Coley is very much a homebody these days, staying in an even tighter “Center of Activity” than usual with his typical occasional flights out to fish. He is not visibly nervous about migrating, a condition known as Migratory Restlessness that most birds display just before migrating, but he has got to be feeling something as his body prepares for migration. In about two weeks, he will take off to begin his 2,700-mile journey back to Jamaica Bay. So for now it is eat and rest, eat and rest, eat and rest!
Below I will address four more questions about Ospreys and Coley, but first I have a few questions for you.
- When do you think that Coley will leave Bird Marsh in Colombia for his flight to Jamaica Bay?
- What day do you estimate that he will arrive on his nest in Jamaica Bay?
- Who do you think will arrive home in Jamaica Bay first, Coley or his mate?
Leave your answers in the comments! Here are a few more answers to your questions about Ospreys and Coley:
How does Coley know when to start his migration?
This is a question that is hard to answer. Many birds respond to changing day length that at some point triggers a migratory preparation such as adding body fat to fuel the long trip. When environmental conditions such as wind direction and speed, atmospheric pressure, temperature or some unknown input or combination click in Coley’s brain that will turn him from a lethargic winter resident into a migrating machine. Quite literally, he will be perched resting one moment and the next he will be off like a shot out of a canon. The perplexing thing about the day length’s influence on birds that winter in the tropics is that the length of daylight does not change much throughout the year. So there are likely many factors that the birds can detect that prepare them for migration and then send them off at almost the same time each year.
Will Coley follow the same route north to Jamaica Bay that he followed south to Bird Marsh in Colombia?
The return migration almost will be the mirror image of the fall migration. A bird that we have tracked on Nantucket, Señor Bones, migrated south in the fall and north in the spring in 2011 and in 2012 in almost exactly the same path. Minor variations occurred when he was flying over the Caribbean and over the Straits of Florida between Cuba and Florida; these variations were caused by drift with the prevailing winds at the time of the different flights. It took Coley just 17 days to fly 2,700 miles from Jamaica Bay to Bird Marsh in Colombia in the fall. Let’s see how long it will take him to do the return trip.
How does Coley know where to go, that is, how does he navigate to find his way back to his nest in Jamaica Bay?
Clearly Ospreys use many methods to navigate the route from their winter retreat to summer home, and return of course. Since Ospreys do not migrate as a group, but as individuals, they cannot learn from each other. Some studies have shown that birds migrate using celestial cues, such as star patterns, or the position of the sun through the day and at the time of year. Others have shown that the earth’s magnetic forces add them in migration. Some learning goes on through trial and error, and once successful, it almost appears as if they have their own GPS navigational system to guide them along the way. The long and short of it is that we do not know for sure how they do it, but we do know that whatever they use, they can travel with remarkable accuracy from place to place.
Will Coley eat on his way home or will he rely on his fat stores to fuel his migration?
Coley will fish along the way to keep up his strength. It appears that most fishing takes place early in the morning before they start the day’s flight, or during rest stops lasting a day or so along the way. This will vary depending upon the distance traveled, the success of earlier fishing attempts, etc. Clearly Coley and other Ospreys do not appear to fish when they travel out across large bodies of water such as the Straits of Florida or the Caribbean Sea.
Do you have any questions about Coley or about Ospreys? If so, please leave a comment and I will try to answer them for you in the next post.
I’ll get the next report out in about one week, when Coley should be close to heading north. Once he starts north, I will prepare updates about every three days.
Thanks again for your input and support.
Coley and Dr. Bob signing off.