Habitat Use and Movement Patterns of Northern Alligator Lizards And
Total Page：16
File Type：pdf, Size：1020Kb
HABITAT USE AND MOVEMENT PATTERNS OF NORTHERN ALLIGATOR COLUMBIA BASIN LIZARDS AND WESTERN SKINKS IN FISH & WILDLIFE SOUTHEASTERN BRITISH COLUMBIA COMPENSATION PROGRAM PREPARED BY Pamela L. Rutherford and Patrick T. Gregory FOR Ministry of Environment, Columbia Basin Fish & Wildlife Compensation Program Lands & Parks BC Fisheries January 2001 IN PARTNERSHIP WITH Columbia Basin Fish & Wildlife Compensation Program 103 - 333 Victoria Street, Nelson, British Columbia V1L 4K3 Phone: (250) 352-6874 Fax: (250) 352-6178 Habitat use and movement patterns of Northern Alligator Lizards (Elgaria coerulea principis) and Western Skinks (Eumeces skiltonianus skiltonianus) in Southeastern British Columbia Pamela L. Rutherford and Patrick T. Gregory Department of Biology, University of Victoria, Victoria, British Columbia, Canada. V8W 3N5: Email: [email protected] HabitatuseandmovementpatternsofNorthernAlligatorLizards(Elgaria coerulea principis) and Western Skinks (Eumeces skiltonianus skiltonianus) in Southeastern British Columbia Pamela L. Rutherford and Patrick T. Gregory Department of Biology, University of Victoria, Victoria, British Columbia, Canada. V8W 3N5: Email: [email protected] ABSTRACT Many reptiles have different requirements for different activities (e.g. hibernation and nesting/gestation) that may not be satisfied by a single location. Suitable habitat may not only be limiting, it may be fragmented, making it difficult for animals to move between sites. Our first objective in this study was to determine the extent to which Northern Alligator Lizards (Elgaria coerulea principis) and Western Skinks (Eumeces skiltonianus skiltonianus) co-occur, in southeastern British Columbia, near the northern limit of both species’ ranges. Our second objective was to determine the characteristics of hibernation and summer sites for both species. Our third objective was to determine the extent of movement in both species, particularly whether migration occurs between summer and winter habitats. We used mark-recapture (PIT-tags and toe-clips) to do this. Both lizard species co-occurred at the same study sites and were found in approximately the same locations in spring, summer and fall. Thus, hibernation apparently occurs in the summer habitat and no seasonal migration occurs. In fact, individuals of either species were 1 recaptured within 10 m (on average) of a previous capture. Both lizard species were rarely found in the open and more often under rocks than in vegetation or under logs; they also remained close to shrubs and forest edges. Roads apparently are not a major concern for either lizard species because they have high site-fidelity and do not make large movements between hibernation or summer sites. Their requirement for cover means that any disturbance or removal of rocks from their habitats would be detrimental to both species. INTRODUCTION Lack of knowledge of the natural history of a species is one of the greatest constraints in conservation planning. Collecting ecological data on reptile species is particularly important as they have typically attracted less attention than other groups, resulting in limited data on their natural history. To date almost half of the 42 Canadian reptile species (Cook, 1984) are of conservation concern (1 extirpated, 4 endangered, 6 threatened, and 8 species of special concern) according to the Committee on the Status of Endangered Wildlife in Canada (COSEWIC, 2000), although not all taxa have been evaluated. This high ratio indicates the importance of describing the natural history and habitat requirements of all Canadian reptiles. Many reptiles have different requirements for hibernation and nesting/gestation (Etheridge et al., 1983; Burger and Zappalorti, 1986; Burger et al., 1988; Prior and Weatherhead, 1996; Litzgus et al., 1999). Description of these sites is of interest to both conservation biologists and population biologists. Identifying hibernation sites is especially important in reptiles that hibernate communally (Gregory, 1984; Litzgus et al., 1999) and return to the same hibernation sites from year to year (Brown and Brooks, 1994; Litzgus et al., 1999). Destruction of communal 2 hibernation sites has occurred in rattlesnakes (Viperidae) as part of ‘rattlesnake round-ups’, resulting in population declines or extirpation from parts of the United States (Galligan and Dunson, 1989; Warwick, 1990). Hibernation site descriptions are also useful for population biologists as part of determining whether a reptile population is limited by availability of suitable hibernation sites (Gregory, 1984). This is particularly important for northern populations as the absence of available hibernation sites may dictate the northern range limits