Short link to this page: https://go.usa.gov/xwkf5
Bird Migration in the Florida Keys: Frequently Asked Questions
Are there bird watching organizations in the Florida Keys?
What about the migration of monarch butterflies?
Links to additional information
Migration is the periodic travel of an animal as it returns eventually to its original place of departure. Migration is often annual and is closely linked with the cyclic pattern of the seasons. It is most evident among birds, which have a highly efficient means for traveling swiftly over long distances. The migration of most birds is a yearly cycle.
Birds migrate in search of food and a suitable environment for reproduction. In the United States and Canada, most birds migrate south for the winter reaching as far south of South America. Not all birds migrate, some bird populations like Cardinals that reside in the southern United States stay in the same areas throughout the year. Other birds do short migrations, sometimes just moving from a higher to a lower elevation during the winter. Long-distance migrants reach Central and South America and include about 350 bird species in the United States.
There are many triggers that let birds know that it is time to head south for the winter or return home for the summer. Migration can be triggered by a combination of changes in day length, lower temperatures, changes in food supplies, and genetic predisposition. For centuries, people who have kept cage birds have noticed that the migratory species go through a period of restlessness each spring and fall, repeatedly fluttering toward one side of their cage.
Over 100 species of birds fly over the Florida Keys. Some use the island chain to take a break and recuperate forces before continuing in their journey. One of the species that crosses our shores is the tiny Northern Parula, a bird with a wingspan of only 6-7 inches. The Pectoral Sandpiper has an amazing range, residing in the summer as far north as Siberia and Alaska and wintering in South America!
What elevation?
Like a plane, birds start flying low and gradually ascend to higher heights. Many species fly at 2,000 to 5,000 feet. Key West radar estimates as birds are crossing the Keys suggest that they are flying at a height of about 3,000 to 5,000 feet. Long-distance migrants can reach up to 20,000 feet. The record for the highest flyer goes to a vulture! A Ruppell's Griffon, with a wingspan of 10 feet, was recorded flying at 37,900 feet when it was unfortunately sucked into a jet engine.
The number of birds migrating across the Florida Keys fluctuates during the migration season. Radar reflectivities observed in August were around 10-15 decibels relative to Z (dBZ), suggesting a rate of around 10,000 birds crossing per mile, per hour. Therefore, a conservative estimate along a 100 mile stretch of the Keys would suggest a million or more birds crossing per hour! However, reflectivity values increased during the peak migratory season in September and October, with a hyperbolic increase in the number of birds crossing based on values surpassing 20 dBZ, which gives us about 25,000 birds per mile, per hour. Millions of birds crossing the Keys seems like an exaggeration, but a recent study estimated that 4.7 billion birds migrate from the United States into the tropics every autumn.
Most birds migrate at night. The stars and the moon aid night-flying birds’ navigation. Free of daytime thermals, the atmosphere is more stable, making it easier to maintain a steady course, especially for smaller birds such as warblers that might fly as slowly as 15 miles per hour. Cooler nighttime temperatures also help keep hard-working birds from overheating. And for birds that frequently wind up on the menu of hawks, cats, and other daytime predators, flying under cover of darkness can be a lifesaver.
In North America, the birds that migrate do so in the late summer through the fall and in the late winter through the spring. Migrations generally follow a north-south pathway, although a few bird species – namely oceanic birds -- may migrate in a circular pattern. However, not all birds migrate at the same time. For example, wintering birds may begin heading south as early as late July in the northernmost latitudes. Birds in southern latitudes may decide to leave as late as October. Basically, birds begin migrating as the weather begins to get colder and the sun angle decreases.
Are there bird watching organizations for the Florida Keys?
Here are a few bird watching organizations:
Key West Botanical Garden Society
Florida Keys Audubon Society
Tropical Audubon Society
What about the migration of monarch butterflies?
The annual migration of North America’s monarch butterfly is a unique and amazing phenomenon. The monarch is the only butterfly known to make a two-way migration as birds do. Unlike other butterflies that can overwinter as larvae, pupae, or even as adults in some species, monarchs cannot survive the cold winters of northern climates. Using environmental cues, the monarchs know when it is time to travel south for the winter. Monarchs use a combination of air currents and thermals to travel long distances. Some fly as far as 3,000 miles to reach their winter home!
For more information on any of this material, please see the following sources/references:
All About Birds: Which Species is Which?
All About Birds: The Basics of Bird Migration: How, Why, and Where?
Audubon Magazine: Listening to Migrating Birds at Night May Help Ensure Their Safety
Weather.gov: Radar Reflectivity
Displays of Bird Movements on the WSR-88D: Patterns and Quantification, June 1998
EarthSky: Birds Flying South, How Many will Return?
Texas Parks and Wildlife: Bird Migration FAQ
U.S. Forest Service: Monarch Butterfly Migration and Overwintering
Follow us on Twitter
Follow us on Facebook
KEY RSS Feed
