Ask Kenn!

Ask Kenn Kaufman: Why Do Birds Abandon Nests for No Apparent Reason?

Also this month: How did Hawaii get its owls? And who is the best ear birder Kenn's ever met?

Who's Kenn? Simply put, Kenn is a national treasure. A renowned birder, author, and conservationist, Kenn Kaufman has spent his life dedicated to observing birds, reading about birds, writing about birds, and sharing the world of birds with others. With all that birdy knowledge in his brain, he also acts as the field editor for Audubon magazine. So, whenever we have a bird question stumping us around the office, we just ask Kenn. And now you can, too! If you have a bird or birding question you'd like Kenn to answer, leave them in the comments below or on Facebook. Maybe next month you'll get the kind of thorough, thoughtful, and even humorous response from Kenn we've grown so fond of over the years. —The Editors 

Why do birds abandon nests for no apparent reason?

One of the pleasures of summer birding is the chance to observe nesting activities of various species. Some birds may nest in relatively open situations, making it possible for us to watch from a respectful distance. If we happen to have a good vantage point on a visible nest—say, of American Robins, Mourning Doves, or Barn Swallows—it’s hard to avoid getting caught up in their family drama. We cheer them on, hoping the adults will succeed in fledging a brood of young.

The nesting season is a precarious time, with so many things that can go wrong to stymie the efforts of the parent birds. Sometimes the reasons for failure are clearly visible, such as when a nest is knocked down by a storm or destroyed by a predator. Sometimes predators remove the eggs or young without damaging the nest, and that can be hard to detect if we don’t see them in the act. Other times, though, the parent birds seem to simply abandon their nests, and the reasons may be obscure.

Of course, most bird nests are just temporary shelters for the eggs and the hatchlings. The young birds will leave the nest as soon as they can, and in most cases, especially with smaller species, that same nest will never be used again—the parents will build a new one for the next brood. So when adult birds abandon a nest, it doesn’t necessarily mean they’ve left the area. 

The roles of parent birds vary widely among species. In hummingbirds, the female does it all—builds the nest, incubates the eggs, feeds the young—and there’s no reason for the male to stick around. But in many birds, both parents participate in these duties. If one parent dies, the remaining one may succeed in raising at least some of the young, but in other cases the surviving parent simply abandons the attempt.

Abandoned nest. Photo: Ray A. Akey/Alamy

Weather can have a significant impact on nesting success. In unusually cold or rainy conditions, if parent birds have difficulty finding enough food for themselves while there are eggs in the nest, they may be off the nest too much for effective incubation. If such conditions strike after the eggs hatch, the parent birds have the added challenge of finding food both for themselves and for the nestlings. In either situation, the adults may wind up abandoning the nest altogether.

In most places in this summer of 2020, nesting birds didn’t have to contend with unusual cold, but exceptional heat could have been a problem in some areas. I haven’t seen many studies on how heat could affect the nesting activity of typical songbirds, but I wonder if the impact could be as much psychological as it is physical. After all, humans can feel listless, irritable, and unmotivated when the weather is too hot. We can’t assume that birds have human emotions, of course, but we also shouldn’t think of them as little robots with feathers. I can easily imagine that a bird suffering from too many too-hot days might give up on the instinct to breed or raise young, and just go off to take care of itself.

How did Barn Owls and Short-eared Owls end up all the way over in Hawaii?

If you travel halfway across the widest ocean in the world and arrive in Hawaii, you might not expect to see owls living there—especially not owls that are also found in North America and Eurasia. But it’s true: Barn Owl and Short-eared Owl are both widespread in the main Hawaiian Islands.

These two are not close relatives—in fact, Barn Owls are classified in a separate family from typical owls—but both have wide distributions around the world. More importantly, both live in open country. Owls in forest habitats typically hunt by waiting and watching from a perch and then swooping down on prey. Out in wide-open fields and marshes, Barn Owls and Short-eared Owls hunt by flying continuously, low and slow over the terrain, watching and listening for prey below. Strong and sustained flight comes naturally to them, so it’s no surprise that they can disperse long distances.

Short-eared Owls undoubtedly arrived in the Hawaiian Islands under their own power. These owls of open country are among the most widespread bird species in the world, breeding across North America, Europe, Asia, and much of South America. They’ve also managed to colonize many islands or island groups. In the Atlantic, those include Iceland, the Azores, the Falklands, and many islands in the Caribbean. In the Pacific, in addition to Hawaii, Short-eared Owls are also resident on the Galapagos, the Caroline Islands, and the Philippines. The residents in Hawaii have been there long enough to have evolved their own distinctive appearance, so they’re now classified as a distinct subspecies.

Although we may not think of owls as flying long distances across the ocean, the owls apparently have other ideas. In the northwestern Hawaiian Islands, away from the main islands occupied by the resident subspecies, migrant Short-eared Owls of the subspecies from Asia or North America have been recorded many times. So the population in the main islands clearly could have been founded by migrants that arrived from the north and then stayed.

