Ducks in jester’s garb

By Bill Chaisson
Of a Feather
The stretch of coastline between Cape Ann in Massachusetts and Cape Neddick in Maine is arguably the last stretch of barrier island shore on the East Coast. It is the dominant physiographic form of the Atlantic boundary with the United States. The islands are generally broken at intervals by inlets, often where rivers and creeks enter the ocean. The Hampton River enters the Gulf of Maine between Locke Point in Hampton Beach on the north and Beckmann’s Point in Seabrook Beach to the south. There is a wide lagoon behind the two barrier islands where the Hampton River and several tidal creeks come together. It was there, near the marina, that on Jan. 2 someone reported to NH Bird Forum that they saw a single harlequin duck (Histrionicus histrionicus).

The photographs posted to eBird showed the bird to be a juvenile or first-winter male, the plumage of which does not recall at all the garb of a medieval jester. It is a black duck with a large white smudge of indeterminate shape between the bill and eye and a circular white patch behind the eye. It is possible the bird is an adult female; the white patch behind the bill is generally bolder in the immature males, but published photos (I have never seen one) suggest there is overlap.

The male ducks in breeding plumage are difficult to describe. Overall they are dark slate gray with bright rufous flanks and rufous crescents on either side of the crown. The white patches on the head are bold and well defined, and there is a white vertical bar on the neck and two more white bars on the chest. There are more patches of white on the secondaries and wing coverts. It also has a long pointed tail, although not as long as that of the long-tailed duck or a pintail.

The sighting of the harlequin duck at Hampton is unusual in that they are normally found off rocky coasts, foraging over submerged rocks, from which they will pluck mussels, one of their favorite foods. They will, however, eat other small invertebrates, such as small crabs and snails, which they sift out of the mud with their bills.

The sighting is also worth reporting because this species is not particularly common anywhere in the East compared to in the western United States and Canada. In his 1925 Life Histories of North American Wild Fowl, Arthur Cleveland Bent considered them quite rare south of Maine. Through the 20th century its numbers declined in its eastern range and in 1990 the Canadian government declared it to be endangered. G.J. Robertson and R.I. Goudie, writing at birdsoftheworld.org, state that the eastern numbers were likely never more than 10,000 birds and that only about 1,500 winter off the U.S. coast.

While the western population is more abundant, its numbers are threatened by hunting, habitat destruction, and pollution. Because it is tame and forages relatively near to shore, it is more easily taken by hunters. The flesh of the Aleutian population was found to have high levels of benzo(a)pyrene, which leaches out of creosote used to coat piers and is a component of diesel soot. A single event, the March 1989 wreck of the Exxon Valdez in Prince William Sound, Alaska significantly affected the species’ numbers, again because of its preference for shallow, in-shore habitat.

It was more abundant and widespread in the geologic past, with fossils found in Italy and North Carolina. It was also more widespread in the historical past. Populations in Colorado, Idaho, and Montana have disappeared relatively recently. It once bred as far south as northern California, but this population too may no longer exist.

However, while Bent considered them rare south of Maine, they are now spotted as far south as Chesapeake Bay because jetties, breakwaters, and abutments have created the rocky habitat they prefer in regions that are naturally dominated by sand and mud substrates. They are also reported to be increasing their numbers in the Great Lakes.

Writing in the 1920s Bent embraced the idea that the western populations were a separate subspecies, but by the 1970s it was decided that there was insufficient evidence for a distinction and no subspecies are recognized today.

In 1996 Bradley C. Livezey of the Carnegie Museum of Science in Pittsburgh published in the journal Condor a comprehensive phylogenetic analysis of all the sea ducks (tribe Mergini). For 25 species he scored 137 different morphological characters with respect to their primitive or derived state and used statistical analysis to build branching “family trees” that reconstruct hypothesized evolutionary relationships among the taxa.

Livesey’s most “parsimonious” (requiring the least number of steps) arrangement shows the harlequin duck to be most closely allied with the scoters, but not very closely. In fact, H. histrionicus is alone on a branch in the tree because it has so many derived (specialized) characters or autapomorphies, which causes it to be distinct from other sea ducks. The harlequin duck has 11 autapomorphies, 7 of which are unique within the entire tribe.

More recent molecular genetics work by Philip Lavretsky at the University of Texas, El Paso and others (in the journal Molecular Phylogenetics and Evolution, 2021) confirmed the morphological phylogenetic tree constructed by Livezey. However, Lavretsky et al. also found that some of the diversity in this tribe is due to gene flow created by repeated hybridization among species. Three H. histrionicus specimens were found to have common eider DNA and 2 harlequin ducks even included DNA from outside the tribe (common merganser and bufflehead).

Lavretsky et al. noted that all the harlequin ducks with hybrid ancestry were from the east coast population. They hypothesized that these extra-species matings took place during a drastic decline in the population during the 1980s. Furthermore, while most duck populations are heavily biased toward males, eider and harlequin gender ratios are nearly 1:1 in the east. Lavretsky et al. believe the relative rarity of males abetted hybridization.

— Bill Chaisson has been a birdwatcher for over 50 years.