Sm. Secor et Ka. Nagy, BIOENERGETIC CORRELATES OF FORAGING MODE FOR THE SNAKES CROTALUS-CERASTES AND MASTICOPHIS-FLAGELLUM, Ecology, 75(6), 1994, pp. 1600-1614
Foraging mode may influence an array of ecological and bioenergetic ch
aracteristics, several of which we compared between two snakes: sympat
ric sit-and-wait foraging sidewinders, Crotalus cerastes, and widely f
oraging coachwhips, Masticophis flagellum. During the majority of surf
ace activity, the nocturnal C. cerastes were either coiled on or parti
ally buried in the sand waiting to ambush mobile prey, whereas the diu
rnal M. flagellum cruised through the habitat searching for active and
sedentary prey. Average duration of daily surface activity of C. cera
stes ((X) over bar +/- 1 SE = 7.2 +/- 0.7 h/d) was nearly twice that o
f M. flagellum (3.9 +/- 0.9 h/d). Body temperatures (T-b's) of active
M. flagellum (33.1 degrees +/- 0.1 degrees C) averaged higher, and wer
e maintained within a narrower range, than those of active C. cerastes
(25.3 degrees +/- 0.1 degrees C). Field metabolic rates (FMR, as CO2
production), measured with doubly labeled water, were significantly gr
eater in M. flagellum (body mass = 124 +/- 12 g [(X) over bar +/- 1 SE
]) than in C. cerastes(125 +/- 6 g) during the active season (mid-Apri
l to mid-October; 0.154 +/- 0.017 vs. 0.063 +/- 0.005 mL.g(-1).h(-1)),
transition seasons (mid-March to mid-April, mid-October to mid-Novemb
er; 0.058 +/- 0.009 vs. 0.028 +/- 0.002 mL.g(-1).h(-1)), and hibernati
on (mid-November to mid-March, 0.014 +/- 0.002 vs. 0.007 +/- 0.001 mL.
g(-1).h(-1)). Masticophis flagellum also possessed significantly great
er rates of water influx than C. cerastes during the active (19.7 +/-
2.9 vs. 7.6 +/- 1.1 mL.kg(-1).d(-1)) and transition seasons (7.1 +/- 1
.8 vs. 2.5 +/- 0.5 mL.g(-1).d(-1)). Standard metabolic rates (SMR), me
asured at six T-b's (10 degrees-35 degrees C), of M. flagellum average
d 37 +/- 4% greater than SMR of C. cerastes. The monthly metabolic cos
t of SMR, calculated by integrating 24-h T-b profiles with temperature
-dependent regression equations for SMR, averaged 62 +/- 4% greater fo
r free-ranging M. flagellum than for C. cerastes. The difference betwe
en FMR and SMR is the energy allocated to activities and other energy-
demanding functions such as digestion and represented 65 and 76%, resp
ectively, of the yearly metabolic expenditure of C. cerastes and M. fl
agellum. Annually, M. flagellum spent 2.6 times the amount of energy o
n activity and other functions as did C. cerastes. Contributing to exp
enditures above SMR were digestion (19-43% of FMR) and movement (6-18%
of FMR). Feeding rate (calculated from water influx) during the activ
e season of M. flagellum (24.1 +/- 5.5 g.kg(-1).d(-1)) was more than t
wice that of C. cerastes(9.4 +/- 1.4 g.kg(-1).d(-1)). Over a full year
, M. flagellum consumed 2.1 times as much assimilable energy as did C.
cerastes, although both species gained similar energy profits (212 an
d 177 kJ/yr, respectively). The foraging strategy of the cryptic, ambu
shing C. cerastes balances low energy expenditure with low food intake
, whereas widely foraging M. flagellum have greater expenditures but a
chieve greater energy consumption, as well.