So today I took a trip to Poplar Island which is in the Chesapeake Bay in Maryland. We took a bus tour and saw many amazing birds including many lifers. I heard before that certain types of birds that I thought spent the fall and winter in the state are known to say year round (i.e. scoters and mergansers) and some time during my trip I encountered all three scoter species and a red-breasted merganser and heard people saying that there could be long-tailed ducks.
This had me wondering why those birds who I thought migrate to the area for the colder months stayed throughout the summer. Som of the scoters I saw appeared to be molting. There were no ducklings? The same goes for this eclipse plumage merganser and a couple of adult ring-billed gulls there too.
So what caused these birds to not migrate and apparently not breed where they’re staying at?
This behavior is not common among migratory waterfowls, but is not unlikely also.
Some migratory birds do not return to their breeding places (e.g few lesser whistling ducks, gadwalls etc. in India) if food source is available, climate/habitat is considered as suitable. They become resident birds there. Few can adapt for breeding also in their winter shelter subject to availability of factors required for it.
However, these are not exhaustive factors which may vary from species to species and from place to place.
PS: The post, however, covers some common situations.
Although common and red-breasted mergansers visit India during the winter months, I have never seen any of them stay here all year round. I have not seen any kind of Scoters in India.
See this post regarding gulls and loons. The answer will be the same for scoters, long-tailed ducks, and red-breasted mergansers. Immature sea ducks regularly summer in bays and estuaries along the coast, well outside their breeding range.
As I hinted in this post, the way range maps are formatted is much more suited to migratory songbirds and doesn’t really capture the more nuanced ranges of waterbirds. In many distribution descriptions for these species (e.g., Birds of the World), you’ll see the categories Breeding Range, Nonbreeding Range, and Summer Nonbreeding Range, the latter is seldom expressed on range maps.
Here in Northeast Ohio, we have a male lesser scaup that’s been around for a few years now. It mainly stays in a stretch of the twisty Cuyahoga River about a mile and a half (as the duck flies) from the mouth of the river where it meets Lake Erie. We call him Lester. We think we see him with a female when the other scaups migrate through. But, he always ends up back in his area in the river after the other ducks are gone. Lester appears to be healthy. No problems flying or paddling. Maybe he was hurt or sick or couldn’t get enough food to continue migration a few years ago and decided to stay. It’s a mystery. But, he’s there all year.
When I lived in Minnesota, one year there was a Greater White-fronted Goose that decided to spend the summer in a nearby marshy area. I remember it clearly because every single time I went to one of my favorite spots, I had to report that “rare” goose. I remember at one point I started commenting on how, for example, that goose had lived in the county long enough to register to vote in local elections.
The consensus at the time was that the bird just wasn’t going to breed that year and could not be bothered to fly any further north when it had it pretty good right where it was. We had them passing through by the hundreds and thousands every year, but only that one stayed. (Well, later in the summer I found out there were 2 or 3 living back there somewhere. It was a pretty good-sized marshy area, but the part we could actually see into was a glorified mud puddle.)
