Lucina Hernández

Foraging in the ‘landscape of fear’ and its implications for habitat use and diet quality of elk Cervus elaphus and bison Bison bison

Abstract In 1995, wolves Canis lupus were reintroduced into Yellowstone National Park, USA, where they began to prey on ungulate species. In response to this new predation risk by wolves, we predicted that the two main ungulate species, elk Cervus elaphus and bison Bison bison, should compensate by reducing their use of riskier open meadows and increasing their use of safer forest. Additionally we predicted that this shift in habitat use would result in reduced diet quality. We tested the first prediction by regressing the number of faecal groups in 10-m2 sampling plots against distance from forest edges. To test the second prediction, we compared percent faecal nitrogen in elk and bison faeces between areas with and without wolves. We found a significant negative relationship between number of elk faecal groups and distance from forest edge in areas with wolves (r2 = 0.65, P = 0.001), but we did not find a relationship between these two factors in areas without wolves. Mean percent faecal nitrogen in elk was significantly lower (F(1,116) = 13.9, P < 0.001) in areas with wolves (1.7%, SE = 0.09, N = 40) than in wolf-free areas (2.1%, SE = 0.08, N = 80). For bison, we did not find any significant relationship between numbers of faeces and distance from forest edge nor in dietary nitrogen between wolf and wolf-free areas. We concluded that predation pressure from the reintroduced wolves was consistent with our prediction that elk shifted habitat use, thus lowering the quality of their diet. However, a similar change in use pattern and dietary quality of bison in response to wolf presence was not found.

Winter hunting habitat of pumas Puma concolor in northwestern Utah and southern Idaho, USA

Pumas Puma concolor are stalking predators of large ungulates that usually cache their prey. We hypothesize that they require specific habitats to successfully stalk their prey and that they select cache sites based on some set of criteria. We tested these predictions during a study of predation by pumas on mule deer Odocoileus hemionus in south-central Idaho and northwestern Utah, USA. We found cache points of puma-killed deer in winter by locating radio-collared pumas. We then located where pumas had killed deer (kill points) by tracks in the snow. We classified these kill points relative to the dominant forest type and association with open, edge or forested areas. At a subset of the kill points and associated cache points, we also estimated tree and shrub density, tree diameter at breast height (dbh), shrub height and slope. Pumas killed deer more often than expected (P < 0.001) in juniper-pinyon habitat and in edge areas. Tree densities and dbh at cache points were significantly greater (P < 0.001) than at kill points or surrounding areas. We concluded that pumas relied on specific habitat characteristics to kill mule deer, and selected cache sites with older, larger trees.

Numerical and Demographic Responses of Pumas to Changes in Prey Abundance: Testing Current Predictions

Abstract Information on factors affecting population size of pumas (Puma concolor) can be important because their principal prey over most of the western United States are valued big game species (e.g., mule deer [Odocoileus hemionus], elk [Cervus elaphus], and bighorn sheep [Ovis canadensis]). Based on the hypothesis that puma numbers are limited by their food supply, puma populations should track changes in prey abundance by growing exponentially with increases in prey and by declining with a lag response when prey decreases. Additional predictions proposed by researchers are that body mass of pumas, female productivity, kitten survival, and adult survival should decrease after a prey decline. We used a 15-year database from a hunted population of pumas in southern Idaho and northwestern Utah to test these predictions. During the 15-year time span of the database, a major decline in mule deer abundance occurred. Estimates of puma numbers and demographic characteristics came from intensive capture and radiocollaring efforts. We calculated kitten and adult survival with MICROMORT software. We found that adult puma numbers increased exponentially at r = 0.07 during a period of increasing mule deer numbers. Four years after the mule deer abundance declined, puma numbers decreased at a rate of r = −0.06. Body mass of female pumas was lower after the decline in puma numbers (42.6 ± SE = 1.2 kg, n = 40 vs. 40.1 ± 0.64 kg, n = 34, t = 5.06, P = 0.045). Kitten survival was less after the decline in deer abundance (0.573 ± 0.016, n = 30 vs. 0.856 ± 0.015, n = 25, Z = 2.40, P < 0.01). Survival of resident females was significantly less after the decline in puma numbers (0.783 ± 0.03 vs. 0.929 ± 0.019, U = 55.0, P = 0.009). Female productivity did not differ before or after the decline in deer abundance. Our results supported the majority of the predictions concerning the impact of changing deer abundance, which supported the hypothesis that the abundance of mule deer limited our population of pumas.

Growth curve models and age estimation of young cougars in the northern great basin

We analyzed mass growth of 96 cougars (Puma concolor) from south-central Idaho and northwestern Utah with a Richards growth curve, tested the applicability of the curve for total body length and tail length, and tested whether changes in mass, total length, and tail length could be used to predict ages of young animals. The Richards curve provided good fits of the data for mass (M: R 2 = 0.986; F: R 2 = 0.966), total length (M: R 2 = 0.961; F: R 2 = 0.958), and tail length (M: R 2 = 0.949; F: R 2 = 0.948). The mass growth model analysis indicated differences in sex for adult mass, growth rate, and birth weight. The growth model for total length indicated a sex effect for adult total length. The model for tail length was free of any sex effects. Separate simple linear regressions of the log e (age) to the log e (mass), log e (total), and log e (tail length) provided good fits of the data for males and females (r 2 mass = 0.957 and 0.938, r 2 total length = 0.939 and 0.968, and r 2 tail length = 0.918 and 0.955, respectively). We propose that models based on body mass, total length, and tail length are useful in studying the biology and ecology of cougar populations and developing sound management policies for this species.

