GREGORY, P. T. 1974. Patterns of spring emergence of the red-sided garter snake (Thamnophis sirtalisparietalis) in the Interlake region of Manitoba. Can. Tlzanmophis s i r t u i i s~, rretalrs * : at , hibernaculum sites in the hterlafe region of Manitoba rats about 1 + monrhs. his perlod is characterized b intense mating sctivlty and a marked excess of males ovrr icrnslcs. Invectiptions b~gun in tie spnng of I970 suggest that these two features are closely linked. Malts begin emerging in large numbers at the end of April and reach a peak population size by mid-May. Ftmales emerge in smaller numbers throughout the entire sprlng p l o d ~tnd are imnrediately approachtd and mated by h e males. A h maring, she I'erniiles disper~e to the summer habitat. Males remain in the vicinity of the hihrnaculum for a longer period, ossibly mating scvcral times, and brpn to disperse in large numbers in the sccond half of &. Ir w sng ested that commum1 clennmg and diKcl.cmial sprlng emergence are mporrant mpects ofl the liie-history strategy of these popula~ions. GREGORY, P. T. 1974. Patterns of spring emergence of the red-sided garter snake (Thamnophis sirtalisparietalis) in the Interlake region of Manitoba. Can. J. Zool. 52: 1063-1069. Au printemps, la pCriode d'activitt de Thamnophis sirtalis parietalis aux sites d'hibernation dure B peu pres 1) mois dans la region Interlake de Manitoba. Cette phiode est caractkriske d'intense activitt sexuelle et d'un excb de maes relativement aux femelles. Des recherches commencEes au grintemps de 1970 suggtrent clue ces deux mract6risriques sont E6esdeprh. Les males cornmencent h Crnerger en grand nombre i la tin d'avril et attclgnent une population maximum au milieu de mai. Les kmeUes emergent en nombre plus perit durant tout le printern s et sont h k d i a t e m e n t a prochees et accoupICes ar les miles. Aprk l'accouplement,Ies Rrne~~es se drsperscnt dans E region d'aclivifk crtiu&. Ler rniiler rericnt autour du site d'hibcrn$on endant quelque temps; ils peuvcnl s'accoupler plua~eurs fo~s, Enfin, ils commencent ;I se Xspcrrer cn grand nornbre dans ir deurikme rnaitie de rnai. I1 est propose que I'hikrnation communde el ces modes differentes d'hcrgence sont des aspects importants de la strategic de vie de ces populations.

No abstract

Previous ecological studies of Thamnophis sirtalis in the Interlake region of Manitoba have concentrated on the spring and fall phases of the annual cycle. This study is an investigation of two aspects of the summer activity of these populations: summer dispersal and feeding habits. Summer dispersal in these animals is highly directional; snakes move south in spring and return north to their hibernation sites in late summer and fall. Large distances are also involved; movements of as much as 17.7 km have been recorded. No explanation of this pattern of dispersal is apparent. Feeding takes place in the summer range only, during June, July, and August. The wood frog (Rana sylvatica) is the most frequently eaten prey species. It is suggested that the short feeding period is the result of a life history strategy which maximizes the efficiency of reproductive activities at the expense of non-reproductive activities.

No abstract

Constraints on time and energy suggest that animals often will have to forgo one activity in favour of another. In the ®eld, gravid garter snakes, Thamnophis elegans, eat little or nothing, especially late in pregnancy. In addition, they spend considerable time basking, presumably to aid development of their progeny. Apparently, therefore, a con¯ict exists between feeding and behaviours related to gestation. Alternatively, low feeding levels in the ®eld might re¯ect reduced ability to catch food while gravid, or anorexia, attributable either to reduced space in the gut or to physiological suppression of appetite. In this study, by supplying abundant food in the laboratory, we test the hypothesis that gravid females are anorexic; we also examine the interactions among feeding, thermoregulation and reproductive condition. Typically, gravid females, whether fed or not, spent most of their time at the warm end of a gradient, as did fed non-gravid snakes; unfed non-gravid females spent signi®cantly less time at the warm end. However, gravid snakes, even when presented with food ad libitum, ate less than non-gravid snakes, suggesting that they are anorexic while pregnant. Feeding and thermoregulatory behaviours of gravid females changed around the time of parturition (increased feeding, reduced warming rate). Comparable changes are seen in animals in the ®eld, and are correlated with changes in movement pattern. Evidently, the tendency to eat little food is carried over into the laboratory, even when apparent proximate causes of the behaviour are removed. Although we cannot distinguish clearly between the two potential causes of anorexia, the evidence slightly favours physiological suppression of appetite. Physiological suppression of appetite while gravid would ensure that the urge to forage rather than thermoregulate does not diminish the chances of present reproductive success. By contrast, non-gravid snakes, faced with a shortage of food, lower their body temperature and reduce their metabolic costs.