The Local Ecological Effect of Long Tailed Jaegers Nesting in the Subarctic

Abstract

While carrying out geomorphological field work in the Ruby Range, Yukon Territory ... during the summers of 1967 and 1968, an extension of the known breeding grounds of the long tailed jaeger (Stercorarius longicaudus) was observed. A pair of these birds nested on the same southeast-facing slope both years and their presence affected the local ecology in significant ways. For example, they maintained a constant vigil and promptly chased away any predator which came close to the slope. This provided an umbrella for other animals on the slope such as ground squirrels, pika, marmot, and ptarmigan. As a result the population of these animals was higher and their behaviour was more uninhibited than in surrounding areas. This became even more noticeable, by contrast, upon returning to the field in the summer of 1972 and finding the jaegers missing. The feather remains of one adult jaeger were discovered and the atmosphere on the slope was very different. ...Although the Ruby Range is approximately 900 km south of the previously documented nesting area of the long tailed jaeger, several jaegers were sighted here. My research was concerned with solifluction lobe development in the Ruby Range and detailed work was carried out on four adjacent slopes facing southeast, southwest, east, and north. ... The jaegers' nest was located in approximately the same place both years, on a lobe tread in a small basin between two mossy hummocks. ... Occasionally we would hear the jaegers begin their high shrill calls and look in the direction they were flying to see an eagle .... The same treatment was allotted other predators such as wolf, fox, bear, and wolverine. ... The virtual elimination of predators from the slope during the summer was somewhat counterbalanced by the jaegers themselves, however, since they harvested many small rodents on the slope, i.e., shrews, lemmings, voles, and mice of various kinds. But for the larger burrowing mammals, such as ground squirrels, pika, marmot, as well as the ptarmigan, it provided a rather trouble-free existence. On a comparative basis the population of burrowing animals was vastly greater on the southeast-facing slope than the other exposures, and although the major explanation for this may be because of the more favourable environment on the south-east, it is nevertheless felt that the jaegers' presence contributed significantly to the relatively high population. ... there was a clear and observable difference in the ecology of the slope because of the jaegers' presence. Such ecological relationships are replete in nature and we have a great deal to learn about and from them.