Bird Migration & Wintering
Most species identified as SGCN spend a significant portion of their life cycle in Michigan. A focus on these resident species would benefit a large proportion of Michigan's wildlife, but it would not address the needs of all wildlife found in the State over the course of a year.
Migration Routes and Stopover Sites
Migratory birds which pass through Michigan and the Great Lakes without breeding are largely overlooked in the set of SGCN, but they constitute a significant group of wildlife dependent on Michigan's landscape features for their continued survival. Important migratory pathways and habitat along Great Lakes shorelines have been identified at more than 60 sites (Scharf 1971). Table 1 identifies several recognized migratory paths and stopover sites with estimates of their use by birds. One site, Pointe Mouillee, has been designated part of the Western Hemisphere Shorebird Reserve Network.
Table 1. Partial list of stopover and migration sites in Michigan
|Keweenaw Peninsula||1992||Raptors (migration)||16,000||Spring|
|Erie Metro Park||2004||Raptors (migration)||261,572||Fall|
|Baker Sanctuary||2003||Sandhill Cranes (staging)||5,328||Fall|
|Nayanquing Point||Tundra Swans||~5,000||Spring|
Recent surveys have reconfirmed significant migratory bird use of Great Lakes islands. One-hundred eight different bird species were observed during spring migration on Beaver, Garden and Bois Blanc islands (Penskar et al. 2000). Islands may be important to migrants for three reasons: nocturnal migrants find themselves over open water and at dawn and seek the nearest land; islands act as northward extensions of mainland migration routes; and islands are the intended destination of migratory species that regularly nest on them (Scharf 1996). A recent study confirms that migrating birds do tend to congregate along Great Lakes shoreline areas because they provide the first opportunities to land upon daybreak (Diehl et al. 2003).
Migration accounts for the majority of annual adult mortality in land birds (Sillett and Holmes 2002). This biannual journey is the most energetically expensive process in a bird's life. Loss of stopover sites or modification of landscapes along important routes can have effects at a regional scale. One threat is the simple lack of knowledge of vital stopover sites and migratory pathways. Importance of these sites is not just defined by geographic locations, but also by their geologic and vegetative characteristics. A study using NEXRAD weather radar data to identify migratory routes and stopover sites found that important stopover habitat consists of sites with a diversity of vegetative types (Botner et al. 1992).
A potential mortality threat during migration is placement of obstructions along major migratory routes. Studies have identified collision with both tall buildings and communication towers as potentially significant causes of migratory bird mortality. An estimated 5,000 communication towers are constructed in the U.S. each year (Shire et al. 2000). In Michigan, 75% of species identified as Birds of Conservation Concern by the USFWS have been found dead under communication towers. Additionally, threats posed by wind farms may need to be considered if construction of these structures increases significantly in Michigan.
Although not readily apparent, Michigan is a wintering site for some northern nesting bird species. Regular winter residents include Snowy Owls, Great Gray Owls, Northern Shrikes and Oldsquaws which migrate from northern landscapes (Mcpeek and Adams 1994). Winter Bald Eagle surveys coordinated by the Michigan Department of Natural Resources have identified several wintering areas along the Great Lakes. These sites tend to be open water areas maintained by natural flow, warm water discharge, or open water fissures in ice covering lakes. Occasionally, these sites have been reported to host more than a dozen eagles at any one time. Protection of features that support these species is important.
Conservation Needs to Address bird migration and wintering issues:
Land & Water Protection
- Initiate projects that protect known sites or ensure sites nearby are sustained
- Protect important migratory routes and stopover sites
Land, Water & Species Management
- Use best management practices for construction and management of human-made tall structures to help reduce mortality
- Assess value of management practices affecting migratory routes or stopovers
- Develop and implement management practices that ensure wintering bird habitat remains
Education & Awareness
- Provide information on important migration routes and stopover sites to land-planning agencies and organizations
Research, Surveys & Monitoring
- Identify characteristics and processes that make routes or stopovers attractive to migratory birds
- Develop and test best management practices for construction and management of human-made tall structures to help reduce mortality
- Conduct research to determine which management practices may affect migratory routes or stopovers
- Conduct research to determine relationships between winter resident birds and landscape features
- Identify important migratory routes and stopover sites and protect these areas
- Monitor migratory-bird use of Great Lakes features, both as stopover and as staging areas
- Conduct research to assess effects on wildlife populations due to mortality from collisions with fixed (e.g., communication towers, wind turbines) and mobile objects (e.g., airplanes)
- Conduct research to examine the effect of light pollution on wildlife movement patterns