Monitoring Bird Populations on Three Great Lakes National Forests: 1991-1996

Abstract

A habitat specific bird monitoring program was established on the Chippewa and Superior National Forests in 1991 and the Chequamegon National Forest in 1992. The program was designed to assess annual differences in bird relative abundances and to eventually distinguish between larger-scale trends and small-scale shifts in abundance. Data collected through 1996 have provided information on annual variation and trends over time for individual species and community parameters and relative abundance within representative cover types on the Forests. A total of 19 species (all national forests combined) had significant linear trends (P less than or equal to 0.05 for linear contrast) from 1991 or 1992 to 1996. Fourteen out of 19 (74%) increased and five (26%) decreased in abundance. In the Chequamegon, 10 out of 13 species (77%) increased from 1992 - 1996 and three species (23 % ) decreased during that time period. Six out of nine species ( 67 % ) increased from 1991 - 1996 in the Chippewa and nine species (33%) decreased. In the Superior, five species (83%) increased over the period of the monitoring and one species (17%) decreased from 1991 - 1996. Four species had the same significant linear trends in two out of three of the national forests: the Yellow-bellied Sapsucker increased in the Chequamegon and Superior National Forests; the Blue Jay increased in the Chequamegon and Chippewa National Forests; the Ovenbird increased in the Chippewa and Superior National Forests; and the Purple Finch decreased in the Chippewa and Superior National Forest. One species, the Hermit Thrush, had the same increasing trend in all three national forests. A change in methodology in 1994 (sampling within a limited radius vs an unlimited radius) is likely responsible for increases in 10 out of 19 (53%) species. A single explanation can not be offered for the _significant trends in the other species. Results from the monitoring can be used to aid forest managers by providing information on bird/habitat associations within forest cover types. Trends from long-term monitoring will be useful in resolving potential problems within a national forest or to support conclusions that a problem does not exist. Cumulative number of species that have a total number of observations of at least 25 (rare species) increases with each year of monitoring. Based on power analysis, a sufficient sampling regime is in place to detect reasonable changes in abundance for many forest birds, including many neotropical migrants.