Diego F. Castillo

Interindividual interactions of Molina's hog-nosed skunks Conepatus chinga in the Pampas grassland of Argentina

During one year, we radiotracked two female and two male Molina’s hog-nosed skunksConepatus chinga (Molina, 1782), a little studied mephitid, in the Pampas of central Argentina, to analyze the static and dynamic interactions between individuals. Mean home range overlap was large (44.5%), but males shared a smaller proportion of their home ranges than females. The average percentage of localizations in the overlap area (39.3%) indicates that these areas were not marginal sections of individual home ranges, but this value was greater for individuals of different genders than intrasexual dyads. The Coefficient of Spatial Association confirmed that the distances between individuals of different sexes were smaller than between animals of the same sex. During simultaneous locations, females were closer than males, but reciprocal distances between individuals varied over the time. These patterns are congruent with those described as typical for mustelids and mephitids. Our results confirm that an analysis of home range overlap should not be considered complete without the study of dynamic interactions among individuals and their temporal variations, which are necessary to overcome the limitations of spatial overlap analysis.

Field Immobilization of Molina’s Hog-nosed Skunk (Conepatus chinga) Using Ketamine and Xylazine

We injected 27 adult Molina’s hognosed skunks (Conepatus chinga) intramuscularly by hand with ketamine hydrochloride (KH) and xylazine hydrochloride (XH) in the Pampas grassland of Argentina. Skunks were immobilized with a mean (±SD) dosage of 24.9±6.5 mg/kg KH and 1.9±0.6 mg/kg XH. The mean effective dosages of KH (27.6 mg/kg) and XH (1.7 mg/kg) were higher and lower, respectively, than those reported in skunks previously. Mean induction and recovery time were 5.3±1.9 min and 47.7±18.5 min, respectively. Hypothermia was the only problem detected in field immobilization and occurred in winter but did not appear to be associated with to drug doses. We conclude that KH/XH is a safe immobilizing drug combination for Molina’s hog-nosed skunk.

Feeding habits of Molina’s hog-nosed skunk in the Pampas grassland of Argentina

Abstract We studied the feeding ecology of Molina’s hog-nosed skunk (Conepatus chinga) in a protected area of the Pampas grassland by comparing the content of scats (140 samples) to prey abundance (estimated by invertebrate capture rates from 38 pitfall trap grids). Fecal analysis supported a largely insectivorous diet, with small vertebrates and carrion representing minor alternative resources. Almost all invertebrate prey was significantly more abundant in the warm period than the cold period, whereas skunk diet did not vary seasonally. Even though Molina’s hog-nosed skunks were considered to be opportunistic foragers due to their wide trophic niche, our results indicate that despite their trophic generalism, they consumed several prey items in proportions differing from those expected by their respective availabilities.

Home range size and habitat selection of Geoffroy’s cat (Leopardus geoffroyi, Felidae, Carnivora) in the pampas grassland

Abstract This study examined the spatial ecology of Geoffroy’s cats, Leopardus geoffroyi, living in a protected area surrounded by croplands in the Argentine grasslands. A total of six different adults were marked with 14 radio-collars from 2001 to 2005 but only three (one female and two males) produced a meaningful amount of data (54–135 positions). Total home range size was 8.83±1.58 km2 (100% Minimum Convex Polygon) and 7.27±2.23 km2 (90% Fixed Kernel). Core areas averaged 1.46±0.84 km2. Geoffroy’s cats most frequently used Exotic Woodland areas followed by Rocky and Agricultural areas. All cats clearly avoided natural habitats and selected Exotic Woodland at the two levels of selection examined: within the study area and within home ranges. In our study area, Geoffroy’s cats’ home ranges were larger than all those previously recorded in natural areas. The Geoffroy’s cat preference for Exotic Wood patches and avoidance of natural grasslands was likely due to the degradation of natural habitats caused by a dense population of feral horses. We also argue that woodlands can play an important role in the ecology of this species, either as refuge, hunting area or for territorial marking, regardless of their origin.

