Whooping cranes form larger flocks as wetlands are lost -- and it may put them at risk

Date: April 2, 2020

Source: Cell Press

Over the past few decades, the critically endangered whooping crane (Grus Americana) has experienced considerable recovery. However, in a report appearing April 2 in the journal Heliyon, researchers found that habitat loss and within-species attraction have led whooping cranes to gather in unusually large groups during migration. While larger groups are a positive sign of species recovery, the authors say that these large groups mean that a disease outbreak or extreme weather event could inadvertently impact a substantial portion of this still fragile population.

"Whooping crane conservation is one of North America's great success stories," says Andrew Caven, Director of Conservation Research at Crane Trust, a non-profit organization dedicated to the protection of critical habitat for whooping cranes and other migratory birds. During the 1940s the whooping crane population fell to 16 birds, largely due to overhunting. However, after concerted conservation efforts, their numbers have increased 30-fold. "We had this species at the brink of extinction, and now there are over 500 birds. As conservation biologists, we've been extremely inspired by that."

Even with this boom in whooping crane numbers, researchers are observing larger migratory flocks than they would expect from population growth alone. Historically, groups of migrating whooping cranes seldom exceeded a family unit. "Twenty years ago, a group of nine was notable; something you'd write in your natural history notes about. But now it's becoming something quite regular. In the recent years we've seen bird groups over seventy multiple times."

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Birds fly faster in large flocks

Date: August 16, 2016

Source: Lund University

New research at Lund University in Sweden shows that the flight speed of birds is determined by a variety of factors. Among the most sensational is that the size of the flock has a significant impact on how fast the birds can fly. The larger the flock, the higher the speed.

Researchers at the Faculty of Science in Lund have now shown how several factors, working simultaneously together, determine the birds' flight speed. Their morphology, that is, the bird's weight and the shape of its wings, is one factor; wind direction and speed is another; and the situation (searching for food or travelling long distances) is a third.

However, what surprised the researchers the most was that the flock size has a major impact on the birds' speed.

"I was surprised that it is such an important factor. It has usually been neglected in studies of bird flight," says Professor Anders Hedenström who conducted the study together with Professor Susanne Åkesson.

This is the first time that researchers have successfully proven that the flight speed increases as the flock becomes bigger. The measurements were taken on the Swedish island Öland, where the researchers evaluated the birds' morphology and counted the number of birds in different flocks. Subsequently, with the help of an ornithodolite -- a measuring instrument that can be described as a telescope with a laser rangefinder that also records the speed and direction, as well as the height and side-angle of the wind -- they were able to measure the speed of various large flocks.

The result is clear: bigger flocks travel faster, no matter what species they belong to. What remains unclear is why. One theory is that in large flocks, there are more heavy birds, which fly faster than those that are lighter. In a large flock, it is easier to take advantage of the turbulence that occurs behind other birds, especially when flying in formation, like geese and other birds do. Utilising the turbulence makes it easier to maintain higher speed.

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