Category Archives: Bird Behavior

Cuckoo Mimicry, Back and Forth

Adult common cuckoo (photo from Wikimedia Commons)

As a brood parasite, the common cuckoo (Cuculus canorus) gets away with laying its eggs in other birds’ nests because it’s larger and uses mimicry to fool its hosts.

Our own brood parasite, the brown-headed cowbird, uses stealth to dump her eggs but a female cuckoo doesn’t have to be sneaky. She looks like a sparrowhawk, the Eurasian version of our sharp-shinned hawk, so naive songbirds scatter when she shows up.

Also, her eggs closely mimic those of her favorite hosts: dunnocks, meadow pipits, and reed warblers. Here are four clutches of reed warbler eggs with a single cuckoo egg laid in each. The cuckoo egg is quite similar though larger. (Check yesterday’s blog for photos of a reed warbler and meadow pipit feeding cuckoo chicks.)

Four clutches of reed warbler eggs parasitized by a single (larger) common cuckoo egg (photo from Wikimedia Commons)

While the cuckoo mimics features of other birds we mimic him. Here’s a real cuckoo calling…

… and our mimicry of the cuckoo in a Black Forest cuckoo clock.

Cuckoo mimicry back and forth.

(photos from Wikimedia Commons; click on the captions to see the original)

If You Think Cowbirds Are Bad …

Just like brown-headed cowbirds (Molothrus ater), common cuckoos (Cuculus canorus) in Eurasia are obligate brood parasites that never raise their young. Cuckoos lay their eggs in the nests of smaller birds that foster the cuckoo chicks as their own. A stark difference between cowbirds and cuckoos, though, is their size. Cuckoo chicks can be 10 times larger than their hosts!

Compare the Eurasian reed warbler (Acrocephalus scirpaceus) feeding a common cuckoo chick, above, to the brown headed cowbird chick with its song sparrow (Melospiza melodia) foster parent below.

Brown-headed cowbird chick begging from song sparrow host (photo from Wikimedia Commons)

The cowbird is slightly larger than its host but the cuckoo chick when it leaves the nest will be 10 times the reed warbler’s weight.

This situation can be even more bleak, as shown in a Twitter post by John Deakins.

So if you think cowbirds are bad, consider the foster parents of common cuckoos.

p.s. I wish I knew the identity of the foster parent standing on the chick’s back. Can any of you identify it? I believe the photo was taken in the UK.

UPDATE: Janet Campagna suggests meadow pipit, in which case the young cuckoo is 6 times the weight of the foster parent.

(photos from Wikimedia Commons plus an embedded photo from Twitter; click on the captions/tweet to see the originals)

What’s That Whining Sound?

Juvenile red-tailed hawk, Washington DC, 2017 (photo from Wikimedia Commons)

Have you heard whining that sounds like this?

Sometimes you hear songbirds calling nearby, “Danger! Watch out!”

In July and early August young red-tailed hawks whine for food. Here’s one in July 2018 at New York’s Botanical Garden with an American robin raising the alarm.

And here’s one on a windowsill in Austin, Texas, July 2011.

Red-tailed hawks raise one brood per year. The female lays eggs in March or April. The eggs hatch in 28-35 days and the young fledge 42-46 days later. That’s when the begging begins.

For three weeks juvenile red-tailed hawks depend on their parents and are not shy about asking for food. Whine!

The whining doesn’t end there. Though the youngsters become increasingly self sufficient they still want a handout if they can get one. Whine! Whine! Whine! Their parents ignore them.

Self sufficiency is the first big hurdle on their way to becoming successful adult red-tails. Some youngsters take longer than others to get the hint.

Meanwhile, whine, whine, whine, WHINE!

(photo from Wikimedia Commons; click on the caption to see the original. Audio from Xeno Canto, videos from YouTube)

Mixed Up Ducks

Mixed up ducks in Germany (photo from Wikimedia Commons)

One of the challenges of city birding is identifying the mixed up ducks not found in any field guide. These “mutt ducks” are the hybrids of mallards paired with escaped domestic ducks.

It’s easy for domestic ducks to hybridize with mallards because nearly all of them(*) are descended from mallards (Anas platyrhynchos).

Mallard cross with a domestic duck (photo from Wikimedia Commons)

Mallards hybridize with wild ducks, too, as shown in this a mallard X gadwall mix.

Mallard X gadwall hybrid Brewer’s duck (photo from Wikimedia Commons)

Some ornithologists worry that mallards will hybridize their closest relatives — American black ducks, Mexican ducks and mottled ducks — out of existence, as in this mallard X Mexican duck mix.

Mallard X Mexican duck hybrid (photo from Wikimedia Commons)

But perhaps they’re forgetting how recently those species evolved from mallards. The Mexican duck (Anas diazi) that occurs in Mexico and the U.S. Southwest was thought to be a subspecies of mallard until 1957.

Mallards are just working on creating new species. 😉

Read more about mixed up ducks in this vintage article: Ugly Ducks

(*) Some domestic ducks are descended from Muscovy ducks.