Habitat selection of Molina's hog-nosed skunks in relation to prey abundance in the Pampas grassland of Argentina

Abstract We radiotracked 16 (6 males, 10 females) adult Molinas hog-nosed skunks (Conepatus chinga) to examine habitat selection using compositional analysis at 2 spatial scales in a protected area and a landscape fragmented by agriculture. To aid in understanding the habitat use of skunks, the abundance of invertebrates was estimated in each habitat. Habitat use and selection varied between the 2 study sites. Skunks selected habitat at landscape level but not at home range level in the protected area. In the cropland area skunks showed overall habitat selection at both scales, although at landscape level we did not detect a significant ranking of habitats. In both sites, when we found a significant selection grassland patches ranked first. Although this habitat does not reach 10% of the total area, it presented the highest abundance of Coleoptera. Because Coleoptera are the main prey item of this mephitid, these results support the hypothesis that habitat selection in C. chinga is highly related to food availability. We conclude that the preservation of grassland patches may be essential for managing C. chinga populations in the highly human-modified landscapes of the Pampas.

Diet of Adults and Cubs of Lycalopex gymnocercus in Pampas Grassland: A Validation of the Optimal Foraging Theory?

We compared the diet of adult Pampas foxes (Lycalopex gymnocercus) and their cubs in a Pampas grassland area of Argentina by analysing 152 scats (adults: 92, cubs: 60). We used an Index of Relative Importance (IRI) to determine the contribution of prey items to the diet. IRI scores for rodents, hares and birds were higher for cubs, whereas adults consumed grasshoppers and larvae more often than cubs did. Fruits and carrion of ungulates were consumed only by adults. Both the number of items per scat and diet diversity were smaller for cubs than adults. We conclude that the Pampas fox behaves as a typical central place forager, with fruits and insects being probably consumed on the spot (with low foraging costs) and rodents, birds and hares being brought to the den for the cubs.

Chemical immobilisation of free-ranging Pampas foxes (Pseudalopex gymnocercus): Assessment of ketamine–xylazine and tiletamine–zolazepam combinations

Two protocols to immobilise free-ranging Pampas foxes for ear-tagging or radio-collaring were evaluated. One hundred fifteen foxes were injected with ketamine-xylazine (K-X) and thirteen with tiletamine-zolazepam (T-Z). The use of both T-Z and K-X combinations typically resulted in a smooth induction and recovery. In 86% of the cases K-X protocol was judged effective (mean±SD, K: 10.7±3.3mg/kg, X: 1.0±1.0mg/kg) while T-Z protocol was judged effective in 92% of the cases (T: 3.6±1.05mg/kg, Z: 3.6±1.05mg/kg). The primary differences between the two drug combinations were that the time necessary for the complete recovery was longer with T-Z, and thermic problems were found more frequently with K-X. Additionally, our results suggest that thermic stress may be a relatively frequent complication for Pampas foxes. This study provides baseline data on some physiologic variables in Pampas foxes captured with different methods and drugs in field conditions.

Activity patterns of Molina’s hog-nosed skunk in two areas of the Pampas grassland (Argentina) under different anthropogenic pressure

This study describes and compares the activity patterns of free-ranging Molina’s hog-nosed skunks (Conepatus chinga) in a protected area (PA) and in a cropland area (CA) in the Pampas grassland of Argentina. Sixteen skunks (PA: three males, four females; CA: three males, six females) were captured and monitored using radio-telemetry techniques for 92–395 days each. In both areas, C. chinga was largely nocturnal and the start and cessation of activity was related to sunset and sunrise, respectively. Skunks spent more time active in the PA, where the level of anthropogenic activity was lower, and this difference was due to increased activity during the daylight hours. Finally, activity was greater for females than for males, and in the warm season when compared to the cold season. In the Pampas grasslands of Argentina, activity of Molina’s hog-nosed skunks seems to be influenced by both food availability and predation risk related to human presence.