Serge Larivière

INTERACTIVE EFFECTS OF VEGETATION AND PREDATORS ON THE SUCCESS OF NATURAL AND SIMULATED NESTS OF GRASSLAND SONGBIRDS

Abstract We examined the influence of vegetation and predator community on nesting success of songbirds in the grasslands of eastern North Dakota, USA. Each year, eight sites were chosen: four were subject to predator removal, and four were non-removal sites. On each site, nests of grassland songbirds were monitored, and simulated nests were used to examine how vegetation characteristics at nests affect nest success. Vegetative characteristics at simulated nests did not differ from those at natural nests, but successful natural nests had greater forb and lesser grass cover than unsuccessful nests, whereas no differences in vegetation were detected between successful and depredated simulated nests. On non-removal sites, small mammals and ground squirrels (Spermophilus sp.) depredated nests in taller and denser cover when compared to nests destroyed by medium-sized mammals and birds. On removal sites, we found no difference in vegetation characteristics of nests depredated by different predator types. However, each group of mammalian predators depredated simulated nests with different vegetation characteristics on removal versus non-removal sites. On sites where predators were removed, small mammals and ground squirrels preyed on simulated nests in shorter vegetation containing fewer forbs, ground squirrels preyed on nests with higher grass cover and lower vertical density, and medium-sized carnivores preyed on nests in taller vegetation. These results support the hypothesis that high predator diversity may reduce the chance of “safe” nest sites, and suggest that the behavior of low-level predators may change when top-level predators are removed.

EVOLUTION OF INDUCED OVULATION IN NORTH AMERICAN CARNIVORES

Abstract We tested the hypothesis that induced ovulation is adaptive in North American carnivores by providing a mechanism to overcome the risk of unsuccessful mating in solitary species living in seasonal environments and a method for females to evaluate male quality via sexual selection inside the reproductive tract. We obtained published data on North American carnivores and determined from their distribution a coefficient of seasonality and primary productivity. Using traditional statistics and comparative methods, we determined that induced ovulators lived in more seasonal environments apparently not influenced by energy. No statistical differences in behavioral traits existed between induced and noninduced ovulators, but trends in data were consistent with our predictions, with induced ovulators tending to have larger home ranges and longer estrous periods. Mating systems also differed between the groups: induced ovulators were characterized by mostly (93%) multimale mating systems, whereas noninduced ovulators were monogamous (42%), multimale (33%), or polygynous (25%). Also, induced ovulators exhibited larger sexual dimorphism and smaller neonates than noninduced ovulators or felids. We suggest that induced ovulation evolved through sexual selection as a reproductive strategy beneficial for males (assurance of egg fertilization during short pair bonds) and females (postcopulatory mate choice based on level of stimulation causing induced ovulation).

Range expansion of raccoons in the Canadian prairies: review of hypotheses

Abstract The raccoon (Procyon lotor) has greatly expanded its range in the Canadian prairies during the 1900s. Four non-exclusive explanations may explain this range expansion: introductions, mesopredator release, availability and suitability of winter denning sites, and food availability. No introductions of raccoons were documented for the prairies, suggesting that range expansion was not directly caused by humans. The suggestion that raccoons moved north because of “mesopredator release” appears implausible because, even where larger predators such as bobcats (Lynx rufus) and coyotes (Canis latrans) exist, raccoons experience low predation rates and also because raccoons have expanded their range into treeless areas where coyotes are abundant. The third hypothesis, suggesting that availability of winter denning sites limits raccoon distribution, also receives little support, mostly because of the raccoons flexibility in using a variety of natural and anthropogenic structures for denning. The last hypothesis, the idea that raccoon range expansion has followed an increase in availability of food, appears most plausible. The effects of global warming, which affects not only the availability and diversity of foods but also the duration of the growing season (and thus temporal availability of food), probably helped raccoons colonize new areas.

