Talking Minnesota’s migratory birds with U of M
World Migratory Bird Day is celebrated annually on the second Saturday in May and October to raise awareness of migratory birds and their habitats. This year’s first observance is May 13.
Avian Ecologist Steve Kolbe with the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth answers questions about migratory bird populations in Minnesota, their migration routes and patterns, and the condition of their habitats.
Q. What species of migratory birds are commonly found in Minnesota and where?
Kolbe: Minnesota contains varied habitats — from grasslands in the west and bottomland deciduous forests in the southeast to boreal forests in the north. The combination of these habitats in a single state means that Minnesota is an extremely biodiverse state during migration (and the summer breeding season)! Additionally, the harsh winter conditions we experience in Minnesota mean the majority of birds migrate away from the state each fall. Combine these two factors and we see massive numbers of birds of a wide range of species leaving and returning to the state each year. Minnesota is also fortunate because it’s the end of the migratory journey for a wide range of species that spend the summer in the state. Many southern states see species such as warblers only during spring and fall migration, but in Minnesota we get to enjoy them all summer long!
One of the first signs of spring is the huge flocks of geese and waterfowl that arrive as soon as open water is available. Eagles and hawks migrate back in large numbers throughout March and April. These birds are soon accompanied by the arrival of short-distance migrants such as American Robins, Red-winged Blackbirds and Eastern Bluebirds that have spent the winter in the southern United States. After the weather warms and leaves start to appear on trees, long-distance migrants — species that have spent the winter in Central or South America — such as orioles, tanagers, grosbeaks, and warblers begin to arrive and prepare for the breeding season. Birdwatchers are able to see well over 100 species of birds in a morning during this peak spring migration season along migratory corridors such as the Minnesota and Mississippi Rivers and Lake Superior.
In the fall, this pattern is reversed. Long-distance migrants leave as early as August, and short-distance migrants trickle south throughout September and early October. Eagle and hawk numbers peak in October as the weather starts to turn, and finally the small number of hardy migratory species, such as finches, that spend the winter in Minnesota arrive in November and December.
Q. What is the typical migration route for these migratory birds? And how do they get there?
Kolbe: Migration routes vary depending on the species and the location of their non-breeding grounds. For most species, the well-worn concept of migratory flyways is a gross oversimplification. Spring migration routes that end in places as distant as Alaska and Hudson Bay cross in Minnesota. Similarly, birds that winter on the Gulf of Mexico, the Atlantic Coast, and Central and South America all pass through the state in the fall.
In general, most spring migrants fly as directly as possible to their breeding grounds in order to occupy the best territories as quickly as possible. In the fall, birds will generally take a more southeasterly route at a more leisurely pace to get to their wintering grounds.
The majority of bird species migrate at night and use multiple cues to help them navigate in darkness, including magnetic and polarized light fields and the stars. During a typical night of migration, an individual bird likely tries to travel as far as it can, given its energy stores and the flying conditions. Some species, such as Tundra Swans and Sandhill Cranes, are dependent on very specific habitats during migration and will follow traditional migratory routes and stop at the exact same areas each year. Because these species migrate in groups — often including adults and their offspring — knowledge of these prime stopover areas is passed down to future generations. Species that migrate during the day are much more likely to use geographic landmarks like river valleys or lake shorelines as landmarks and to use soaring flight, which utilizes updrafts off ridgelines or thermals of rising air produced by the uneven heating of the Earth’s surface.
Q. How and what changes in habitats impact migratory birds and their migratory behavior?
Kolbe: Of the approximately 315 species that are regularly detected in Minnesota, nearly 250 breed in the state. Quality habitat that provides food and shelter is critical for birds during migration and for breeding activities. In terms of migration, the majority of birds are relatively flexible and use any available stopover habitat that they can find. Some bird species stop for a day, or even a few hours, during which time they try to regain fat stores used to migrate by eating as much as possible. Other birds stay for much longer to refuel or wait for nice weather before making another migratory flight. For all species, habitat quantity and quality are the most pressing concerns. If a bird is unable to find enough suitable stopover habitat, it will be unable to refuel and make another migratory leap. Because human presence on the landscape in much of the state is high, we must make sure that as much natural habitat is saved as possible. Additionally, if a bird stops over at a site of lower quality, such as a site filled with invasive plant species, it may take much longer to gain enough nutrients to prepare for the next leg of the journey. Ensuring high quality stopover and breeding habitat is available for all birds is a top priority for bird conservation!
Q. How do migratory birds respond to extreme weather events?
Kolbe: Birds have an amazing ability to respond to changes in the weather. In the spring, birds are incentivized by the choice of good breeding territories to arrive on the breeding grounds as soon as it is possible for them to find food and survive. However, when unexpected weather such as the snow and ice storms we experience in the spring occur, birds will often reverse course and migrate south until conditions improve before heading farther north. Residents along the north shore of Lake Superior likely saw a dramatic example of this in mid-April of this year: thousands of American Robins, Dark-eyed Juncos and other short-distance migrants that had migrated into northern Minnesota and beyond during the brief warm-up flooded back south down the shore when snow, ice and cold northwesterly winds descended a few days later. These birds will likely wait for warmer (and less snowy) weather to arrive before continuing their northward journey.
Q. What are you doing to advance research on Minnesota’s migratory birds?
Kolbe: The Avian Ecology Lab at the Natural Resources Research Institute is on the cutting edge of the study of migratory bird species in Minnesota. We specialize in using the latest technology to answer questions about how, where, when, and why birds migrate. For example, along with collaborators across North America, we have placed geolocators and GPS tags on Common Terns, American Woodcock and Golden-winged Warblers in order to understand migration routes and where they spend the winter.
Our group is also heavily involved in a global effort called the Motus Wildlife Tracking System. The goal of this project is to use automated telemetry to track the migratory movements of birds that are too small to be equipped with more sophisticated GPS tracking devices. Our group currently has nine stations along the north and south shore of Lake Superior. These stations have detected birds that were tagged as far away as Maryland and British Columbia! These new technologies have helped us to start to unravel the mysteries of migration and help inform conservation of Minnesota's birds.
Steve Kolbe, M.S., is an avian ecologist and staff member of the Avian Ecology Lab at the Natural Resources Research Institute. He has a special interest in bird migration and movement, testing novel survey methodologies and acoustic identification. Kolbe’s research focuses on the ways in which birds use their environment at varying scales throughout the annual cycle. The Avian Ecology Lab focuses on developing economically sustainable conservation strategies and land management guidelines to preserve and enhance the species diversity of Minnesota bird populations and to protect species in need of greatest conservation.
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About the Natural Resources Research Institute
As part of the University of Minnesota system research enterprise, the Natural Resources Research Institute at the University of Minnesota Duluth employs over 140 scientists, engineers, technicians, staff and students in two industrial research facilities. Through collaborative partnerships, NRRI delivers the innovative tools and solutions needed to utilize and sustain Minnesota’s valuable natural resources.
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