Warner, D.W. and A.R. Weisbrod. 1985. Bird migration in the St. Croix River valley: use of fragmented habitats by migratory birds. Final report submitted to the Minnesota Department of Natural Resources. 35 pp.
This report describes our filed studies and examples of the preliminary findings of this research on birds and vegetation in several habitats on the Belwin Outdoor Education Laboratory site and adjacent properties in Afton, Washington County, MN. The primary purpose of the study was to learn whether these small fragmented habitat units that were inadequate for successful breeding by long distance migrants were also inadequate for use as stopover sites for replenishment of fat reserves during migration. Our objectives included: 1) Determine at what level of fragmentation the dwindling natural habitats of the region begin to adversely affect the migrating birds that use these sites for refueling and the migratory birds that breed there and 2) Begin to construct a database of information on birds, bird migration, breeding bird species, the habitat preferences of each species, the kinds of plants and their relative numbers that make up the various habitats, etc. The database will be computerized for Belwin Outdoor Education Library.
Spring migrants captured totalled 2,600 individuals of 72 species. Late summer (August) and early fall (September) netting resulted in 3,175 individuals of 78 species. Total recaptures and birds captured in special nets bring the total number of birds handled to approximately 7,500. Examination of the tables shows the different peak periods of migration during certain periods. Note that in some species, about 90% of the individuals passed through Belwin in about 48 hours in spring migration (May). In fall these peak periods are not so defined, largely due to the longer, more erratic migration of the young of the year. The breeding bird censuses resulted in figures that basically show breeding birds are not very numerous in either species or numbers of individuals.