Understanding Fall Migration
Adapted by Marla Mertz, Marion County Conservation, and Linette Bernard, Feathers & Ink, from Migration Mysteries: Disappearing Neotropicals, Dr. Jim Pease, Emeritus, Extension Wildlife Specialist (ISU-Retired)
Migration is the movement of animals from one place to another. We are all familiar with the migration of birds like the American robin that arrives in our backyards with the coming of spring. These birds have returned from the places where they spend the winter, to our area where they will nest and raise young birds.
People have been fascinated with this annual migration of birds for thousands of years. Aristotle was an ancient philosopher who wrote about the wintering habits of birds 3,000 years ago. He noticed that some birds traveled to warmer places to spend the winter. He also mistakenly believed that some birds like swallows hibernated to survive the harsh winter weather. This theory persisted for 2,000 years!
Today, we know that birds do not hibernate. But it does show how long people have been trying to understand the disappearance of many birds from northern climates in the fall. So what do we know now about migration? Where do the birds go? How? Why? Today, scientists know far more now about migration than they did even 25 years ago.
When you see flocks of birds flying overhead in the fall, they usually are flying south toward their wintering grounds. How far south they go depends on the type, or species of bird. Some birds travel farther than others. For example, in some species females and young birds fly farther south than males. Remember that some insects also migrate during the year.
- NOVA: The Incredible Journey of the Butterflies on YouTube, Aired 30 November 2011 on PBS. (52:17 in length)
- Learn more about bird migration from the Cornell Lab of Ornithology: All About Birds: Migration
- Audubon: Online Guide to North American Birds
- Weekly forecasts of birds, maps and migration
- Audubon Magazine - Fall Migration Hot Spots (Published July-August 2009)
The largest group of birds that we see during migrations are called neotropical migrants. They got this name because these species of birds migrate in the fall all the way to Mexico, the Caribbean islands, and other Central American and South American countries in the tropics. This means these birds fly thousands of miles every fall and spring. About 300 of the 650 bird species that nest in North America are neotropical migrants. They include warblers, vireos, orioles, hummingbirds, swallows, swifts, shorebirds, and some birds of prey.
When birds migrate (and how far they migrate) is closely tied to why they migrate in the first place. Primarily, birds go south in the winter to find food. However, these birds need more room and even more food during the breeding season when they have a nest of young ones to feed. To solve this problem, the birds migrate north for the summer. As a result, when their bodies become ready to breed every spring birds know it is time to migrate north. In the fall, their body puts on fat and signals that it is time to begin their long journey south. Actual migration begins when the birds are triggered by some other stimulus, such as a change in temperature or weather. How do we know where birds travel to as cold weather approaches?
Transmitter technology is used by wildlife biologists and researchers to track movement. What do researchers hope to learn by using the various tracking transmitters available for use with wildlife? That question varies by research project, below are a few:
South Dakota Game Fish and Parks
Osprey recovery in SE South Dakota used platform telemetry transmitters (PTTs) to track long-distance movements. South Dakota added this feature to their recovery project (which ran from 2003-2010) to learn more about migration movements and wintering habits of reintroduced birds. Ospreys are 3-4 years old before their first successful nesting. Young birds remain in the wintering area until they are approximately 22 months old before returning to a potential nesting area. These are the questions researchers were hoping to answer with telemetry data:
- Document the timing, distance, and routes of migration for juvenile ospreys hacked from selected sites in South Dakota.
- Identify wintering areas and arrival and departure dates.
- Evaluate characteristics of the migration routes and wintering areas and attempt to identify potential threats to the ospreys based on this evaluation.
Sixteen ospreys were fitted for a backpack harness with transmitter and provided information on when migration from the release area in South Dakota began, the rate of migration, distances traveled, migration routes, and wintering areas. Unfortunately, none of the PTTs transmitted long enough (≥ 22 months) for us to document the return of any of the birds to possible nesting areas.
From the final SDGFP report for the osprey recovery project:
Satellite telemetry has shown that the young South Dakota ospreys, migrating to wintering grounds for the first time, generally migrated in a southeasterly direction to the Gulf of Mexico. Upon reaching the Gulf, however, the ospreys varied in their selection of wintering areas and how they reached those areas. While the young ospreys tend to follow the Missouri and Mississippi River drainages to the Gulf of Mexico during migration, the speed at which they can migrate allows them to cross large stretches of land with little water and large bodies of water with few places to perch and rest. There was considerable variation (9 to ≥70 days) in the time it took for ospreys to reach their selected wintering areas from the release area. Those ospreys that took 25-70 days to reach their wintering area exhibited migration stops of up to 44 days within the continental United States. These birds appeared to linger in areas (e.g., streams, ponds, lakes, and reservoirs) along the migration route that likely provided an abundance of fish to eat.
