Ruby-Throated Hummingbird Fall Migration

The fall migration is a journey south back to Mexico and Central America and starts when the abundance of insects starts to dwindle with along with colder temperatures.

Ruby-throated Hummingbirds aren't well adapted to cold temperatures — they have a tough time below the mid-20s F, and don't enter torpor as regularly as their western cousins to conserve energy. To avoid the cold and the scarcity of food when flowers stop blooming and insects stop flying, they go south.

In Wisconsin, males are the first to migrate south by the end of August. The females and first-year hatchlings will hang around longer in Wisconsin. Surprisingly, a couple have been recorded in December, although most will be gone by mid-October

  Hummingbirds, In General

Each hummingbird species has its own migration strategy, and it's incorrect to think of "hummingbirds" as a single type of animal, all alike. This article will discuss Ruby-throated migration, because it's likely that more people see that species than all the others in North America combined, and its dynamics are similar to other species, although the dates and locations vary.

Although hummingbird migration is not well documented by large numbers of banding records, we do know a few facts, and we can draw logical inferences about some of the unknown areas. ("banding" means trapping a bird and wrapping a tiny numbered strip of aluminum around one leg).

  Why Migrate?

As with most of our migratory birds, hummingbirds apparently evolved to their present forms during the last ice age. They were (and largely still are) tropical birds, but as the great ice sheets retreated from North America, they gradually expanded their ranges to exploit rich temperate food resources and nesting space, filling unoccupied niches in the U.S and southern Canada while evading intense competition in the tropics.

Some songbird species have adapted completely to our variable North American climates, in part by becoming vegetarians in winter, and don't migrate. But hummingbirds are carnivores (nectar is just the fuel to power their fly-catching activity), and depend on insects that are not abundant in subfreezing weather, so most of them must retreat back "home" to Central America in the winter or risk starvation.

A few Ruby-throated remain along the Gulf coast each winter instead of continuing to Central America, perhaps because they are too old or sick to make another trans-Gulf flight or too young (from very late nests) to have had time to grow fat and strong enough to migrate; their survival chances depend on the severity of each particular winter, and many perish in unusually cold years. Another small population winters in the Outer Banks of North Carolina.

  Fall Migration Triggers

Although there are differing views in the birding community as to what triggers the start of fall migration, it is generally thought that hummingbirds sense changes in daylight duration, and declining numbers of flowers, nectar and insects.

Instinct, their internal biological calendar, and cooling weather conditions also play a role in making the decision to migrate.

  Who Is At My Feeder In December?

Those involved with banding these rare migrant hummingbirds in late October through January refer to these birds at “winter hummingbirds.” In most cases where these winter hummingbirds are observed in Wisconsin, rescue efforts are not warranted.

In fact, such measures can significantly interfere with the migration of an otherwise healthy bird. In addition, once one of these hummingbirds has found its way to a hummingbird feeder late in the season, removal of that feeder will not necessarily “force the bird to migrate” and can serve as a detriment to the bird’s survival.

For a late season hummingbird that finds its way to a feeder, that feeder provides carbohydrates for an energy kick. However, protein is also an important dietary component which these winter hummingbirds find by gleaning pine trees and foliage for midges and other cold-hardy insects.

A hummingbird's decision to migrate is multi-factorial and triggered by a variety of factors including hormones, weather, the bird’s overall condition, and food availability.

  Making The Trip

Ruby-throated hummingbirds aren't well adapted to cold temperatures — they have a tough time below the mid-20s ° (F), and don't enter torpor as regularly as their western cousins to conserve energy.

To avoid the cold and the scarcity of food when flowers stop blooming and insects stop flying, they go south. Some adult males start migrating south as early as mid-July, but the peak of southward migration for this species is late August and early September. By mid-September, essentially all of the Ruby-throated hummingbirds at feeders are migrating through from farther north, and not the same individuals seen in the summer. This is difficult to see, since they all look alike, but has been proven by banding studies.

The number of birds migrating south may be twice that of the northward trip, since it includes all immature birds that hatched during the summer, as well as surviving adults. For a hummer that just hatched, there's no memory of past migrations, only an urge to put on a lot of weight and fly in a particular direction for a certain amount of time, then look for a good place to spend the winter.

Once a Ruby-throated hummingbird learns such a route, a bird may retrace it every year as long as it lives. The initial urge is triggered by the shortening length of sunlight as autumn approaches, and has nothing to do with temperature or the availability of food. In fact, hummingbirds migrate south at the time of greatest food abundance. When the bird is fat enough, it migrates.

  How Fast Do They Fly?

Research indicates a hummingbird normally can travel as many as 23 miles in one day. At that rate it can take several weeks to reach their wintering grounds from summer breeding grounds in the northern U.S. or southern Canada. But in certain circumstances, like the journey over the Gulf of Mexico, they can fly for more extended lengths of time, like 22 hours, nonstop!

The distance a hummingbird flies in one day is determined by the species, terrain, wind velocity, and food sources along the way. The average hummingbird flies 25 miles per hour. Ruby-throated hummingbirds fly by day when sources of nectar are the most abundant. They also fly low, which allows the birds to see, and stop at, food supplies along the way.

Ruby-throated hummingbird flies across the Gulf of Mexico none-stop using the wind to their advantage, increasing their speed and shortening the time it takes to cross over the water. Hummingbird banders have shown that this journey across the Gulf generally takes about 22 hours. This tiny bird flies non-stop for 22 hours across the water.