Fish eggs survive being eaten by ducks


This 2009 video is called Mallard Duck – HD Mini-Documentary.

By Carolyn Wilke today:

Fish eggs can hatch after being eaten and pooped out by ducks

In the lab, only a few carp eggs survived the dangerous trip through birds’ innards

For fish eggs, getting gobbled by a duck kicks off a harrowing journey that includes a pummeling in the gizzard and an attack by stomach acids. But a few eggs can exit unscathed in a duck’s excrement, possibly helping to spread those fish, including invasive species, to different places, a new study finds.

It’s been an “open question for centuries how these isolated water bodies can be populated by fish,” says fish biologist Patricia Burkhardt-Holm of the University of Basel in Switzerland, who was not involved with the work. This study shows one way that water birds may disperse fish, she says.

Birds’ feathers, feet and feces can spread hardy plant seeds and invertebrates (SN: 1/14/16). But since many fish eggs are soft, researchers didn’t expect that they could survive a bird’s gut, says Orsolya Vincze, an evolutionary biologist at the Centre for Ecological Research in Debrecen, Hungary.

In the lab, Vincze and her colleagues fed thousands of eggs from two invasive carp species to eight mallard ducks. About 0.2 percent of ingested eggs, 18 of 8,000, were intact after defecation, the team found. Some of those eggs contained wriggling embryos and a few eggs hatched, the team reports June 22 in the Proceedings of the National Academy of Sciences. It’s not clear yet whether eggs survive in this way in the wild.

Most of the viable eggs were pooped out within an hour of being eaten, while one took at least four hours to pass. Migratory ducks could travel dozens or possibly hundreds of kilometers before excreting those eggs, the scientists suggest.

Though the surviving egg count is low, their numbers may add up, making bird poop a possibly important vehicle for spreading fish. A single carp can release hundreds of thousands of eggs at a time, Vincze says. And there are huge numbers of mallards and other water birds throughout the world that may gorge themselves on those eggs.

Mallards usually eat plants. They have trouble eating meat, even an ‘easy’ small dead fish, as I have seen.

North American pintail ducks in trouble


This 2011 video from the USA says about itself:

Northern Pintail courtship displays in Sacramento Valley, California. Courtship involves drakes “showing-off” their remarkable plumage both on the water and in aerial courtship chases.

From Penn State University in the USA:

Changes in cropping methods, climate decoy pintail ducks into an ecological trap

Important waterfowl species struggling with conditions in the Prairie Pothole Region

May 28, 2020

After a severe drought gripped the Prairie Pothole Region of the U.S. and Canada in the 1980s, populations of almost all dabbling duck species that breed there have recovered. But not northern pintails. Now, a new study by a team of researchers suggests why — they have been caught in an ecological trap.

The Prairie Pothole region straddles the U.S.-Canada border and sprawls from central Iowa in the south to Alberta in the north, covering a large swath of Minnesota, South Dakota, North Dakota, Manitoba and Saskatchewan in between.

“With increasing cropland cover in the region, pintails have been selecting for cropland over scarce alternative nesting habitat, probably because it is similar to the native mixed-grass prairie they evolved to nest in,” said lead researcher Frances Buderman, Penn State. “That behavior results in fewer pintails the following year due to nest failures from predation and agricultural practices.”

The U.S. Fish and Wildlife Service’s North American Waterfowl Management Plan calls for more than 4 million pintails, but recent estimates are only half of that. The reason pintails are not thriving like other dabbling ducks, according to Buderman, assistant professor of quantitative wildlife ecology in the College of Agricultural Sciences, is that they are being “misled” by modern cropping methods and climate change into choosing risky nesting habitat.

Also called puddle ducks, dabbling ducks frequent shallow waters such as flooded fields and marshes. They feed by tipping up rather than diving. There are 38 species of dabbling ducks — they float high in the water and are swift fliers.

By their very nature, pintails may be vulnerable to the ecological trap, Buderman explained. Despite being an early-spring nester — a quality that typically would allow for reproductive “plasticity” to climatic conditions — pintails have demonstrated inflexible breeding behavior, such as being unwilling or unable to delay nest initiation and being less likely to renest than most other waterfowl.

