Date: 3/18/26 8:18 am From: 'PAUL ROBERTS' via Arlington Birds <arlingtonbirds...> Subject: [Arlington Birds] Bald Eagles in Eastern Massachusetts
This week, and perhaps for a few more days, if you've been keeping your eyes open near local bodies of water that are experiencing "ice out," as several posters have indicated, you have your best opportunities to see Bald Eagles. Back in the late 20th century, your best chance to see the rare Bald Eagle was in March "ice out," when small numbers of adult birds were migrating back north for the breeding season, moving with the isotherms during "ice out." When ice melts, it opens bodies of water to ducks and precipitates more fish activity. Secondly, anything that died during the ice up, or during the winter (starvation?) should be released from the ice, attracting gulls and eagles moving back north at this time. Just follow the thaw to find free food. Julie and I would go to Great Meadows in Concord during ice out. Because of the ravages of DDT, we no longer had locally breeding birds, and most adult eagles were not successful breeding, so you saw largely adults, as the population crashed. People literally forgot how different juvenile and immature eagles looked, especially when they saw eagles with "Osprey-like eye-stripes." Through the combined efforts of thousands of individuals and the federal, Canadian and state governments, eagles began to come back as a breeding bird. During 2024, there were at least 88 territorial pairs in Massachusetts and perhaps thrice that number in Maine. However, it took eagles a while to come back, as they do not generally breed until they are 4 years old or older, and they frequently do not succeed in their first year or two of breeding. Then they average about 2 eggs per pair. Juvenile mortality is around 50% (The mortality rate decreases as you get older.) It takes 2 pairs roughly 6 years each before they produce a breeding pair. So the eagles will not have "grandchildren" for roughly 10-12 years. The population increased slowly. Historically, we saw few immatures in Massachusetts, and most of those were birds believed to be from Northern New England and maritime Canada who moved south as ponds, lakes, and rivers iced up, peaking in late December or early January. We had annual wintering censuses of Bald Eagles throughout the continent in early February. With expanding populations, we are seeing many more immatures in our area than we did 20 or 30 years ago. With global warming, data suggest that a smaller percentage of "our northern Bald eagles" migrate south for the winter. Maine juveniles or immatures tend to remain in Maine, but largely move toward open waters near the coast. Massachusetts eagles apparently are behaving similarly, moving largely towards large or moving bodies of water that provide access to fish and waterfowl during most of the winter, and moving towards the coast as freeze-ups get harsher. Territorial adults in Massachusetts and Maine apparently tend to not migrate south during the winter because they hate to give up "rights" to their territories. They remain on or close to territory for as much of the year as they can. Juveniles ( identifiable up to a year old) and immatures (birds one year old until they reach full adult plumage, which takes 3 to 5.5 yrs) are not territorial, so they wander around looking for other young birds to socialize with and who hopefully know where to find food. And it's fun (and very educational) to play with other youngsters. Tail chasing (cops and robbers) is fun, and develops skills they can apply as adults. Courtship and nest building behaviors can be seen. Kids watch other eagles looking for food, watch gulls looking for food, and watch fish looking for food, so kids learn how to hunt if they want to survive. Adult Bald Eagles not on territory can be very sociable during winter. During breeding season they want to have a gated community with no other eagles (esp. other adults) around as threats. Juveniles and immature remain pretty social year round, but the larger groups of winter disperse. As ice out progresses, young birds can move farther inland and farther up north, so the population spreads out over much a wider geographic area. Right now (or at least yesterday) is the best chance you have to see eagles in Arlington, Woburn, Cambridge, or most anywhere in our region. They're especially attracted to areas that are just thawing out, as lots of dead (but fresh frozen) fish and ducks become available. Eagles of all ages love cold, windy, sunny days in March. The hormones are surging and the winds provide free lift and opportunities to develop their flying skills. They can roam wider, faster, looking for food. This ice-out concentration is ephemeral but annual, varying considerably from year to year. Keep your eyes open... Best, Paul Paul M. Roberts Medford, MA <phawk254...>
