Blog # 252 Osprey Spring Migration Routes

Juvenile Osprey eating a brown bullhead at Stewart Park, courtesy of Cindy and Karel Sedlacek. 

Spring is the time for new beginnings for all. For birds, this new beginning means it’s  time to build nests and refurbish old ones. It is a time of growing handsome new  breeding feathers as well as performing vital courtship behaviors to catch the eye of  passing mates. It is the time to lay eggs and raise a new brood. But before any of that  can happen, migratory birds must journey from their winter grounds back to their  breeding homes. Fall migrations can be long, drawn out affairs, but time is of the  essence when it comes to spring migration. In Ospreys, both males and females do all  they can to minimize the time spent on spring migration to ensure a timely arrival on the  breeding grounds to establish a nest or defend their existing nest. 

Ospreys employ different spatial and temporal migration strategies in spring versus fall.  A migration strategy is defined as ‘‘the set of rules that determine the total process of  migration, incorporating periods of both flight and energy accumulation/stopover.’’ The 

strategy of an Osprey’s spring migration, including periods of both flight and feeding  stopovers, is very different than that of the fall migration.  

Traditional osprey migration routes in North America differ by region as shown in the  maps below. 

Spring Migration of East Coast Ospreys. 

East coast Ospreys make a Caribbean crossing by island hopping from South America  to Florida. They continue north hugging the Atlantic coast and the Appalachian  Mountain chain to New York and New England.

Midwestern Osprey Migration Route. 

Midwestern Osprey either make a similar island-hopping Caribbean crossing as do the  East coast Osprey population or head north inland through Central America and Mexico  before radiating throughout the Midwest. Ospreys on the west coast migrate from South  America directly to Central America to Mexico before heading to points north along the  west coast.

Spring Migration route of West coast ospreys. 

Departure and arrival dates during migration vary with the region. East-coast Ospreys  leave their wintering grounds and arrive on their breeding areas earlier than their  Midwestern and Western counterparts. East-coast Osprey nesting sites are primarily  coastal near waters that rarely freeze, allowing early returning Ospreys more opportunity to forage than their counterparts inland and in the Midwest, which have to  wait for frozen inland lakes and rivers to thaw.  

Getting an early start to breeding is strongly correlated with fledgling success in  Ospreys. Great selection pressures are exerted on Ospreys to return as soon as  possible to their nests to begin breeding. Males and females arrive in the area at about  the same time, but males often appear at the nest first. Additionally, both male and  female Ospreys show great nest site fidelity and are under pressure to arrive at those  sites early enough to defend them from unpaired marauding Ospreys. In saturated 

populations, competition for nest sites can be so intense that forming a stable breeding  pair is often delayed for up to 6 years. Whenever a mate is missing at a nest or even  arrives a little late, unmated Ospreys known as “floaters” or “intruders” will fight at the  nest for breeding privileges. Even battles to unseat a pre-existing breeding pair are  common. (Last year, the battles were so intense at the Salt Point nest that the original  owners failed to breed.)  

Most Osprey females rush to migrate south in late summer, but males tend wait until at  least September. On the east coast, migration distances vary with the season. Spring  migrants travel shorter distances compared to fall travelers due to their more directed  flight paths. Many spring migrants take a direct route crossing the Caribbean and  heading up the  

Ophelia carrying algae at Salt Point, courtesy of Cindy and Karel Sedlacek. 

east coast. Since early arrival on the breeding grounds is advantageous, natural selection should favor Ospreys that expend the extra energy needed to compensate for  wind drift, enabling them to take the shortest route to their breeding areas. In the fall, 

there is no biological imperative to rush. Therefore, natural selection favors Ospreys  that employ a fall migration strategy to minimize energy expenditure.  

Fall migration by east coast migrants is also slightly longer because the southbound  birds continue over land from Cuba to Hispaniola, and from there proceed across the  Caribbean. This is a longer overall route than flying directly from eastern Cuba to South  America, but minimizes the distance covered over the open water of the Caribbean Sea.  

Osprey reclaimed it’s nest, courtesy of SC Whalen. 

This is important because the fall migration coincides with the hurricane season in the  Caribbean, and Ospreys are vulnerable to bad weather over open water. In contrast,  Ospreys on spring migration do not have to contend with this challenge and therefore 

can use a more direct over-water migration route. On the spring trip, birds leaving South  America are funneled to the peninsulas on either side of the Gulf of Venezuela. As they  subsequently head north, the prevailing trade winds push them west. This creates a  longer overwater crossing than but a shorter overall trip across the Caribbean region.  

Keep your eyes to the sky, they will be returning in a week or two! 

Eyes to the sky! 

Candace 

Candace E. Cornell  

Friends of Salt Point  

Lansing, NY 

cec22@cornell.edu