajacu ) and introduced feral hogs ( Sus scrofd ), in sympatry in southern Texas in 1991–1992. Eleven females (six peccaries, five hogs) representing distinct herds were outfitted with radiotrans-mitters. Patterns of habitat use varied ( P < 0.001) between species, with peccaries selecting chaparral plant communities and hogs selecting mesquite ( Prosopis glandulosa ) communities. Overlap in use of habitat was greatest during winter and lowest in spring. Predominantly crepuscular patterns of activity were exhibited by both species, with lowest overlap in activity occurring during winter. Grass was dominant in fecal samples of hogs during autumn, winter, and summer, and forbs were dominant in feces of peccaries in all seasons. Overlap in diet was most apparent during spring (100%) and least apparent during autumn (36%). High seasonal overlap on one axis of niche space was balanced by low overlap on other axes. Different patterns of habitat and diet selection combined with similar activity patterns were consistent with differences in cranial anatomy, digestive function, and eco-physiology between hogs and peccaries. Conditions providing competitive advantage to peccaries are predicted to be dense scrub cover and presence of succulents, whereas hogs may be favored by presence of free water and more open brush-savanna habitats.

Variation in Reproductive Biology of Male Black Bears

We compared the reproductive biology of male black bears in two study areas at different latitudes (36 and 47°N) and with dissimilar population characteristics (hunted versus unhunted) to test two null hypotheses stemming from previous studies: 1) no regional variation exists in male reproductive rhythms; 2) social factors do not contribute to variation. Both hypotheses were rejected. Serum–testosterone profiles differed between the two areas, with a sharper peak associated with the May–July breeding season among bears in Minnesota. Bears in Virginia and North Carolina had a longer period of elevated serum testosterone, in apparent accordance with more prolonged breeding periods reported for southerly populations of black bear. In both areas, serum-testosterone concentrations and size of testicles decreased from the breeding months to autumn. By December, when all bears in Minnesota were denned, testicles had ascended into the body cavity, and serum testosterone reached a nadir. Serum testosterone increased during late denning (February–March), and testicles of some bears became scrotal, supporting previous suggestions that the male reproductive cycle is triggered by photoperiod. However, we also observed age–specific differences in secretion of testosterone between study sites that appeared to be related to the effects of differing social structures.

Population characteristics and winter ecology of black bears in Coahuila, Mexico

Biology, status, and distribution of black bears (Ursus americanus) in Mexico are poorly understood. We studied a population of black bears in the Serranias del Burro, Coahuila, Mexico, from 1991 to 1994 to address the hypothesis that the recolonization source for bears in Texas is the Sierra del Carmen range in northern Mexico. We also described aspects of winter ecology in this southerly population. We captured 42 bears (27 M, 15 F) and equipped 28 with radiotransmitters. All pregnant females (n = 13) and 2 of 5 females with yearlings denned, whereas all other bears, including 10 males, remained active during winter. Mean (± SE) den entry and exit dates for pregnant females (n = 5) were 25 December (± 5 days) and 22 April (± 2 days). Mean age at primiparity was 4.5 ± 0.6 years (n = 4), interbirth interval was 2.0 ± 0.0 years (n = 3), and litter size was 2.75 ± 0.25 cubs/female (n = 12). Estimated adult female and cub annual survival rates were 0.94 ± 0.05 and 0.81 ± 0.10, respectively, based on radiotelemetry and observation of family groups. Estimates of subadult male survival ranged from 0.88 ± 0.08 to 1.00 ± 0.00. We estimated density to be 0.35 bears/km 2 using a modification of the Lincoln-Petersen estimator that employs animal-equivalents. Because of high reproductive rates and lack of anthropogenic mortality, our data were consistent with the hypothesis that the area can serve as a source of bears emigrating to western Texas. Future bear research in this region should focus on determination of the source of emigrating bears, and identification and conservation of corridors linking Mexican and Texan populations of black bears.

Microhabitat selection by Texas horned lizards in southern Texas

The Texas horned lizard (Phrynosoma cornutum) has declined throughout its range. Understanding habitat selection by the Texas horned lizard is an important factor in its conservation. We examined daily and seasonal habitat requirements of Texas horned lizards and determined whether habitat selection differed among land management treatments in southern Texas. We used 5 study sites, each with a different burning and grazing treatment. Adult lizards caught in the study sites were fitted with backpacks carrying radiotransmitters and relocated daily. Habitat characteristics at radio locations and random points 10 m from the lizard were assessed using 50- × 20-cm quadrats. Relocations were made during 3 time intervals (morning, afternoon, evening) and 2 seasons (active, inactive). Horned lizards used bare ground and herbaceous vegetation similar to their availability in the morning and evening for thermoregulation and foraging purposes, but avoided bare ground in the afternoon. In the afternoons, lizards selected woody vegetation and litter as thermal refuges and cover from predators. Lizards also appeared less dependent on herbaceous vegetation and more dependent on woody vegetation and litter in the inactive season compared to the active season as a result of increased temperatures. We did not detect differences in habitat selection among land management treatments. Habitat management for Texas horned lizards should focus on creating a mosaic of bare ground, herbaceous vegetation, and woody vegetation in close proximity.