The interesting thing is that those resident Short-eareds may have arrived within the last 2,000 years. Fossil and subfossil remains of birds have been studied extensively in Hawaii, and very few remains of Short-eared Owls have been found among them. Some scientists believe these owls didn’t become established until after humans arrived in Hawaii from Polynesia. The timing of human arrival is debated, with a range of suggested dates between 100 and 1100 A.D.; but when they did arrive, apparently they brought Polynesian rats with them. Those rats, and other introduced rodents, are the main prey for Short-eareds in Hawaii today, so it’s possible the owls couldn’t become established until humans brought in these convenient prey animals.  

Hawaiian Short-eared Owl. Photo: Kelly Hetrick/Audubon Photography Awards

That doesn’t mean the arrival of humans in Hawaii was good for birds in general. The same studies of subfossil remains also suggest that several native birds went extinct after the Polynesians arrived—including four species of endemic owls. These birds, the stilt-owls of the genus Gallistrix, were long-legged predators that lived on the ground and apparently fed mostly on birds. Their ancestors must have arrived on the islands in the very distant past, to give them time to evolve such distinctive features. But when humans brought in rats, pigs, and other mammals, these terrestrial owls rapidly disappeared.

And what about the Barn Owl? It seems logical to picture this species having colonized Hawaii on its own. After all, it’s one of the most widespread owls in the world, native to six continents and to various oceanic islands including Fiji, the Galapagos, and the Canary Islands. But in Hawaii, it was intentionally introduced by humans to try to control rodents in farmland. During the late 1950s and early 1960s, Barn Owls were brought from zoos on the U.S. mainland, and the species quickly became established. Today they are found in many of the same open areas as Short-eared Owls on the main islands. So both of these owls apparently had human aid in getting established in Hawaii, but in very different ways.   

Of all the birders you’ve met, who do you think was the best at birding by ear?

Most of us start with a visual approach: We are bird WATCHING. But identifying birds by their songs and calls, or birding by ear, becomes more and more important as we gain experience. Beyond a certain point, we’re likely to find and identify the majority of birds by sound.

Learning the voices of birds is always a personal challenge, but the resources available to help are far more abundant now than they were a few decades ago. When I was a kid in the 1960s and 1970s, I had a few records—Peterson’s Field Guide to Bird Songs album, Irby Davis’s Mexican Bird Songs—that I played over and over, but they included only a few species. Today, you can listen to the voices of practically every North American bird in Audubon’s free bird guide app, and hear numerous recordings of most of the world’s bird species at online sites like Xeno-Canto or the Cornell Lab of Ornithology’s Macaulay Library. There are also plenty of guides and tutorials available online.

The importance of sound varies with habitat. If we’re scanning ducks on a winter lake, we can operate mostly by sight (while listening, of course, in case something like a flock of redpolls flies over). Deep in the forest, sound becomes more critical. This is especially true in dense tropical forest, where there are usually more bird species and they’re usually harder to see. At some places in the western Amazon Basin, more than 500 bird species may occur in one square mile of forest. In a day there you might hear 300 of those species, but it would be an extreme challenge to see half that many. Without knowing the voices, you really can’t get a sense of what’s around you.

As you might have guessed from the preceding, my candidate for greatest ear-birder is someone who reigned supreme on identifying voices in the American tropics: the late Theodore A. Parker III.

I met Ted Parker in 1972, when we were both teenagers, and I birded with him on some of his first trips into Mexico. It was fascinating to see his level of concentration in sorting out these birds on the edge of the tropics. At first he was writing detailed notes on bird voices, but he soon graduated to recording them. From 1974 until the time of his death in 1993, Ted spent more than half his time in the field in South America and Central America, on expeditions with Louisiana State University (LSU) and as a leader of birding tours. During that time, he worked tirelessly on tracking down as many birds as possible and getting high-quality recordings of their voices. Back at LSU between trips, he would spend hours studying the tapes, noting subtleties and making comparisons. He probably knew more than 4,000 species by voice, and ultimately he would contribute more than 10,000 separate recordings to the sound library at Cornell.

This ear-birding skill was not just for show. In later years, Ted developed a method of rapid biodiversity assessments for Conservation International, and did surveys in sites from Belize to Bolivia. Many of these surveys led directly to the preservation of key habitats. The studies wouldn’t have been possible without his ability to recognize every bird he heard.

So was he the all-time greatest in sheer skill? Direct comparisons would be impossible, and not very meaningful. Mark Robbins, one of Ted Parker’s closest friends, has now contributed more recordings to Cornell than Ted did. Bret Whitney probably knows more different bird sounds now than Ted did at the time of his death; Bret has found several species new to science by going into a new area and hearing a bird he didn’t recognize. And in this expanding field there are undoubtedly other experts today who could at least approach Ted at the peak of his powers.

But I would still give the edge to Ted Parker because he did so much of his work when so little was known. Birders starting out in the tropics today have the advantage of a vast amount of collected knowledge. In addition to modern field guides and photos, they can instantly access tens of thousands of audio recordings, many contributed by Parker himself. Ted’s knowledge was gained through years of steadfast work in the field, through an extraordinary level of focus and dedication, and I don’t think I’ll ever see anything more impressive.

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Have a bird or birding question for Kenn? Leave it in the comments below, and maybe he'll answer it in a future column.  

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