American White PelicansPurple PetuniasSandhill CraneHorse's EyeAmerican BisonSparring American ElksAurora Borealis

by Bob Dean

In the natural world everything is in constant motion. Nowhere is this as visible as the migration of wildlife from one place to another. The avian members of the animal kingdom don’t have a lock on migration but they do have the most visible for people all over the planet.

Birds migrate for one basic reason, to survive as a species. The driving factors are normally food supply and nesting territory. Migration normally takes place between the nesting and the non breeding season. The terms used here (nesting and non breeding) are specially chosen to allow for seasonal and geographic variations.

There are many different types of migration, depending on the time, direction, distance covered and magnitude of the behavior.

Complete migration is the type we think of generally when discussing migration. This term is applied when all members of a population leave a nesting area during the non breeding season. There is typically no overlap of nesting and non breeding territory. Consider the example of the rough-legged hawk that nest in the far north and winters in the lower forty eight states.

Partial migration is applicable when some individuals remain in the nesting area during the non breeding season while others leave for another area. Red tail hawks are representative of this behavior as some migrate while others remain in the nesting area. The result is an overlap of typical nesting territory with typical non breeding season territory.

Differential migration refers to differences in distance or seasonal movement of portions of a species. This is normally divided by age or sex. The herring gull nests in the Great Lakes area and migrates to one degree or another to the eastern seaboard. The first year birds tend to move the farthest, sometimes deep into the south. The second and third year birds don’t go quite as far south while the adults (four years and older) remain much further north, even in the nesting territory. American kestrels demonstrate differential migration in that the males tend to remain closer to the nesting territory while the females migrate greater distances. The reasons for this behavior vary. The herring gull migration pattern is most likely due to social dominance where the younger, less aggressive birds move away from the more aggressive, older birds. In the case of the kestrel, the males remain close to the nesting territory to enhance their chances of reclaiming the best sites when nesting season returns.

Another type of migratory behavior is irruptive migration. This movement is irregular and normally driven by food or weather conditions which don’t follow a normal seasonal pattern.

To assign a particular migration type to any population of birds is difficult because some sub species or particular groups may not do what others do. Natural selection has programmed the behavior of these groups so survival and reproductive chances are maximized.

The frame of reference for North America is typically north-south movement. This is generally referred to as latitudinal migration. Blue wing teal nest in the North Dakota pothole country and winter in the marshes of Louisiana, a typical north-south migration. Other species migrate in an east-west pattern, such as the white winged scoters that nest in Alaska and winters in western Ontario. This east-west movement is called longitudinal migration. This pattern is very much food source driven.

There are birds migrating from one elevation to another to achieve the climate and food requirements they need. This behavior can lead to significantly different migration routes, depending on the location. As an example, a subspecies of dark eyed junco, nesting in the mountains of West Virginia, migrates to the lowlands in winter. This is a journey of twenty to thirty miles. A very similar junco, nesting in the forests of northern Maine, may migrate over a thousand miles to achieve the same results.

If we move away from the common migratory behavior common in North America, we see many examples of very different behavior. In the southern hemisphere there are mirror image north-south journeys, called austral migration. Some of these migrants will actually cross the equator and show up in the north as rare bird alert material. One of the major differentiators between the hemispheres, leading to vast population differences, is the polar land mass. In the northern arctic there is substantial nesting habitat in the higher latitudes, yielding a large migratory population. In the south, the equivalent area is open water or the barren land mass of Antarctica.

The southern hemisphere does have it large bird populations, and these groups do have their migratory behavior patterns. The populations are much larger in the tropical and near tropical areas of Australia and Africa.

Seasonal migration in the southern hemisphere tends to follow the wet season, as the moisture tends to generate the food supply (particularly insects, the bottom of the avian food chain).

There is an aspect to migration, besides the general knowledge, interesting to the nature photographer. The fact that migrations can take significant time and energy means that birds need to stop and rest along the way. Combine this with the regularity of travel and the large numbers of migrants, the opportunity for photography can be incredible.

Stopover locations are the best places to get images of birds not living in your area on a year around basis. These stopover locations are essential to successful migration and breeding. Birds use these stopovers to gain and replenish fat used to provide energy during long flights. The rest breaks can be as short as a few hours or can last many weeks. Sand hill cranes from the Bosque del Apache refuge in New Mexico will spend four to six weeks in the San Luis Valley of Colorado on their northward migration to Gray’ Lake NWR in Idaho. This is a classic example of a great opportunity for bird photography.

Waterfowl spring migration is very different from most other birds. Ducks and geese tend to eat their way to their destination. These birds travel as part of very large flocks and will stay at a location as long as the food source is viable. When the nourishment is gone, the birds will move on to the next location.

The knowledge of tactics used by birds during migration, as well as their routes, is very beneficial to the nature photographer. The tactics are varied, ranging from the hawk family’s tendency to ride thermals to a high altitude and then soar, to the ducks rapid wing beat with frequent stops. Song birds tend to fly at night and roost during daylight hours at their stopover locations, while waterfowl and raptors fly during the day. Song birds also tend to migrate after a weather front has pasted so they may take advantage of the wind direction.

The knowledge of your subject is critical to the success of your photo work. Study the migration habits of birds coming through your area or check with local bird experts. There are two chances a year to catch these avian vagabonds, so don’t be caught seeing the north end of the last south bound migrant.