Neotropical migrant banding program at the University Field Station, Delta Marsh, 1993 Keith A. Hobson Canadian Wildlife Service 115 Perimeter Road, Saskatoon, Saskatchewan, Canada S7N 0X4 E-mail: hobsonk@saskatoon2.wxe.sk.doe.ca

Neotropical migrant songbirds, those species that winter in the American neotropics (including primarily Central America, northern South America, and the islands of the Caribbean), and breed in temperate North America, appear to be declining dramatically. However, despite growing concern over the plight of neotropical migrant passerines breeding in Canada, little information exists on population trends of these species, particularly throughout the western provinces. Indeed, much of our current concern is based on population declines documented for migrants that move through and breed in the hardwood forests of the eastern United States and it is not known to what extent these trends may be valid throughout the continent (Askins et al. 1990; Robbins et al. 1989). This paucity of data on populations of neotropical migrants occurring in the Prairies has prompted the Canadian Wildlife Service and the Long Point Bird Observatory to establish or support monitoring stations at Last Mountain Lake in Saskatchewan and Beaverhill Bird Observatory in Alberta. Routine mistnetting and banding at these stations will help us establish population status and reproductive success of several species that breed over broad geographic areas. However, these efforts will not allow us to establish historical population trends in this region. Fortunately, a banding study conducted in the early 1980s has provided an excellent opportunity to monitor possible declines of warblers moving through south-central Manitoba.

From 1982 to 1984, Heidi den Haan, under the supervision of Dr. Spencer Sealy of the Department of Zoology, University of Manitoba, conducted spring and fall banding of warblers moving through the narrow dune forest along the south shore of Lake Manitoba. This area is an ideal location to mistnet migrant songbirds because it is bordered on one side by the Lake and on the other by Delta Marsh. Migrants are thus likely to stop at and move along this strip of forest before continuing on their way to the breeding or wintering grounds. The recent interest in the status of neotropical migrants by CWS and the willingness of Dr. Sealy and Heidi den Haan to collaborate in a follow-up study has provided the necessary impetus for our recent three-year program established at the University Field Station (Delta Marsh) in 1992. This report summarizes banding results for the 1993 field season.

Methods

In July of 1993, eleven mistnet sites were established at the same positions as used previously in 1992 and by den Haan and Sealy in the early 1980s. These sites are located between the Station and the Assiniboine River Diversion. All mistnets are standard 3x12 meter, four-tier design. In keeping with the 1982-84 protocol, half of the mistnets were 30 mm mesh and the other half 36 mm mesh. Mistnets were operated typically for six hours after one half hour before sunrise and again for two hours in the late afternoon or early evening. Nets were checked every 20-30 minutes or more frequently when necessary. All birds were banded and mass, wing length, furculum fat level measured. In addition, where possible, age and sex was determined through plumage characteristics, skulling and evidence of breeding status (presence of a brood patch or cloacal protuberance). Presence of molt and feather wear was also recorded for each individual. During the banding season of 1993, blood and feather samples were taken from a subset of birds captured to be used in genetics and stable-isotope analysis. Starting in 1993, we also incorporated several recommendations of the Long Point Bird Observatory (LPBO). In particular, we established Daily Estimated Totals (ET) of all birds recorded in the vicinity of our banding station. As originally conceived at LPBO, the ET was designed to incorporate the advantages of several sampling procedures while minimizing the disadvantages of relying on any single method. At Delta Marsh, the ETs are based on banding totals, a daily hour-long census along a route incorporating the Ridge forest, Delta Marsh and the shoreline of Lake Manitoba, and other incidental but more or less continuous observations by banders and observers.

Results

Data summaries and trend analysis will be performed following the three-years of data collection. From 14 July through 30 September 1993, 4021 captures were recorded representing 76 species (Table 1). Dramatic increases in the numbers of captured Ruby-crowned Kinglet, Tennessee Warbler and Yellow-rumped Warbler were found in 1993 compared with 1992.

Comments

Following the research component of this project it is hoped that a permanent banding station will be established at the University Field Station (Delta Marsh). Currently, there is ample opportunity for volunteer help at the Station between mid-July and the end of September and all interested individuals are encouraged to contact the author.

Acknowledgements

This project has relied exclusively on the dedicated banding efforts of many individuals. In particular, I thank Paula Grieef for supervising the program and Marlene Gifford, Heidi den Haan and Enid Cumming for their enthusiastic support. Dr. Spencer Sealy and Heidi den Haan made this project possible by providing banding data from the early 1980s. Special thanks to the staff and students of the University Field Station (Delta Marsh) for their generous support. Financial assistance was provided by the Canadian Wildlife Service and the James L. Baillie Memorial Fund.

Literature Cited

Askins, R. A., Lynch, J. F. and Greenberg, R. 1990. Population declines in migratory birds in eastern North America. In Power, D. M. (ed.) Current Ornithology, Volume 7: 1-57. New York: Plenum Publishing.

Robbins, C. S., Sauer, J. R. Greenberg, R. S. and Droege, S. 1989. Population declines in North American birds that migrate to the neotropics. Proc. Natl. Acad. Sci. 86: 7658-7662.