Blog # 369 Spring Migration Across North America

Migrating Osprey, courtesy of Save Coastal Wildlife. 

Spring is approaching, bringing with it the welcomed return of North America’s Ospreys. But this is  not just an east coast phenomenon; it happens across the US and Canada. Since the DDT era,  Osprey populations have recovered and increased their range across the US and Canada. By now,  North American Ospreys have left their wintering grounds in Central and South America and are  high-tailing it northward before their nesting sites are usurped.  

A study in 2014 by Martell et al. looked at the migration strategy—the set of rules governing  migration—of spring migrants in three sections of the US and elucidated similarities and  differences among these populations. GPS-tracked Ospreys used regional flyways across the  eastern, midwestern, and northwestern US and southwestern Canada (‘‘western’’), revealing flight  patterns.  

Regional Spring Migration Routes 

How do Osprey spring migration routes differ, region by region, across the US? 

East Coast Ospreys. The majority of the east coast Ospreys winter along South American  coastlines and along its interior tropical rivers. In spring, migrants are funneled into two  peninsulas bracketing the Gulf of Venezuela (Guajira in Colombia and the Paraguana´ in Venezuela). From there, the birds fly up to 750 miles nonstop over the Caribbean to Haiti,  Jamaica, or Cuba, a crossing taking 27–40 hours. The birds continue northwest until they make  landfall in the Florida Keys and then head up through Florida and onward to their breeding grounds.

R to L, East coast, Northwestern, and Midwest Osprey spring migration routes (Martell 2014). 

Northwestern Ospreys. After traveling north from their Central and South American wintering homes,  they followed the Central American land route north to Mexico and the US. Most birds followed the  valleys westof the Rocky Mountains to points north and west. 

Midwest Ospreys. Midwestern Ospreys returning to their nests take a hybrid route north. Part of the  population island-hops across the Caribbean the way the east coast birds do, before heading  north/northwest through Florida and on to points in the Midwest. 

Departure dates from wintering grounds and arrival dates on breeding grounds do not differ  significantly between adult male and female Ospreys. There is, however, a difference in both  departure and arrival dates based on region, with east coast Ospreys leaving their wintering grounds and arriving on their breeding areas before their counterparts in the Midwest and  western North America. Since Ospreys in the east are primarily coastal, they live near water that  rarely freezes. This allows them to return earlier than those in the Midwest, which have to wait for frozen inland lakes and rivers to thaw. 

 EAST COAST MIDWEST WESTERN  

MEASUREMENT MALES FEMALES MALES FEMALES MALES FEMALES 

Earliest Departure 25 February 9 February 16 March 10 March 13 February 10 March Earliest Arrival 11 March 22 March 2 April 7 April 4 April 28 March Latest Departure 7 April 6 April 1 April 22 March 19 April 11 April Latest Arrival 15 May 23 April 23 April 27 April 13 May 23 April Mean Departure 16 March 9 March 24 March 16 March 14 March 30 March Mean Arrival 4 April 6 April 14 April 17 April 15 April 13 April Median Departure 18 March 8 March 24 March 15 March 10 March 1 April Median Arrival 5 April 6 April 15 April 19 April 6 April 16 April

Compared to fall migrations, males from all three regions and all east coast Ospreys spend less  time migrating and stopping over to eat in the spring. On average, the birds travel shorter distances while traveling farther each day during these spring flights. 

There is no trend for sex-specific arrival behavior as the selective pressure is equal on both sexes to  arrive on the breeding grounds as soon as possible. Both male and female Ospreys show great fidelity to their nesting sites and to their mates and arrive at the nest at about the same time. It’s  been shown that the sooner pairs begin breeding, the greater the success of their fledglings as  

they have more time to learn fishing before their initial migration. In saturated populations,  competition for nest sites can be so intense that breeding does not begin until 5-6 years old. Late  arrival for either sex can lead to intense battles—sometimes a battle to the death—to reclaim the  nest from early-arriving, same-sex individuals.  

Eyes to the sky! 

Candace 

Candace E. Cornell 

Friends ofSaltPoint 

Lansing, NY 

Cayuga Lake Osprey Network 

NY cec222@gmail.com 

  

EYESTOTHESKY! 

WATCH! 

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READ! 

OnOspreyTime: Ospreys of Salt Point 

VISIT! 

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