Quality of selection-logged and unlogged forests for breeding yellow-bellied sapsuckers.

摘要

I tested hypotheses concerning the effects of food, nest predation, and nest sites on habitat quality for breeding Yellow-bellied Sapsuckers (Sphyrapicus varius) in selection-logged and unlogged hardwood forest stands in Algonquin Provincial Park, Ontario. I focused on this species because its abundant nest holes and sap wells provide shelter and food, respectively, for several other animals. Nest predation by American black bears (Ursus americanus) negatively influenced reproductive success in tolerant hardwood stands 1--25 years following selection logging, whereas nest predation by bears was much less prevalent within tolerant hardwood stands >60 years post-harvest and within unlogged intolerant hardwood stands. Nest-tree limitation in logged stands may have caused the pattern, because with fewer high-quality choices sapsuckers may have been unable to find ideal sites, and as a result excavated in softer wood, which made nests vulnerable to predation by black bears. From 1--5 years post-harvest, when ideal nest trees were most limited, predation by bears was common enough (∼50%) that population growth was likely negative. Sapsuckers preferred 1--5 year cuts, however, making them ecological traps. Increasing high-quality nest trees in 1--5 year cuts may increase the proportion of nests excavated in bear-resistant substrates, which will reduce nest predation and increase fecundity. Fecundity was highest in >60 cuts followed closely by unlogged intolerant stands; I speculate that the difference may be caused by delayed egg-laying as a result of lower-quality sap resources in unlogged intolerant stands. I also reviewed literature across several species to assess whether simultaneously increasing food and reducing predation as a conservation strategy to increase fecundity is more effective for populations of animals that produce a single brood or litter followed by a non-breeding period versus populations that produce multiple broods or litters one after the other. Given that the Yellow-bellied Sapsucker is single-brooded, any positive response to a strategy that increases food and reduces nest predation will be smaller, and take longer, than if it were multi-brooded. My thesis illustrates the advantages of simultaneously assessing the effects of the most important ecological factors limiting reproductive success.;Key words: American black bear, cavity nest site selection, ecological trap, fecundity, food limitation, habitat quality, keystone species, predation, reproductive success, single-tree selection logging, Sphyrapicus varius , synergism, tree harvesting, Ursus americanus, Yellow-bellied Sapsucker.