David W. Foster is one of the top birders in Duval County, Florida. He is also a regional reviewer for ebird.org, and follows-up on data submitted to the web site.
I recently submitted a list that reported 33 Mottled Ducks at Spoonbill Pond (Big Talbot Island State Park, Duval County, FL). David was kind enough to explain why this number was unlikely. With his permission, I am reprinting his response so that birders in Northeast Florida can better determine when they are sighting a true Mottled Duck.
Mottled Duck populations have been in decline for the past several years – about an estimated 78% decline since 1966 per some sources such as Breeding Bird Surveys. Habitat loss is one issue but interbreeding with feral Mallards is a huge issue.
Migrating Mallards only winter in Northeast Florida; they leave for the breeding season. [But] the introduction of non-migratory feral Mallards [led to] extensive hybridization between feral Mallards and native Mottled Ducks. True Mottled Ducks are in trouble…
[Additionally], South Carolina wanted Mottled Ducks, so they brought in [a subspecies native to the West Gulf Coast], which is a distinct population from the Florida subspecies. So now… the West Gulf Coast Mottled [is] interbreeding with our Florida Mottled Ducks. That complicates identification at a level beyond just Mallard X Mottled. (**A recent paper about identifying Mottled Ducks and hybrids suggested the default choice in NE FL should be Mallard/Mottled.)
Birders, especially at Spoonbill Pond, have been reporting Mottleds as a default. They look superficially like Mottled Ducks so that is how they are counted. When I gave a critical eye during my recent visits, most were hybrids and the others were inconclusive. Many of the Spoonbill Pond observations are made at 100 yards or more making it even more difficult to clearly identify the field marks.
To use Mottled Duck, it must be considered a “pure” Mottled, not mostly or 90% Mottled. The observer should look carefully at each duck using three or more field marks and eliminating traits of hybridization.
The more obvious traits of hybridization include one or more of the following:
- white in the tail (or anywhere else)
- solid black on the rear end (upper and or lower)
- a long eyeline that extends to the back of the head
- heavily streaked cheeks
- a little or [absent] gape spot (the black spot at the base of the bill)
- a Mallard “tail curl”
- any green on the head
- reddish brown on the breast.
As for juveniles, considering the prevalence of hybridization it is difficult to call them true Mottleds even if the parent is a true Mottled Duck.
Many birders just see Mallards or Mottleds and nothing in between. Unfortunately, we birders are doing a huge disservice to Mottled Ducks by making it look like there are many more than actually exist.