Energetic Consequences and Ecological Significance of Heterothermy and Social Thermoregulation in Striped Skunks (Mephitis mephitis)

We assessed patterns and energetic consequences of different overwintering strategies, torpor, and social thermoregulation in the striped skunk (Mephitis mephitis) under natural ambient temperature and photoperiod. Striped skunks entered spontaneous daily torpor, with the lowest torpid body temperature (Tb) reaching 26.0°C, the lowest recorded Tb for a carnivore. Patterns of daily torpor differed between solitary and grouped skunks: all solitary skunks regularly entered daily torpor, but only some individuals in communal dens employed torpor. When they did, it was shallow and infrequent. Solitary skunks entered torpor on average 50 times (in 120 d) compared with 6 times for grouped skunks. During torpor, solitary skunks had average minimum Tb of 26.8°C and bout duration of 7.8 h, whereas grouped skunks had average minimum Tb of 30.9°C and bout duration of 5.4 h. Torpor by solitary skunks occurred during their activity phase, but grouped skunks’ shallow torpor bouts were restricted to their diurnal resting phase. On average, grouped skunks experienced lower percent daily fat loss, and they emerged in spring with higher percent body fat of 25.5%. In contrast, solitary skunks emerged in spring with only 9.3% body fat. In conclusion, the use of daily torpor and social thermoregulation in northern populations of striped skunks represent two strikingly different mechanisms to minimize energetic costs and increase individual fitness in response to unfavorable environmental conditions.

Spatial organization of a prairie striped skunk population during the waterfowl nesting season

Information on the spatial organization of the striped skunk (Mephitis mephitis) is required for the management of this species as a predator of waterfowl eggs. Radiocollared striped skunks were tracked in southcentral Saskatchewan from April through August, 1993 (6 M, 13 F) and 1994 (2 M, 15 F). Home ranges (100% minimum convex polygon) of males (11.6 ± 2.8 km 2 , n = 5) were larger (P < 0.01) than those of females (3.7 ± 0.3 km 2 , n = 21). Similarly, core areas of males (3.0 ± 1.2 km 2 ) were larger (P < 0.01) than those of females (1.0 ± 0.1 km 2 ). Extensive intrasexual overlap occurred among home ranges (71 ± 4%) and core areas (26 ± 7%) of females. Daily ranges of striped skunks did not vary with sex or biological season (preparturition, parturition-rearing, predispersal, dispersal), and averaged 1.39 ± 0.26 km 2 for males and 1.11 ± 0.17 km 2 for females. Neither males nor females scent-marked, and all individuals were solitary (except females with young). Females are likely more important predators of duck eggs than males because females are more abundant, have overlapping ranges, and travel their home ranges more intensively.

Evaluating body condition of striped skunks using non-invasive morphometric indices and bioelectrical impedance analysis

Abstract Assessment of the body composition and body condition of animals in the wild is an important aspect of animal ecology. We were interested in understanding the seasonal changes in body condition in order to investigate the effects of adaptive strategies on life histories of animals. We investigated the merit of morphometric condition indices and bioelectrical impedance analysis (BIA) to predict fat reserves in striped skunks (Mephitis mephitis, n = 26). We took BIA and morphometric measurements following chemical immobilization in the field and completed chemical analyses of whole carcasses postmortem. We determined relationships between body lipid and water using multiple linear regression techniques and performed model selection using Akaikes Information Criterion (AIC). Bioelectric volume (L2/Rs) and chest circumference (CC) best predicted total body water (TBW=–1.1+0.058*CC+0.25 * L2/Rs; r2 = 0.91, SEE=0.15, P <0.001). Lean dry mass (LDM) was significantly correlated with total body mass (LDM=0.26+0.12 * TBM; r2=0.63, SEE=0.13, P<0.001). Total body fat (TBF) can then be estimated using total body water and lean dry mass by the equation TBF=TBM–TBW–LDM. We found condition indices to be poor indicators of body condition in striped skunks. Use of BIA on striped skunks has implications for a fast and accurate method to estimate body condition under field conditions.

