Monday, October 25, 2010
Snakebite, Snake Activity and Climate
But the El Nino-La Nina cycle does not only effect snakes and snakebite in Australia. Morrison and Bolger (2002) monitored reproductive success of individual rufous-crowned sparrows (Aimophila ruficeps) in coastal sage scrub habitat of southern California from 1997 to 1999. They found annual reproductive output of this ground-nesting bird varied strongly with annual variation in rainfall. Birds fledged 3.0 young per breeding pair in 1997, when rainfall was near the long-term mean, 5.1 offspring per pair in 1998, a wet El Niño year. But in the drier 1999 La Niña year only 0.8 fledglings were produced per pair. The reproductive output was consistent with the hypothesis that food availability was positively correlated with rainfall. But, the factor most responsible for the high reproductive output in 1998 was low early season nest predation which, combined with favorable nesting conditions, enabled more pairs to multiple-brood. Cool, rainy El Niño conditions in 1998 altered the activity of snakes, the main predator of these nests. The authors used video-surveillance of nests and found the California Kingsnake (Lampropeltis getula californiae) and the San Diego Gopher Snake (Pituophis melanoleucus annectens) were the principal nest predators and that they account for 90% of the predation events, where the predators could be identified. More recently, González-Andrade and Chippaux (2010) evaluated the burden of snake bite in Ecuador in an attempt to identify the difficulties of snake bite management in the country's health facilities. They surveyed national health statistics to estimate the overall incidence and mortality due to snake bites. From1998–2007, the average annual incidence and mortality was respectively 11 and 0.5 per 100 000 inhabitants. The Ecuadorian snakebite incidence increased in the rainy season and in El Niño years. Snake activity changes with cllimate, a simple concept but one with far reaching consequences that are seldom appreciated.
Morrison, S. and D. Bolger. 2002. Variation in a sparrow's reproductive success with rainfall: food and predator-mediated processes. Oecologia 133: 315-324.
González-Andrade, F. and J.-P. Chippaux. 2010. Snake bite envenomation in Ecuador. Transactions of the Royal Society of Tropical Medicine and Hygiene, 104:588-591.