See more SD osprey recover at South Dakota Game Fish and Parks website.
Reducing the risk of osprey collisions with aircraft was a Department of Defense initiated research project. The goal of this research project (2006-2007) is to incorporate satellite telemetry technologies and geo-spatial referencing to quantify bird-strike risk of migrating and breeding osprey from the Mid-Atlantic Chesapeake Bay Region. The hope of this project was to gain better understanding of osprey breeding season and migration movements to reduce or even eliminate osprey airstrike / collisions. Check out the this compilation of information about the Osprey BASH Project (opens as PDF).
American White Pelicans travel up the Mississippi Flyway to Minnesota from wintering grounds in the Gulf of Mexico each spring. Two years after the BP oil spill in the gulf (began April 2010), researchers for the Minnesota Department of Natural Resources discovered pollutants from the spill in the eggs of pelicans nesting in western Minnesota. This included evidence of petroleum compounds and the chemical dispersant used to clean up the oil.
Approximately 20% of the world's breeding population of White Pelicans is found in Minnesota, and Audubon Minnesota has identified the striking birds as a "Stewardship Species" and made them the focus of special conservation efforts. In May 2012, a team from Audubon Minnesota, North Dakota State University, and the Minnesota Department of Natural Resources Nongame program fitted five adult pelicans with satellite-linked GPS tracking units. These units transmit hourly readings on the birds' locations, providing new insights into where they are foraging in the summer, their migration strategies, and how they use the gulf during the winter. This will help us learn more about the threats they encounter along the way, including risks posed by oil and other pollutants in the gulf and elsewhere. Minnesota Audubon has telemetry location map that display the routes of all four birds -- check it out here. As of March 2014, only one transmitter was still giving signal (P197). The transmitter data is part of a multi-year research project looking at the long-term impacts of the oil spill on wildlife that spend part of their year in Minnesota.
Craighead Beringia South is a wildlife research and education institute dedicated to conserving the natural environment that is located in the Jackson Hole Valley in Wyoming. Many raptors call the Jackson Valley, Grand Teton or Yellowstone National Park home in the summer, these same raptors travel south every fall. Identifying key migratory routes and wintering ranges is a vital piece to long-term conservation efforts. Threats along migration corridors, stop-over sites, and wintering areas can negatively impact these raptors. As part of several different projects, Craighead Beingia South has been documenting migration routes of ospreys, rough-legged hawks, golden eagles, red-tailed hawks, and bald eagles.
- Visit their website to read about telemetry research projects.
Project SNOWstorm is a group of dedicated scientists and organizations that wanted to capture as much data as possible during the 2013-14 snowy owl irruption that happened across Minnesota to New England. This group is wanting to learn how the modern world is impacting the snowy owl, both in their breeding habitat of the Arctic, but also during southern migration, what the snowy owl migration patterns look like from a local and a regional / landscape level.
- Learn more about the research project and Project SNOWstorm!
Flyways is a collaborative project of waterfowl managers across North America. A current project shows USFWS waterfowl biologists tracking movement of common and roseate terns and oystercatchers along Cape Cod and the islands of Massachusetts. Read more here.
Young Songbirds: Lazy Travelers or Clever Learners?
A researcher at York University in Canada has used backpack geolocator transmitters to track the spring migration of juvenile wood thrush. The wood thrush population is steadily declining and learning why juveniles arrive at the breeding grounds later than adults and where their stopover sites are may help unravel this mystery. Read the story here in Audubon Magazine.
Hawk Mountain Broad-winged Hawk Study
Follow along and track the amazing journey of the broad-winged hawk from space using satellite telemetry technology, and trace the movements of this long-distance migrant from Pennsylvania to Central and South America, and back. This study marks the first time a telemetry unit has ever been placed on a juvenile broad-wing. Through this study, Hawk Mountain researchers have a goal to learn more about the Broad-winged Hawk and its ecology during the breeding, migration and wintering periods in order to protect this secretive yet common woodland raptor, and to conserve its amazing migration for future generations.