Eastern Dakotas Ground Crew Update 3, and Some Notes on Duck Sex

Written by Pam Garrettson
Sunday, May 23, 2010

Pam Garrettson.We have had a week of dry, sunny weather, and are heading into the home stretch of the survey. We have four more air-ground segments left to do. Overall, the story for this year in the Eastern Dakotas has been lots of water and lots of ducks. However, we continue to notice the loss of Conservation Reserve Program (CRP) lands, which are very important grassland habitat for upland-nesting ducks. Thus, we were pleased to reach a couple of our Coteau segments, which are hilly, primarily used for grazing, and have an abundance of semi-permanent and permanent wetlands. These also make suitable habitat for diving ducks that build nests of aquatic vegetation over the water.

Compared to puddle ducks, diving ducks have smaller wings relative to their body size, and legs set further back on their bodies. This makes them excellent underwater swimmers, but they must paddle over the water to take flight, and they walk on land only rarely and with difficulty. The diving ducks we typically see in our crew area include several similar species: canvasbacks, scaup, and redheads, and a rather different beast called the ruddy duck (see picture). A member of the genus Oxyura, known as the stifftail ducks, breeding-season males have a comical appearance and a spectacular courtship display known as bubbling. They cock their tails up, inflate their throats with air, and beat their breasts with their bills, making bubbles in the water in front of them. They display to females, males, by themselves, even to our crew, so the display is thought to serve a territorial as well as a courtship function. Ruddy ducks are also known for having a penis half their body length, sometimes preening it as part of their post-copulatory display.

In general, ducks are among the only 3% of birds that have penises, presumably to ensure sperm transfer during copulation in the water. This means that forced copulation (see picture) can also occur. So called forced extra-pair copulations (FEPCs) are thought to be an alternative reproductive strategy for males, and are characterized by the female’s resistance, and her lack of inciting behavior beforehand and her typical post-copulatory display. The male she is paired with tries to guard against FEPC attempts by other males to ensure that he fertilizes her eggs. Although FEPCs make up as many as 30% of copulations in some species, they account for less than 4% of fertilizations, which suggests that females may have evolved their own strategies. Recently, Patricia Brennan and colleagues found that in duck species with greater frequencies of FEPCs, penises were larger and more structurally complex, but so were female reproductive tracts, which may allow females to exclude sperm from forced copulation attempts, an evolutionary arms race of sorts.

A ruddy duck struts his stuff in southeastern North Dakota.  Photo by Dan Collins and Joshua J. White.

A ruddy duck struts his stuff in southeastern North Dakota. Photo by Dan Collins and Joshua J. White, USFWS

Dan Collins scans a large pothole visible from the truck with a spotting scope.

Dan Collins scans a large pothole visible from the truck with a spotting scope. Credit: Joshua J. White, USFWS

Mallard copulation west of Sisseton, South Dakota.  This appeared to be a forced copulation.

Mallard copulation west of Sisseton, South Dakota. This appeared to be a forced copulation. Credit: Joshua J. White, USFWS

A red-necked grebe west of Streeter, North Dakota.  These are uncommon in the crew area;  Western and pied-billed grebes are more typically seen.

A red-necked grebe west of Streeter, North Dakota. These are uncommon in the crew area; Western and pied-billed grebes are more typically seen. Credit: Joshua J. White, USFWS

An American avocet on one of our North Dakota airgrounds.  The mudflats around recessed potholes provide habitat for many breeding and migrating shorebirds.

An American avocet on one of our North Dakota airgrounds. The mudflats around recessed potholes provide habitat for many breeding and migrating shorebirds. Credit: Joshua J. White, USFWS

Dan Collins surveys a wetland on the Missouri Coteau in North Dakota.  This area is characterized by more permanent wetlands and grasslands primarily used for grazing.

Dan Collins surveys a wetland on the Missouri Coteau in North Dakota. This area is characterized by more permanent wetlands and grasslands primarily used for grazing. Credit: Joshua J. White, USFWS