From the Field Use of camera traps to measure predation risk in a puma-mule deer system

Abstract Previous work indicated that automated camera traps may be useful in estimating predation risk among different microhabitats for mule deer (Odocoileus hemionus). We tested the prediction that the number of photographs taken by automated camera traps was inversely related to the amount of food left by deer in feeding boxes or giving up densities (GUDs). We positioned camera traps adjacent to standard mule deer feeding boxes placed in open and edge microhabitats of 3 forest types: Douglasfir (Pseudotsuga menziesii), juniper (Juniperus osteosperma), and mountain mahongany (Cercocarpus ledifolius). We compared number of photographs taken with daily GUDs for the boxes for the 2 microhabitats. We found that GUD data of our study coincided with the previous work of lower GUDs in open versus edge microhabitats for Douglas-fir (288.6±17.1 g vs. 389.6±19.4 g; P<0.001) and juniper (218.9±26.3 g vs. 251.9±29.6 g, P=0.027) but not for mountain mahogany (272.4±29.5 g vs. 287.0±32.3 g, P=0.414). We also found significantly more total photos/camera taken in open microhabitat versus edge microhabitat in Douglas-fir (16.2±2.2 vs. 7.4±1.5; P=0.004). More photos/camera were taken in the open versus edge in the juniper forest type (15.6±3.9 vs. 11.5±3.9), but the difference was not significant. There was no difference in photos/camera between the 2 microhabitats in the mountain mahogany (18.4 ± 3.4 vs. 19.3 ± 1.9). Total number of photos/day/box also was significantly related to the GUDs for the 3 forest types (P = 0.002–0.008). The amount of variability explained by regression equations (r2adjusted) ranged from 22% for Douglas-fir to 29% for juniper. We concluded that the total number of photographs taken does reflect the results of GUD analysis and that automated camera traps could be used to assess predation risk among different microhabitats.

Foraging in the Landscape of Fear, the Predator's Dilemma: Where Should I Hunt?

Under predation risk, prey species are more abundant in areas of low predation risk even at the expense of forage quality. As a result two predictions are possible, 1) predators should choose to hunt in areas with fewer but easier to catch prey than areas where they are more abundant but harder to catch; and 2) the frequency of prey species in the diet of predators using low risk areas should be greater than, or at least equal to, the diet of predators using high risk areas. To test these two predictions, we used data on coyote Canis latrans abundance and diet composition from two habitats in the Chihuahuan Desert of Mexico that have different abundances of jackrabbits (Lepus californicus) and rodents. We used the number of coyote scats found in transects in the two areas to assess coyote abundance and analyzed the contents of these scats to determine diet composition. We found significantly more coyote scats/yr (22.6 ± 4.7 (SE) vs. 12.2 ± 2.4 scats/yr, d.f. = 7, paired t = 3.80, P = 0.007) in the habitat with less jackrabbits and more rodents. However, the percent occurrence of jackrabbits (54.3 ± 6.7% vs. 60.1 ± 7.7%) and rodents (32.6 ± 6.5% vs. 30.1 ± 6.0%) in coyote scats did not differ between the two habitats. These results supported both the above cited predictions and the hypothesis that prey vulnerability can influence habitat use by coyotes.

Do Female Pumas (Puma concolor) Exhibit a Birth Pulse

Abstract Female pumas (Puma concolor) give birth in all months of the year with a possible birth pulse in July–September. This pulse is proposed to be timed to provide increased survival probabilities to young born during these months. We tested data on birth dates from 8 different studies for a birth pulse. We also compared survival rates for young born in July–September to those for young born outside of these dates during a 17-year study in Idaho and Utah. The distribution of litters born per month was not uniform, with 41% of births occurring in July–September. Survival rates of young born in July–September were equal to those in other months of the year (0.774 ± 0.006 versus 0.779 ± 0.004). We conclude that there was a propensity for higher numbers of litters to be born in July–September. However, we rejected the hypothesis that young born in July–September had greater survival than young born at other times of the year. We suggest that rather than there being a survival advantage to pumas born in July–September, perhaps there is a survival disadvantage to those born in January–February (4.5% of 484 litters). However, there were insufficient data to test this alternate hypothesis.

