Wednesday, May 29, 2024

Scientists Find New Osprey Threat

Chesapeake Bay Mag, VA Osprey Researchers Find Unexpected Nest Robber While Investigating Population Decline, minks

Mink are members of the weasel family. American minks don’t grow over 2.5 pounds or about 2 feet in length in the wild. Their luxurious brown fur was popular for coats in years past. They are cute, but they are vicious predators. They can swim well. They will venture far from the water to hunt, and they can even climb trees. They will readily attack and defeat larger prey. As carnivores, they eat eggs, fish, frogs, muskrats, rabbits, and apparently—baby ospreys.

Reese Lukei, Jr is a raptor expert with decades of experience working with The College of William and Mary’s Center for Conservation Biology. He says that after the old days of DDT, osprey enjoyed a successful comeback in the Lynnhaven River and were thriving as recently as five years ago. Unfortunately, that’s begun to change.

“DDT once diminished osprey populations everywhere,” Lukei said. “After DDT was banned, the first osprey returned to a nesting platform in the Lynnhaven in 1979. The number of successful nests grew. There was a peak of Lynnhaven nesting in 2019 with 102 nests counted. About half of those nests were on man made platforms. Nesting began to decline after that, and observers began to notice the disappearance of eggs and chicks from nests.”

Lukei and Keriann Pfleger from the Virginia Aquarium and Marine Science Center (VIMS) began to investigate. “We had eyewitness accounts of owls and eagles raiding osprey nests,” he said. “Crows can form a mob to attack a nest with devastating results.”

Part of their research involved installing cameras on osprey platforms. “Recently, we had a battery issue with a camera,” said Lukei. “When we approached the nest to check on the camera, the nest was empty. We saw no adults. One adult is usually nearby to guard a nest.”

They replaced the battery and checked the memory card. That is when they discovered that a mink had raided the nest. The mink had simply climbed from the water up the pole into the nest.

Lukei called the discovery astonishing. The researchers had no idea minks were raiding osprey nests. While it is too late to make adaptations for this season, Lukei said they will be making plans to address this next year. He noted that it has always been recommended that osprey platforms on land or in marshes be protected with stove pipe against predators. Predator’s claws cannot grasp the metal stove pipe like they can a wood pole. Lukei said they will be applying that advice for platforms in the water as well.

If you’ve never spotted a mink in the Chesapeake Bay region, you may be surprised to learn that the common mink is, well, common, near the water in central and eastern Virginia. They prefer forested, brushy areas that provide cover for dens, according to the Virginia Department of Wildlife Resources.

There's been a movement afoot lately to blame the failure of the the Osprey population in the Virginia on Menhaden fishing. However, this adds a new possibility, predation by mink (and potentially other) predators. Does it add up? I don't know, but that's what the study was designed to get at.

One possibility is that the increasing osprey population has encourage a growth of the predators. Certainly, Bald Eagles have thrived in the Bay as Ospreys have resurged, but we tend to ascribe that to the fact that both were hurt by DDT in the past. Prey and predators tend to run in contrary cycles, with high numbers of prey encouraging a subsequent boom in predators, which reduces the prey population, and causes a decline in predators. Could this cycle be occurring in the Bay region between Ospreys and the species that take advantage of them?

The Wombat has Rule 5 Sunday: Something Blue up and garnering clicks at The Other McCain.

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