Factors affecting basking in a northern population of the common snapping turtle, Chelydra serpentina MARTYN E. OBBARD AND RONALD J. BROOKS Department of Zoology, University of Cuelph, Guelph, Ont., Crrnrrda, N l C 2Wl Received June 16, 1978 OBBARD, M. E., and R. J. BROOKS. 1979. Factors affecting basking in a northern population of the common snapping turtle, Chelydru serpentinu. Can. J. Zool. 57: 435-440. Basking behavior was studied in an Ontario population of the common snapping ~urtle. Almt~apheric ha\king was more cammon than previnusly reported in this species. The numhr of atmnsphcric-ha~k~np turtles wac positively correl:tfed with for4 rlaily solar rndiation i~nd with maximr~m air temperature and wa<ngetively co~reliired wi~h to~aId;rily amounl of precipit:~tion. m~ximum water 1ernprrn1iiI-e had little influence on thc numher of .itmospheric-back~ng turtles 7'nrrite\ urually basked alone on ofT5hore lops. Mean (27.TPC) :mil maximum (34.O"C) cl~~acal ternpemtures of atmocpheric-hasking tt~rflcs were ~~gnific:intly ahiwe amhient air remper;ttiire*. OBBARD, M. E., et R. J. BROOKS. 1979. Factors affecting baskingin a northern population of the common snapping turtle, Chelydru serpentinu. Can. J. Zool. 57: 435-440. Lc comprtement des chilydres =+erpenrlne\ qui \e prelasscnt au qoleil a 616 Gtudie chez une popul:ltion d"0nrxria. Le prPlasrernent ;~~rno~phirique est plu\ frequent qu'on ne I'ilvait cru JUF~LI'IL mainteni~nt. 11 y a une correl,ition pus~tive rntre, d'une part. le nombre de iortuer qui \e prclassent ct d'attlre part. la radiatlrrn rul:iire totale cl-line journtie et 1:1 tem~rattur iimhiante maxirn.%le: par cunlre. la corrkl,rtion avec la quantlte 1ot:tle de prkcipitations de lajournrr e\t negi~~ive. [.a tempkr~turernaxlrnale de I'eau a peu d'eflet sur. le nurnb~e de turtues qui \e prdlas~ent au solell. Ley torrue? 5'etcndent r)rclinairemenr ccules sur deb; troncs irner@r. LC< temperature^ cloitultles moyenne (27,RC) cf rnauimale (34.nOC') dez turtuesqui se prel:~\scnt <on1 r~gn11Fc:i1fvement plus Clevees qoe les tem+~-dtnrec am hiilntes dc I'air . [Tradu~t par lejourn,il] Introduction beri), yellow water lily (Nuphar varieguturn), and white water lily (Nyrnph~err oclorata). Maximum depth of the lake is about The common snapping turtle. Ch~!vdr(f .tPrpefr- 9m and the deeper areas, which coincide with the original tirrn, has been described as one of the most aquatic stream bed, are free of floating vegetation. of freshwater chelonians and as a species that Regular circuits of Lake Sasajewun were made by canoe in rarely leaves the water to bask (Pope 1939; Schmidt morning. afternoon, and eveningon 76 days between 9 M~Y and and lnger 1957; E~~~~ and ~~~b~~~ ,972; ~~~~~l~~~ i 23 August. Turtles found lying quiescent on some ob~ect above the surface of the water were described as engaged in atmo- '976). The few Of basking in spheric basking. Turtles floating at the surface or lying in C~P~Y~VU are based on limited oh~ervations (Ewert shallow water with wart of the caravace above the water zurface 197g). In this paper. we provide evidence thar at- mospheric basking may occur commonly in north- ern populations of Chelydra and present the first quantitative description of basking in individually marked snapping turtles. Methods This study was conducted in the southwest portion of Algon- quin Provincial Park, Ont., Canada. This area lies within 150 km of the northern Iimii of the recognized riinge of the common snapping turtle (Logier and Toner 1961 : Conanf 1975). Slitit un hasking anirnds were pthercd fmm Ma!, lo September 1976 on Lake Szrsajewun in the Wildlife Research Area of the Ontitrio Ministry of Natural Resource\ (4735' N, 78"30' W). Add~rion:~l body temperature datii wem collected in 1977. Lake Sasajewun was created in the early 1900's when a dam was bullt on the North Madawaska River. Thus, although the surface area of the lake is about 43 5 ha, much of it covers flooded land, where the water is shallow (< 3m) with numerous upright stumps and floating logs. By late June, these shallow areas are densely covered with water shield (Brasenia schre- - were said to be engaged in aquatic basking (Moll and Legler 1971). When basking turtles were seen, time, location, surface water temperature, air temperature, nature of the basking site, and orientation of the animal were noted. Whenever possible, basking turtles were captured and their cloaca1 temperatures measured, at a depth of 10 cm, within 1 min of capture. All temperatures were measured with a telethermometer to the nearest 0.2"C (model 43, probe #402; Yellow Springs Instru- ment Co., Inc., Yellow Springs, Ohio). A maximum-minimum thermometer, solarimeter, and rain gauge located at the Wildlife Research Station laboratory on the shore of Lake Sasajewun provided daily weather information. Another maximum- minimum thermometer located in Lake Sasajewun at 0.25 m depth measured water temperature. Thiny-five adulr snapping ttlrtles in Lake Sawjewun bore indivirlrrally distinctive metal tags (Lrrncke and Ohhard 1977). which could hr read at ;I distance of 10-20 m using hinoculws and up tu 5b60 m using a 40x ttlrscope. These taps helped ensure that lurtles were counted only once in each basking check. Five males and three fcmales were mdio lagged for vi~ryinp periods in 1976 (thtre m:~les and one female carried radio transmitters all summer). Thus, data were accumulated on known individuals. 0008-4301/79/020435-06$01 .00/0 @ 1979 National Research Council of CanadalConseil national de recherches du Canada