REPRODUCTION OF BLACK-TAILED JACKRABBITS (LAGOMORPHA: LEPUS CALIFORNICUS) IN RELATION TO ENVIRONMENTAL FACTORS IN THE CHIHUAHUAN DESERT, MEXICO

Abstract Climatic elements can influence reproduction of mammals. In temperate zones, reproduction often is related to favorable environmental factors, such as spring and rainy seasons, which correspond to availability of food. The goal of this study was to describe the reproductive cycle of the black-tailed jackrabbit, Lepus californicus, with regards to temperature, rainfall, evaporation, and photoperiod in the Mapimí Biosphere Reserve in the central Chihuahuan Desert, Durango, Mexico. If the onset of breeding correlates with these environmental factors, we predicted that mating should be related to total rainfall. To test this prediction, we collected 39 females and 36 males between July 1996 and November 1997 and measured and recorded reproductive condition. Weights of ovaries in females were correlated with increases in photoperiod, evaporation, rainfall, and mean monthly temperature. Increases in male testicular weight were correlated with increasing photoperiod only. We concluded that differences in responses of males and females were related to differing reproductive strategies. Females experience higher reproductive costs and probably respond to a more complex set of environmental cues to increase their reproductive success.

Bottom-up regulation of desert grassland and shrubland rodent communities: implications of species-specific reproductive potentials

Abstract We conducted an 11-year comparative study on temporal variation in rodent density, biomass, and species composition dynamics from adjacent grassland and shrubland environments in the Chihuahuan Desert of North America, in relation to rainfall and plant production. We found that rodent assemblages from those environments were only 14% similar in overall species composition, but consisted of different species in the same genera with similar ecological attributes. Each rodent community was numerically dominated by a different species of granivorous kangaroo rat, and the 2 rodent communities paralleled each other in body sizes and trophic structure. Rodent species compositions changed little over the 11-year period, despite considerable variation in rodent densities and biomass and in rainfall and plant production. Rodent abundance and biomass from both communities increased in relation to temporally variable rainfall and plant production, especially resulting from a series of El Niño and La Niña Southern Oscillation events. However, the grassland rodent community exhibited more rapid within-1-year lag-time responses to plant production, and prolonged high densities for 1 year before declining, whereas the shrubland rodent community exhibited primarily 1-year lag responses and immediate rapid decline in densities. Changes in rodent densities and biomass from both communities were significantly predicted by the production of annual grasses and forbs. Measured rodent reproductive activity was greater and happened sooner after rain and plant production events at the grass site than at the shrub site, and differences in the timing of rodent bottom-up responses between the grassland and shrubland habitats appeared to result from differences in the reproductive potentials of the 2 dominant rodent species. Dipodomys ordii, the dominant grassland rodent species, is known to produce more offspring than Dipodomys merriami, the dominant rodent in the shrubland community. We conclude that differences in the reproductive potentials of these 2 dominant rodent species likely accounted for the quicker and prolonged response of the grassland rodent community to bottom-up influences, rather than differences in the timing of plant production between the sites. Variation in reproductive potentials among rodent communities is likely a key factor affecting the timing of overall rodent community dynamics relative to changes in environmental resources.

Home Range Size and Activity Patterns of Bobcats (Lynx rufus) in the Southern Part of their Range in the Chihuahuan Desert, Mexico

Abstract Home range size, daily travel distances, and diel activity patterns are important characteristics of how an animal uses its home range area. In species, such as the bobcat (Lynx rufus), with large geographical ranges, it is necessary to gather data on diverse populations across the range to better understand what might be factors influencing these home range parameters. Although there are many studies of bobcats in more northern areas of its range in the United States, few data exist from its extensive southern range in Mexico. To fill this gap in information, we collected data on home range size, daily travel distances, and diel activity patterns of bobcats from the center of the Chihuahuan Desert in Mexico. We compared our findings with available data from more northern studies and tested for any latitudinal trends in home range size. We trapped eight adult bobcats (four females and four males) between 2006 and 2008 at the Mapimi Biosphere Reserve in the Chihuahuan Desert. Each bobcat was equipped with a GPS radio collar that estimated their location and ambient temperature every half hour at night (1900 to 800 h), and every hour during the day (800 to 1900 h). These data were used to estimate total daily distance traveled, average speed, home range size, activity pattern, and to test for an association between hourly travel and ambient temperature. For bobcats in Mapimi, mean distances traveled daily (4.9 ± 0.7 km), mean speed (0.3 ± 0.4 km/h) and average home range size (25.9 km2 ± 3.7) did not differ from other places in U.S. (distance traveled daily 5.7 ± 1.4 km, mean speed 0.4 ± 0.4 km/h and home range size 34.0 ± 5.4 km2). Bobcats are most active from 1700 to 2300 h and from 0500 to 1200 h and showed a minimum activity period from 1300 to 1600 h. These patterns did not differ from what other studies found. Distance traveled was inversely correlated with environmental temperature (r2  =  0.506, P < 0.05). Our data demonstrate that most behaviors of bobcats in this hot desert environment did not differ in general from their more northern populations. Although our home range estimates were similar to other studies, our analysis did support a latitudinal decreasing trend that indicates factors other than those related to latitude are affecting home range size in bobcats. We suggest investigating other independent factors not related with latitude such as primary production and rainfall might help identify which, if any, of these factors contribute to home range size in bobcats.