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Seasonal Migrations Mean Changes for the Coastal Bays - November 26, 2017

All around the world and throughout all seasons, migration is seen in a wide variety of animals ranging from mammals and avians to fish, reptiles, and insects.  Migration is the movement of a species from one location to another at certain times of the year or during specific stages of their life cycles.  On the Eastern Shore and Coastal Bays, many species can be seen both migrating to and from the area. Animals migrate for a variety of different reasons such as traveling to a particular breeding ground, lack of food supply, or seasonal changes.

There are several types of migration based on differences in direction, timing, and purpose. Reproductive migration is the movement of species towards their breeding grounds. These grounds may be safer and more suitable to rear young in than the habitat required for mature adults. Altitudinal migration is the movement between high and low altitudes, like the top of a mountain to the valleys below. Many animals move from the colder, high altitudes to the lower, more moderate altitudes during winter months. Latitudinal migration is the movement of animals between north and south. Animals avoid seasonal extremes by moving to warmer latitudes during the winter and returning to cooler latitudes in the summer. All of these types of migration can also be considered seasonal migration; the movement of species that corresponds to the change in seasons.

Migrating animals face many obstacles throughout their journey. Many animals, such as migrating songbirds, build up huge fat reserves prior to their migration, as over the course of their migration, they can lose half of their body weight. Often, migrating animals will cover extreme distances in a small timeframe, leaving them exhausted. This leaves them vulnerable to other challenges such as predation, climate change, and habitat loss.

Some of the most prevalent migrating groups of animals on the Eastern Shore are vast flocks of songbirds, waterfowl, and occasionally birds of prey. During their winter migration, waterfowl use the Coastal Bays as either a resting point or final wintering location. Common Loons often overwinter in the Coastal Bays, with the juveniles remaining in their coastal wintering grounds for the first two years of their lives. In their third year, the juveniles migrate north again for breeding. The bufflehead, a species of diving duck, also spends winter in the Coastal Bays before journeying back north for nesting season in the spring. Tundra Swans fly south from the Arctic Circle, and can be seen wintering in the thousands on the Eastern Shore. The Chesapeake Bay region has one of the largest wintering populations of Tundra Swans in the country.

One species of shorebird that can be seen in the Coastal Bays during their return spring migration is the Red Knot. Red Knots have one of the longest yearly migrations of any bird species. They travel over 9,300 miles from their Artic breeding grounds to their wintering grounds in the southern tip of South America and then repeat the journey in the spring. The Delaware Bay serves as an important stopover site during the spring migration, where eggs of spawning horseshoe crabs provide food for the journey. In a single day, about 90 percent of the Northeastern subspecies’ population (the Rufa Red Knot) can be present in the bay.

Birds of prey such as owls occasionally migrate through the Coastal Bays throughout the fall and winter. Saw-whet owls begin their migration south from eastern Canada in late September to arrive in the Coastal Bays between late October and November. Their southward migration typically ends in early December and by early spring they begin their journey northward. Rarely, snowy owls will migrate through the Coastal Bays. Snowy owls typically reside yearlong in the Artic but will migrate south for reasons not fully understood. Some years only a small number of snowy owls will undergo migration while other years, large numbers of owls will migrate south in what is known as a mega-irruption. The winter of 2013-2014 saw one of these mega-irruptions: snowy owls were reported as far south as Florida and Bermuda. Project SNOWstorm, a volunteer Snowy Owl-tracking organization, predicts that a large irruption may occur this coming winter. 

Unlike owls, ospreys migrate from their northern breeding grounds in the Coastal Bays to their wintering grounds in Central and South America.  Ospreys mate for life, but upon migration, they journey alone. The mates will not meet again until returning to their nest in the spring for mating.

Similar to birds, fish also migrate south to find more suitable temperatures and food availability. Bluefish and weakfish share similar migration habits, migrating south to warmer waters between North Carolina and Florida. Upon the return of spring, they will return north to the Chesapeake and Coastal Bays, and even as far north as Maine. Migrating schools of Bluefish can cover tens of square miles of ocean. Atlantic menhaden are some of the most abundant finfish species in the coastal Atlantic waters. They will begin forming schools throughout spring and summer and by autumn these schools will migrate to the deeper waters off of North Carolina. The fishing favorite, striped bass, also undergoes seasonal migration. They spend the summer in the Chesapeake and Coastal Bays, and then migrate to warmer waters off North Carolina in the winter. Some juveniles and adult males will forgo migration and overwinter in the bays in deep channels.

Seasonal migrations create a great deal of change in the Coastal Bays. With the arrivals and departures of so many species in our Coastal Bays, it is an ideal time to see our winter visitors.

Phillips is the Environmental Scientist for the Maryland Coastal Bays Program. 



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