for a population. Populations are limited by available nesting/gestation habitat. In animals that are unable to reproduce every year due to energetic limitations (Aldridge, 1979; Luiselli et al., 1996) it is particularly important that pregnant females complete gestation and avoid predation when reproduction is attempted. Oviparous reptiles require nest sites that provide optimal temperatures and moisture content for developing embryos yet protect them from predators. Nest sites that fit this criterion may be limiting (Cooper et al., 1983; Hecnar, 1994). For viviparous reptiles, selection of basking sites is important because basking by gravid females may increase the risk of predation (Huey and Slatkin, 1976; Shine, 1980; Madsen, 1987) due to their reduced mobility (Vitt and Congdon, 1978; Bauwens and Thoen, 1981; Shine, 1980; Seigel et al., 1987; Brodie, 1989; Cooper et al., 1990; Sinervo et al., 1991). Because the requirements for hibernating and reproducing are quite different they may not be satisfied by a single location and animals may need to travel long distances between these sites (Weintraub, 1966; Gregory and Stewart, 1975; Brown and Parker, 1976; Brown and Brooks, 1994). Movement between sites may be difficult if the habitat has become fragmented. This has occurred in many terrestrial habitats (Diamond et al., 1987; Saunders et al., 1991). There will be additional difficulty if there are barriers between the hibernation habitat and the summer habitat. Roads are common barriers that isolate habitats, deter the movement of wildlife and cause 3 extensive wildlife mortality (Oxley et al., 1974; Case, 1978; Dalrymple and Reichenbach, 1984; Garland and Bradley, 1984; Mader, 1984; Bernardino and Dalrymple, 1992; Rosen and Lowe, 1994; Ashley and Robinson, 1996; Trombulak and Frissell, 2000). In addition, paved roads retain heat and many snakes will bask on the pavement increasing their likelihood of being killed (Bernardino and Dalrymple, 1992; Ashley and Robinson, 1996). The effect of roads on small lizards has not been investigated and it is important to determine if roads represent barriers between habitat patches or if they result in high mortality due to basking, as is the case with snakes. Hibernation sites, summer habitat, and basic movement biology have not been described for the only two common lizard species found in British Columbia, which comprise two of the five native lizard species in Canada: 1) the Northern Alligator Lizard (Elgaria coerulea principis) or 2) the Western Skink (Eumeces skiltonianus skiltonianus). Our first objective in this study was to determine the extent to which Northern Alligator Lizards (Elgaria coerulea principis) and Western Skinks (Eumeces skiltonianus skiltonianus) co-occur, in southeastern British Columbia, near the northern limit of both species’ ranges. Our second objective was to determine the characteristics of hibernation and summer sites for both species. Our third objective was to determine the extent of movement in both species, particularly whether migration occurs between summer and winter habitats. We used mark-recapture (PIT-tags and toe-clips) to do this. In addition to addressing fundamental questions about the biology of these animals, our results also have important implications for their management. 4 METHODS Species Description The Northern Alligator Lizard (Elgaria coerulea principis) is a small lizard with a long, slender body and short legs. It is brown in color, and frequently has dark blotches that vary between sexes and populations (Gregory and Campbell, 1984). It is viviparous, having one litter per year; four to six young on average (Vitt, 1974). It is diurnal, thermoregulates by basking, and is active at body temperatures ranging from 20 to 30 ˚ C (Vitt, 1973). The Western Skink (Eumeces skiltonianus skiltonianus) is a small slender lizard with a pointed head and short legs. It has a broad brownish band down its back, flanked by white stripes. The young have a bright blue tail tip that fades as they age (Gregory and Campbell, 1984). They are oviparous and lay one clutch per year. Eggs are deposited in excavations dug under rocks or other cover objects. Clutch size varies from two to five and the female frequently stays with the eggs until they hatch. It is diurnal and thermoregulates by basking (Gregory and Campbell, 1984). Distribution Northern Alligator Lizards are found in southern British Columbia, south to the Sierra Nevada of California, and east to the northern tip of Idaho and northeastern Montana (Fig. 1). In Canada, the Northern Alligator Lizard (Elgaria coerulea principis) occurs in southern British Columbia, including Vancouver Island and the Gulf Islands. Within this range it is absent only from the southeastern corner of the province (Fig. 2). The Western Skink (Eumeces skiltonianus