Blog # 296 Do Tailwinds Favor Osprey Migrations?


Migrating female Osprey in front of cumulus clouds, courtesy of Tim Milner. 

How do winds affect the return of Cayuga Lake’s Ospreys? Studies demonstrate that  most migrations coincide with favorable tailwinds as wind affects both the speed and the  energy cost of the birds. However, soaring migrants like Osprey are less dependent on  tailwinds and will migrate without them. 

Ospreys and other large raptors are not built for sustained wing-flapping and easily  become exhausted. Instead, they are proportioned to optimize thermal soaring–gliding  flight. Their long, narrow wing-shape give them a high aspect ratio affording more lift  and enabling sustained endurance flight. In contrast, low aspect ratio wings are best for  swift maneuverability. 

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A comparison of wing shapes and purpose, adapted from eku.edu. 

Over land, ascending air currents are generated either by uplifting off mountains or by  thermals. Ospreys hitch rides on these thermals, soaring upward and then gliding horizontally to the next thermal. By doing so, the Osprey expends very little energy  travelling long distances. 

Flightpath of a hawk riding a thermal, adapted from Aviation Weather.ws. 

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Most large raptors avoid crossing seas during migration because of the lack of updrafts  and scarcity of thermals (atmospheric convections) over temperate waters. The Osprey  is the exception. As on land, thermals do form over open waters if the surface waters  are warmer than the overlaying air, but they are not as strong. Since Ospreys can fly  over several hundred miles of open water in one stretch, they will tackle large bodies of  water like the Caribbean and the Mediterranean on migration. Recent stiudies1,2 show  that Ospreys are able to locate these rarer and weaker marine thermals and utilize  them. However, it is more work for the Osprey to ride a thermal over water than it is  over land. Marine thermals (convection cells) are weaker, making it harder for the birds’ to climb within the thermal and necessitating that the birds keep flapping the entire time.  Still, this gliding flight gives the Osprey the advantage it needs to cross oceans that few  dare. 

Osprey on nest on Rt. 20 near Montezuma National Wildlife Refuge today, CE Cornell. 

Most of the Osprey returning home island-hop their way across the Caribbean with  limited stretches over the sea. However, younger birds tend to take unique paths  homeward. The 2021 Osprey migration is on. Ospreys are travelling north, arriving  along the New Jersey shore. None have been spotted at Braddock Bay, Hamburg Hill,  or Derby Hill to date. We’re having spring-like calm sunny weather—perfect weather to  welcome our Ospreys home. Two have already been seen flying up Cayuga Lake  today, and more are on the way . . . at least 150 pairs. Get out there and enjoy the  soming migrations.

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Eyes to the sky!  

Candace  

Candace E. Cornell  

Friends of Salt Point  

Lansing, NY  

cec222@gmail.com 

EYES ON OSPREYS 

WATCH! 

Coming Soon! Salt Point Osprey Nest Cam 2021 

READ! 

On Osprey Time Ospreys of Salt Point 

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Cayuga Lake Osprey Trail 

1Duriez, Olivier; PERON, Guillaume; Gremillet, David; Sforzi, Andrea; Monti, Flavio  (2018): "Migrating ospreys use thermal uplift over the open sea." The Royal Society.  Collection.  

2Duriez, Olivier; PERON, Guillaume; Gremillet, David; Sforzi, Andrea; Monti, Flavio  (2018): Supplementary material from "Migrating ospreys use thermal uplift over the  open sea." The Royal Society. Collection. 

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