“Inflexible breeding behavior may result in greater vulnerability to unpredictable weather events and changes in climactic conditions,” she said. And given their preference for nesting among landscapes of grass-like, low-lying cover, pintails readily nest in fields of stubble in untilled agricultural fields. “Unlike other ducks that generally avoid nesting in stubble, pintails in the Prairie Pothole Region commonly select crop stubble nest sites and often select it over remnant patches of grass and other cover.”

Pintails often initiate nests before remaining stubble fields are worked by farmers in the spring, making nests vulnerable to mechanical spring tilling and planting of remaining standing stubble, Buderman explained. That can destroy a large percentage of initial nests. Exacerbating the effect of pintail selections over time, the amount of land in the Prairie Pothole Region annually tilled for spring-seeded crops has increased by approximately 34% since 1959.

Dabbling duck incoming

Another factor that is contributing to pintails’ decline, researchers contend, is a trend in some areas of the Prairie Pothole Region to manipulate drainage to consolidate surface water into larger and deeper wetlands that dry out less frequently and have more surface-water connections to other wetlands.

Those drainage practices make mowing around ponds easier for farmers, and most waterfowl species have coped thus far, but it hasn’t been good for pintails. Wildlife scientists suspect the birds need the smaller, shallower, ephemeral ponds with which they evolved. For reasons not clearly understood, pintails appear to be particularly sensitive to changes in the number of productive, small wetlands that have occurred across the Prairie Pothole Region.

Buderman pointed out that funding partner Delta Waterfowl is working hard to restore these valuable seasonal wetlands on the U.S. side of the region by establishing a Working Wetlands program in the U.S. Department of Agriculture via the federal farm bill.

To reach their conclusions, researchers used more than 60 years of data from the U.S. Fish and Wildlife Service and the Canadian Wildlife Service, which have monitored spring population sizes for North American waterfowl since 1955. They published their results in the Journal of Animal Ecology.

That information is organized into regions that reflect both habitat differences and political boundaries. For many decades, waterfowl have been counted on both sides of the border by aerial crews flying fixed-wing aircraft along established transect lines at low altitude, while simultaneously, ground counts are conducted at ponds on a subset of air-surveyed areas.

To analyze population dynamics, researchers developed a complex model to deal with a huge dataset that took days to run on a powerful computer, which calculated a “breeding pintail count” for the survey period. The model — which also took into account precipitation, climatic conditions during the breeding season and pond dynamics — allowed researchers to identify the relative influence of long-term changes in climate and land use on both the selection and quality of habitat for pintails in the Prairie Pothole Region.

Common whitethroat, mallards and gadwalls


Mallards and gadwall, 20 May 2020

After my earlier blog post, still 20 May 2020 in the sand dunes nature reserve. We walked away from the lake, just south of Egmond aan Zee village. Just to the south of that lake, in the next lake, were these three mallards dabbling, and a gadwall duck swimming behind them.

Further away, a little grebe swimming.

Common whitethroat, 20 May 2020

On a bush above the lake, this common whitethroat singing.

Common whitethroat, on 20 May 2020

An oystercatcher flying.

Mallards, 20 May 2020

Meanwhile, the mallards were still dabbling.

Gadwall, 20 May 2020

The gadwalls had moved to another part of the lake.

Gadwall, on 20 May 2020

As we walked back, a brimstone butterfly.

Red-crested pochard couple and other birds


Red-crested pochards, 2020

This photo shows a red-crested pochard couple. The female on the left, the male on the right.

Red-crested pochards, in 2020

They swam on 2 April 2020 at De Wijde Blik lake in the Netherlands.

Red-crested pochards and waves, in 2020

As they swam, there were big waves in the water because of the wind.

Reed, 2 April 2020

Even among reed plants along the bank.

Het Hol, 2 April 2020

At Het Hol nature reserve, the water was a bit quieter.

Grey heron, 2 April 2020

A grey heron.

Lambertszkade, 2020

These two photos show the footpath to the Lambertszkade hide.

Lambertszkade, in 2020

Like last time at the Lambertszkade hide, on 2 April a chiffchaff sang. Tufted ducks. A mute swan couple. Mallards. Coots. Moorhens.