THE INFLUENCE OF MOONLIGHT ON VEGETATION HEIGHT PREFERENCE AND TRAPPABILITY OF SMALL MAMMALS

The trappability of small mammals was compared between moonlit and overcast nights, and between clear and overcast nights, and between clear and overcast days, for different heights of vegetation. Regardless of moonlight, all species captured showed a preference for traps in tall vegetation (approximate to 60 cm), and although wood mice and common shrews were occasionally captured in short vegetation (approximate to 4 cm), bank voles and field voles were not captured there. Bank voles are thought to rely on vegetation cover to avoid predators and by remaining in tall vegetation had no need to respond to cloud cover on moonlit nights. Wood mice, which are thought to rely on speed and agility to avoid predators, were captured in short vegetation, but only when the sky was overcast. Two types of camouflaging trap-covers (cut grass and wooden board) were tested to control for differences in trap visibility that might have contributed to the observed avoidance of short grass on moonlit nights. Wood mice preferred uncovered traps when the sky was overcast but their preference was not affected by vegetation height. The proportion of captures of voles and shrews in covered, as opposed to uncovered, traps was not affected by either cloud cover or vegetation height. It was concluded that the animals were genuinely using plots with short grass less, as opposed to merely avoiding very visible traps.