Lemmus lemmus: A Possible Case of Aposematic Coloration and Behavior

Abstract

The Norwegian lemming ( Lemmus lemmus L.) differs from sympatric rodents in its conspicuous yellow, red-brown, white, and black coloration, and in its noisy, aggressive behavior towards man and predators. It is suggested that these features are aposematic, making a lemming identifiable at a distance, and giving it some protection against predators. This requires that, in the lemming range, there are 1) sympatric small rodents and 2) important rodent predators 3) for which the lemming is less suitable prey than other rodents. Points 1 and 2 are supported by available range data. Point 3 was tested by presenting lemmings and grey-sided voles ( Clethrionomys rufocanus ) in field tests to an avian predator, the long-tailed jaeger ( Stercorarius longicaudus ). The jaeger took significantly fewer lemmings than voles. Lemmings, but not voles, made active defence, and usually deterred the predator. Also, in relation to voles, lemmings occurred significantly less often in jaeger pellets than their numbers in the field would predict. Larger size and correspondingly better defence ability than in sympatric rodents probably lend survival value to aposematic coloration and behavior in the Norwegian lemming. The color of the Ob lemming ( L. obensis ) is possibly also aposematic, whereas the brown lemming ( L. trimucronatus ) is inconspicuously colored. The brown lemming in a large part of its range is sympatric only with one small rodent, the similarly sized Dicrostonyx groenlandicus , and hence probably would gain no advantage from being aposematic.