Demography of a collared peccary population in South Texas

Population dynamics of large herbivores in semiarid environments are regulated by rainfall. Reductions in reproduction and juvenile survival are the main mechanisms of regulation. We examined population characteristics of a harvested collared peccary (Tayassu tajacu) population in South Texas to model population responses to harvest. We sampled a peccary population from 1974 to 1993, intensively collecting data from 1989 through 1993. Mean (±SE) ovulation rate (2.13 ± 0.03, n = 181) and litter size (1.89 ± 0.03, n = 151) of adults did not vary by age class (P = 0.15) or year (P = 0.94), although litter sizes of yearlings (10-21 months old) (1.71 ± 0.19, n = 7) tended (P = 0.07) to be smaller than age-class 3 adults (5-7 yr old). Minimum age at predicted primiparity was 20 months. Pregnancy rate was positively associated (χ 2 = 6.20, P = 0.013) with rainfall in the previous year. Estimated fecundity (F young/F/yr) for yearlings and adults was 0.41 and 1.0, respectively. The sex ratio of harvested animals (53.3% M, n = 1,125, P = 0.027) was skewed toward males. Lack of age-specific variation (P = 0.23) in postnatal ratios suggested that harvest was not sex specific. Age structure varied (P = 0.08) among years, with fewer old animals in 1989-93 harvests. Male and female annual survival estimates were 0.90 ± 0.17 and 0.87 ± 0.05, respectively, from 1977 to 1983 telemetry data for unharvested herds, and did not differ (P = 0.88). From life table analyses of harvested herds from 1989 to 1993, male and female annual survival estimates were 0.65 ± 0.03 and 0.73 ± 0.04, respectively, and did not differ (P = 0.13). Year, age, and reproductive status affected (P < 0.05) condition indices, namely kidney fat, total mass, and eviscerated mass. Population modeling provided an estimated rate of juvenile (≤9 months) survival of 0.32 to maintain a stationary population under the 1993 harvest rate of 20%. We propose that juvenile survival is compensatory to adult mortality attributable to hunting. Relationships among juvenile survival, density, and forage resources need field investigation to explore the effect of density-dependent survival on dynamics of peccary populations

Spatial use and group dynamics of sympatric collared peccaries and feral hogs in Southern Texas

Range and group dynamics of collared peccaries ( Tayassu tajacu ) and feral hogs ( Sus scrofa ) on the Welder Wildlife Refuge near Sinton, Texas, were studied during June 1991– November 1992. Eleven females (six peccaries, five hogs) representing distinct herds were outfitted with radiotransmitters. Crude densities of peccaries and hogs were estimated at 2.0 and 9.5 animals/km2, respectively. Peccary herds were highly cohesive units, in contrast to hogs, which exhibited a flexible grouping pattern. Ecological density of peccaries appeared to be negatively related to the density of observations of hogs within individual territories of peccaries. The distribution of group sizes also differed for peccaries in areas of low abundance of hogs (two herds) and in areas of high abundance of hogs (four herds). Size of home ranges did not differ between species. Home ranges of both species were larger during summer than spring. Overlap occurred between ranges of peccaries and hogs, but was diminished at the level of 75 and 50% core areas. Peccaries have declined on the study area for nearly 30 years, and feral hogs may have been involved in reducing herd and group size of peccaries.

Status, Distribution, and Summer Food Habits of Black Bears in Big Bend National Park

The black bear (Ursus americanus), formerly widespread throughout Texas, is now restricted to the western portion of the state (Davis, 1974). In 1987, it was classified as an endangered species in Texas. Virtually all that is known about the present status and distribution of black bears in Texas is from isolated sightings, usually associated with forested or brushy habitat with a moderate to high cover density and diversity, rugged topography, and low human population densities (<4/km2, R. B. Taylor, in litt.) Monitoring has been suggested to locate suitable habitat where possible restoration and management efforts can be directed. Suitable habitat for black bears in Texas occurs

Serum and urine biochemical indicators of nutritional status in adult female collared peccaries, Tayassu tajacu (Tayassuidae)

