These Teen Birds Love Sleeping In, Too

A new study suggests young grassland songbirds postpone fledging in order to mooch off mom and dad as long as they can

smithsonian.com

We all know the early bird gets the worm, so why do these young endangered grassland songbirds hang out in their nests late into the day? A new study seeks to answer that question, and it could be that playing the waiting game is actually the best way for nesting siblings to get the most food before heading out on their own.

To some extent, teen birds are “kind of like [human] teenagers,” jokes Nicola Koper, a conservation biologist at the University of Manitoba in Canada and a co-author of the study published today in The Auk: Ornithological Advances. Rather than venturing out into the world to fend for themselves, hanging out in bed and chowing down on whatever food the adults bring home may be the most effective way to survive for adolescent humans as well as grassland birds.

But that’s about as far as the comparison goes—it’s hard out there in rural habitats for baby birds, and most don’t make it past a week, the study notes.

Because most birds’ homes are essentially roofless, cup-shaped twig collections, it’s long been assumed that young birds fledge, or leave the nest, during the day to avoid nocturnal predators. But that’s not the case for grassland birds, explains lead author of the new study, biologist Christine Ribic with the U.S. Geological Survey’s Wisconsin Cooperative Wildlife Research Unit. Out on the plains, the predators that threaten birds are often diurnal, and predation threats are high whether the avian youths are in the nest or out in the wild world.

“Basically, anything that moves in the grassland can kill those birds,” Ribic says. Even a frantic bunny rabbit can become a threat if it disturbs the nestlings and causes forced nest evacuations.

And natural predators aren’t the only threat to grassland passerines, commonly known as songbirds. Last year, the World Wildlife Foundation found that these birds are the most rapidly declining prairie-dwelling species in Canada. In the United States, grassland birds are disappearing faster than any other group of North American birds—along with their habitat. Understanding exactly what factors are most important to survival during this vulnerable stage in the birds’ life, such as depredation, parental motivation or obtaining enough energy, is critical to saving the species.

“Anything we can learn about the important transition from being inside to outside of the nest can help us understand a range of aspects of bird biology, including the development of independence in young birds and important life stages affecting bird populations,” says Thomas J. Benson, a wildlife biologist at the University of Illinois who was not involved in the study.

Of course, avian guardians do their best to find secluded locations to construct their happy homes and fiercely protect their young from danger, but there is only so much they can do when pretty much anything that “needs protein to live” is a threat to their survival, Koper says. (The team has footage of a cow gobbling up a chick straight from the nest and then coming back for seconds—and thirds.)

Because most nests are built in tough-to-spot locations, observing fledging behavior in the field has proven difficult. Even though people have been spying on birds for science and sport for decades, we actually know almost nothing about the vulnerable moment when a young grassland songbird leaves the nest for good.

To learn about this critical time in passerine development, the new study—a collaboration between three research groups—used footage collected by surveillance cameras to observe 200 grassland songbird nests in North Dakota, Minnesota, Wisconsin and Alberta. One of the teams involved in completing this new research, led by wildlife ecologist Pamela Pietz, has been filming nests since the 1990s. Back then, field researchers would wheel out a cart with a weatherproof car battery to power a 25-foot cable connected to a cube-shaped infrared camera, similar to convenience store security cameras.

But thanks to smaller and cheaper cameras and batteries, the teams were able to collect thousands of hours of footage and get an unprecedented look into the exciting lives of these grassland birds.

What they observed in the footage came as a surprise, Ribic says. Rather than departing the nest as early in the day as possible to maximize time to search for safety, the young birds stayed put well into the daylight hours. Some species, like the chestnut-collared longspurs, would sleep in past noon or all day, notes Koper. Others go in and out of the nest several times before finally committing to leaving.

In total, it even took some nests about two to three days for all the chicks in the nest to fledge. The researchers therefore believe that the chicks might try to mooch off their parents for food as long as possible to store as much energy as they can—carbo-loading like an endurance athlete—before finally leaving the nest.

Essentially, the birds were concerned with, “how do I get more food than my sibling, or hit my developmental threshold and brave the new world?” Ribic says.

Most theories about fledging are based on bird species that are easier to observe, such as birds that find a nook in a tree to nest or build cup-shaped nests in tree branches. It’s much more difficult to set up cameras with a clear view of nests in the clutter of thick, prairie grasses.

The team’s findings suggest that fledging motivation varies depending on nesting environment. Noting variation during such a critical transition into independence for these birds is crucial to devising effective conservation strategies, Koper says. For example, if we know that grassland birds depend on their parents right up until the moment they venture off on their own, then considering how humans interrupt or disturb that relationship with development projects is critical to slow the decline of the species.

Benson notes that there has been an increase in radio telemetry use to track songbirds after they fledge. He suggests combining the video-monitoring technique prior to fledging with radiomarking to get a full picture of what conditions lead to successful independence. “Following young birds outside of the nest would help us gain a better understanding of the implications of those decisions about when to leave the nest,” he says.

In the end, when and why birds leave the nest might be just as complicated as with humans—and sometimes, it might take a few tries.

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