Female Agassiz’s desert tortoise activity at a wind energy facility in southern California:The influence of an El Nino event

We compared spring-summer activity of adult female Agassiz’s Desert Tortoises (Gopherus agassizii) among three consecutive years (1997, 1998, and 1999) that differed dramatically in winter rainfall and annual plant production at a wind energy facility in the Sonoran Desert of southern California. Winter rainfall was approximately 71%, 190%, and 17% of the long-term average (October-March = 114 mm) for this area in water years (WY) 1997, 1998, and 1999, respectively. The substantial precipitation caused by an El Ni?o Southern Oscillation (ENSO) event in WY 1998 produced a generous annual food plant supply (138.2 g dry biomass/ m2) in the spring. Primary production of winter annuals during below average rainfall years (WY 1997 and WY 1999) was reduced to 98.3 and 0.2 g/m2, respectively. Mean rates of movement and mean body condition indices (mass/length) did not differ significantly among the years. The drought year following ENSO (WY 1999) was statistically similar to ENSO in every other measured value, while WY 1997 (end of a two year drought) was statistically different from ENSO using activity area, minimum number of burrows used, and percentage of non-movements. Our data suggest that female G. agassizii activity can be influenced by environmental conditions in previous years.

Relationships among rat numbers,abundance of oil palm fruit and damage levels to fruit in an oil palm plantation

The relationships between vertebrate pests and crop damage are often complex and difficult to study.In palm oil plantations rodents remain the major pests,causing substantial monetary losses.The present study examined the numerical and functional responses of rodents to changes in the availability of oil palm fruit and the damage associated with that response.For the study,200 traps were set in pairs on a 10×10 trapping grid for 3 consecutive nights in each of 6 study plots at 8-week intervals in a 2569 ha oil palm plantation at Labu,Negeri Sembilan state in Peninsular Malaysia over 14 months.A total of 1292 individual rats were captured over 25200 trap-nights.Animals were identified,aged,sexed,weighed and measured.An index of the relative abundance of rats was calculated based on trapping success.Damage to infructescences was assessed at each trap point.Regardless of the age of palms,there were positive and significant relationships between the relative abundance of rats and numbers of infructescences.The levels of damage to infructescences were significantly correlated with the relative abundance of rats.A steep increase in damage was observed with an increase in mature infructescences,indicating a feeding preference of rats for mature infructescences.For both males and females of all rat species,there were weak and non-significant correlations between body condition and infructescence numbers.These results indicated that there was a numerical and a functional response by rats to the availability of palm fruit and a resulting increase in depredation of oil palm fruits.The ways in which this information might aid in future pest control are discussed.