The Effect of Weather on Bioenergetics of Breeding American Woodcock

Simulation modeling was used to investigate the impact of weather on the bioenergetics of breeding and postbreeding American woodcock (Scolopax minor). Using air temperature and precipitation as inputs, the model calculates the daily energy requirements of an adult female woodcock and chicks along with the availabilty of their primary food, earthworms (Lumbricidae). Energetics were modeled from previous studies on woodcock and related species. Earthworm availability was modeled from field data collected in northern Michigan. Results suggest that the greatest potential for weather-related stress on woodcock occurs during the brood-rearing period, with nesting being the 2nd most critical time' When simulated earthworm availability during the brood period was compared with reproductive success data, it indicated that the impact of spring weather on earthworm availability is a significant factor affecting chick survival. J. WILDL. MANAGE. 47(3):762-771 Weather patterns are known to affect woodcock behavior and extremes are a suspected cause of mortality. Studies have shown that cold spring temperatures cause a decline in singing male activity (Duke 1966) and that temperature and wind in combination affect the timing of spring and fall migrations (Sheldon 1971, Godfrey 1974, Coon 1977). However, little is known about the influence of weather on mortality, largely because of the difficulty in finding woodcock and determining the cause of death. Mendall and Aldous (1943) reported instances of nest losses and adult mortality on the breeding grounds following an extended period of inclement weather, and Sheldon (1971) and Owen (1977) believed adverse weather during incubation and brood-rearing can cause significant chick mortality. Earthworms, which comprise 60-90% of the woodcock diet (Aldous 1939, Sperry 1940, Glasgow 1958, Sheldon 1971), are also affected by weather. Reproduction and growth rates have been shown to decline outside an optimal temperature range (Evans and Guild 1948, Satchell 1955). More important to woodcock, however, is the strong influence that soil moisture and temperature have on earthworm activ ty and vertical distribution in the soil. When conditions near the surface become suboptimal, earthworms respond by either migrating deeper in the soil or entering a state of aestivation (Guild 1948, Reynolds and Jordan 1975, Edwards and Lofty 1977) and become unavailable to feeding woodcock. Our objective was to evaluate the direct and indirect effects that weather can have on woodcock energetics and to identify periods of greatest potential impact. Because of the inherent difficulties in gathering field data, simulation modeling was used to examine the relationship between energy requirements of woodcock and food availability. We thank D. Beaver and G. Dudderar, Michigan State University, and C. BenMichigan Agricultural Experiment Station Paper 10251. 2 Present address: School of Natural Resources, University of Michigan, Ann Arbor, MI 48109. 762 J. Wildl. Manage. 47(3):1983 This content downloaded from 207.46.13.149 on Mon, 03 Oct 2016 06:01:28 UTC All use subject to http://about.jstor.org/terms WOODCOCK BIOENERGETICS * Rabe et al. 763 nett, Michigan Department of Natural Resources, for reviewing earlier drafts of this manuscript. We also thank J. Tautin, U.S. Fish and Wildlife Service, for supplying detailed harvest reports for Michigan. This work was supported by the Accelerated Research Program for Migratory Shore and Upland Game Birds, U.S. Fish and Wildlife Service contract 14-16-00082092, and the Michigan State University Agricultural Experiment Station.