Abstract 1. 1. Physiological responses of 13 adult female collared peccaries (Tayassu tajacu) to high quality and low quality diets, fed for 15 weeks, were examined. The low quality diet simulated energy and protein intake of peccaries during poor range conditions resulting from drought. Blood samples were collected after 10 and 15 weeks of dietary treatment; urine samples were collected after 15 weeks of treatment. 2. 2. Females receiving the low quality diet for 15 weeks lost 27.4% of their original body weight, compared to no weight change among high quality-fed females. 3. 3. Red blood cell counts, hematocrits, and hemoglobin concentrations were significantly greater among females fed a high quality diet compared to those receiving a low quality diet. High quality-fed females also had a higher mean corpuscular hemoglobin concentration. Plasma fibrinogen concentration was nearly twice as great among females receiving the low quality diet compared to the high quality group. 4. 4. Consumption of the low quality diet resulted in significantly elevated serum levels of nonesterified fatty acids, alkaline phosphatase, phosphorus, alpha-2 globulin and alpha globulin: beta globulin ratio. 5. 5. Consumption of the low quality diet resulted in significantly lowered serum levels of urea nitrogen, calcium, zinc, calcium: phosphorus, urea index, beta-1 flobulin, beta globulin: albumin ratio, thyroxine and triiodothyronine. 6. 6. Serum levels ofcreatinine, total bilirubin, glucose, cholesterol, gamma glutamyltransferase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, potassium, copper, magnesium, sodium chloride, total protein and gamma globulin were unaffected by diet quality. 7. 7. Urine chemistry results suggested pH, osmolarity, albumin, creatinine phosphokinase, calcium and phosphorus concentrations might be useful indices for assessing nutritional status in female peccaries.

Serum progesterone, estradiol-17β, and glucocorticoids in the collared peccary during gestation and lactation as influence by dietary protein and energy

Sixteen pregnant collared peccaries were assigned to four experimental diets representing two levels of crude protein and two levels of digestible energy. Serum levels of progesterone, estradiol-17 beta (E2), and glucocorticoids were measured by radioimmunoassay. There was no significant dietary effect (P greater than 0.05) associated with any hormone during gestation. Progesterone did not differ between days 11 and 140 of gestation (X +/- SE = 36.48 +/- 1.11 ng/ml, N = 72), began to decline during the last week prepartum, and continued to decline within 24 hr of birth. Glucocorticoid concentrations remained level throughout gestation (X +/- SE = 6.57 +/- 0.45 microgram/dl, N = 74). E2 levels were low during the first 90 days of gestation, rose significantly (P less than 0.001) from 10.11 +/- 1.73 pg/ml (X +/- SE, N = 8) at Days 81-90 gestation to 49.07 +/- 12.87 pg/ml (N = 3) at 2-4 days prepartum (Days 141-147 of gestation), and declined rapidly to baseline levels within 24 hr of farrowing. Litter size had no effect on progesterone or E2 concentrations. There was no significant dietary effect on litter size or gestation length. During lactation, glucocorticoids and E2 remained stable and did not differ by diet, while progesterone concentrations appeared to be affected by diet. Individuals on the high energy-high protein diet returned to normal ovarian function before animals on the other three diets. Results indicated that the pregnant collared peccary can maintain a reproductive steroid environment that allows for fetal development in the face of moderate caloric or protein restriction and that the lactating peccary can undergo a postpartum ovulation in the presence of good nutrition.

Physiological responses of the adult male collared peccary, Tayassu tajacu (tayassuidae), to severe dietary restriction

Metabolic and hormonal responses of eight adult male collared peccaries (Tayassu tajacu) to an ad libitum diet intake, or 25% of an ad libitum intake, were examined. Blood samples for hematological, serum-biochemical and hormonal profiles were collected at three week intervals during the nine week experiment starting 4 August 1983. Males fed on the restricted diet lost an average of 26% of their body weight during the trial, compared to a slight weight gain for those fed ad libitum. Characteristics of the red and white blood cell populations were not influenced by diet intake, with the exception of mean corpuscular volume, which was consistently lower amongst males fed on the restricted diet. Restricted food intake resulted in significantly elevated serum values for urea nitrogen, urea nitrogen:creatinine, urea index, alpha globulin:beta globulin, gamma globulin:albumin, nonesterified fatty acids, alkaline phosphatase and lactate dehydrogenase isozymes (LD1 and LD2). Restricted food intake resulted in significantly lowered serum values for total alpha globulin, alpha-1 globulin, total beta globulin, beta-1 globulin, beta-2 globulin, glucose, triglycerides, calcium, magnesium, sodium, chloride, copper and triiodothyronine. Serum levels of creatinine, total protein, albumin, alpha-2 globulin, uric acid, total bilirubin, cholesterol, aspartate aminotransferase, alanine aminotransferase, gamma glutamyltransferase, lactate dehydrogenase, phosphorus, calcium:phosphorus, potassium, iron, zinc and thyroxine were unaffected by diet intake level. Semen evaluation indicated spermatogenesis was not affected by dietary restriction despite reductions in scrotal circumference and ejaculate gel volume. Serum testosterone levels were significantly lower among males fed on the restricted diet after nine weeks. These data suggest male libido might be depressed during poor range conditions, while maintenance of spermatogenesis might permit them to take immediate advantage of improved range conditions. Blood analysis of metabolic and hormonal function can provide useful information for predicting the adult males nutritional and reproductive condition.