Selection by Striped Skunks (Mephitis mephitis) of Farmsteads and Buildings as Denning Sites

Abstract In the Canadian prairies maternal dens of striped skunks (Mephitis mephitis) are often located under a building in a farmstead. However, not all farmsteads or buildings are used by skunks, suggesting that striped skunks have specific preferences. To test this hypothesis, we measured a variety of parameters of farmsteads and buildings present in an area where striped skunks were intensively radio-tracked from 1993–1995. Farmsteads that were used by skunks as maternal dens or resting sites did not differ from unused farmsteads by number of buildings, degree of use by humans, distance to water or habitat availability within a 1-km radius. However, buildings that were used for dens could be differentiated from buildings not used for dens by the presence of a closed space underneath them. The presence of a closed space underneath a building floor is important for striped skunks, possibly because of low construction and maintenance costs of dens, thermoregulatory advantages and reduced predation risk. Abandoned buildings suitable for skunks may be managed by removal, or by more effective exclusion or trapping of resident skunks.

CONDITION INDICES AND BIOELECTRICAL IMPEDANCE ANALYSIS TO PREDICT BODY CONDITION OF SMALL CARNIVORES

Abstract Body condition directly affects survival and reproduction by animals, so its effects on fitness represent an important component of animal ecology. Traditionally, ecologists have relied on direct chemical analysis or morphometric indices to assess body condition. We examined the ability of morphometric indices and bioelectrical impedance analysis to estimate body condition of raccoons (Procyon lotor) and assessed the need for species-specific models. Morphological indices were poor estimators of body condition; the best model explained 62% of the variation of fat and had a high SE (r2 = 0.62, SE = 0.52, P < 0.001). Bioelectrical impedance analysis proved to be a reliable way to noninvasively estimate body condition. Models for lean dry mass and total body water were used to accurately estimate body fat (r2 = 0.94, SE = 0.16, P < 0.001). Body fat estimates derived through models for a similar species performed better than morphometric indices but did not achieve the accuracy of the species-specific model. Examination of our data highlights the need to validate models used to estimate body condition before use.

Social organization and group formation of raccoons at the edge of their distribution

Abstract We examined spatial and temporal relationships of 104 raccoons (Procyon lotor) at the northern edge of their distribution to report social organization and to test hypotheses regarding the formation of coalition groups among adult male carnivores. Social tolerance among females varied among years, but adults maintained relatively exclusive home ranges (overlap ranged from 2.2% to 12.5%) that were dispersed in a uniform pattern throughout the duration of the study (Clark–Evans ratios ranging from 1.32 to 1.87, P < 0.001–0.08). Social interactions among males were more complex than previously described for low-density populations of raccoons, with most adults (approximately 80%) forming coalition groups. We identified 9 unique coalitions that had extensively overlapping home ranges and positively associated nightly movements within group members (overlap indices ranging from 85.3% to 97.3%). Coalitions maintained exclusive territories between groups (overlap indices ranging from 0% to 3.2%) and formed distinct spatial boundaries that were highly correlated with home-range boundaries of females. Male coalition groups in the order Carnivora are hypothesized to form in response to aggregations of females, but examination of our data suggests that this is not a prerequisite for their formation. We propose a dominance hierarchy where subordinate males benefit through increased likelihood of inheritance of territories, whereas dominant males benefit through increased efficiency of territorial defense.

Diseases and pathogens of Mustela spp, with special reference to the biological control of introduced stoat Mustela erminea populations in New Zealand

Controlling populations of introduced stoats is a high priority for the conservation of avian biodiversity in New Zealand Existing technology for stoat control is labour intensive and expensive, therefore new techniques and approaches, such as biological control, are needed We reviewed the literature on the diseases and pathogens of stoats, and closely related mustelids, with a view to identifying potential biological control agents Aleutian disease virus, mink enteritis virus, and canine distemper virus hold promise as agents of lethal control, though the risks to non‐target species posed by these viruses are serious Host‐specific ectoparasites such as Tnchodectes ermineae, nematodes such as Skrjabingylus nasicola, and bacteria such as Hehcobacter mustelae and Bartemella spp could have a role as vectors for the transmission of fertility control agents We urge some caution in developing biological control technology without a parallel investigation of the potential effects of biological control on stoat populations and the resulting survival of threatened birds