(photos from Wikimedia Commons; click the captions to see the originals)

Last Round of Cowbird Babies

Brown-headed cowbird youngster begs from a song sparrow foster parent (photo from Wikimedia Commons)

On a late July visit to Washington’s Landing (Herr’s Island) I saw two song sparrow families with begging fledglings. Unfortunately the begging youngsters were brown-headed cowbirds, not song sparrows.

Female brown-headed cowbirds lay their eggs in the nests of smaller birds.  Each cowbird chick is raised, not by its own mother, but by foster parents of another species. To make matters worse, cowbird parents lurk near the foster nest to make sure their own baby survives. They remove the host’s eggs or kill the foster parents’ young to give their own chick a better chance.

Cowbirds parasitize many species but are especially fond of song sparrows and yellow warblers. Yellow warblers are well aware of cowbird eggs and will “abandon” the nest by building a new nest on top of the old one. Experienced song sparrows get upset but don’t have an immediate solution.

However, song sparrows have a secret weapon — their breeding season is longer. Their first of two to four broods may begin before cowbirds are ready to lay eggs while the last nest starts after cowbirds are done.

In Pennsylvania brown-headed cowbirds stop laying in early July while song sparrows are still going strong. What I saw at Washington’s Landing was this year’s last round of cowbird babies.

(photo from Wikimedia Commons; click on the caption to see the original)

The Threesome Continues

27 July 2020

Last Friday Mary Ann Pike noticed that Terzo and Morela were spending a lot of time at the Pitt peregrine nest and commented:

Seems like Morela and Terzo have been swapping shifts at the nest today. I saw Morela this morning, then Terzo early afternoon for a while, now Morela is there again. What a strange situation with Ecco in the mix. I wonder if he hangs around Oakland somewhere when he’s not on camera. It seems like the other 2 must be spending most of their time in Oakland but under normal circumstances they wouldn’t let a third Peregrine hang around.

Mary Ann Pike, 24 July 2020, 4:33pm

We didn’t realize it on Friday but Terzo and Morela were probably vigilant because Ecco was nearby. He appeared on camera before dawn.

In the video below Ecco arrives at 5:33am to bow with Morela. After he leaves Morela pauses for 45 seconds, then we hear a peregrine wailing at 3:28 in the video. The wailing continues intermittently over the next three minutes. Was it Terzo complaining that Ecco was there?

The rest of 24 July was very busy. Morela and Terzo bowed at 8:30a and 3:30p.

Morela and Terzo court, 24 July 2020, 8:30am

Terzo sunbathed and watched for two hours.

Then Morela hung out and preened for three hours. I’m happy to see that Morela’s flipped primary feather is gone.

Terzo and Morela courted at dawn on Sunday morning. There was no sign of Ecco but I’m sure he’ll return.

However, the threesome continues at the Pitt peregrine nest.

(photos and videos from the National Aviary falconcam at Univ of Pittsburgh)

p.s. The National Aviary falconcam streaming service ends on 31 July 2020. It will resume next February.

Who says birds can’t change their tune?

White-throated sparrow (photo from Wikimedia Commons)

Songbirds are born with the ability to sing but perfect their songs by listening to others. Many learn when immature, usually from their fathers, and then don’t change their tunes. That’s why it was a surprise when Ken Otter and Scott Ramsay discovered that a new song from western Canada is so popular among white-throated sparrows that it’s taking over the country.

White-throated sparrows (Zonotrichia albicollis) learn their songs at 30 to 100 days old and don’t vary them later except for a window in the birds’ second winter when they’re open to new ideas.

Twenty years ago all the birds sang the tune we still hear in the East, “Oh sweet Canada, Canada, Canada.” The end of the song is a triplet of three syllables.

In the early 2000s Otter and Ramsay recorded a new song unique to Prince George, a remote city in northern British Columbia. The birds sang “Oh sweet cana, cana, cana” without the final syllable.

Fast forward 20 years. Otter and Ramsay watched as “Oh sweet cana, cana, cana” moved east and gained traction across Canada. By 2017 the new song was the only one in the west and was sung by half the white-throated sparrows in Ontario.

It spreads during the winter. White-throated sparrows from across Canada spend the winter together in Oklahoma, Arkansas, Kansas and eastern Texas where mature birds demonstrate their favorite tunes.

The new song caught on rapidly with the younger crowd, probably because the ladies prefer it. Who says songbirds can’t change their tunes?

Read more at The Atlantic’s The Birdsong That Took Over North America.

(photo from Wikimedia Commons; click on the caption to see the original. Audio embedded from Xeno Canto)

Young Raptors As Home Wreckers

Immature bald eagle, March 2015 (photo by Steve Gosser)

Something is happening among nesting bald eagles in the James River watershed that may explain what we’re seeing among peregrines in western Pennsylvania. There are lots of eagles at the James River but less nesting success than in the past. The Center for Conservation Biology in Williamsburg, Virginia has figured out why.

CCB has been conducting bald eagle nesting surveys every March since the 1970s. Seven years after DDT was banned they found only one pair of bald eagles in the watershed. This year there are 319 pairs.

Meanwhile, “eagle productivity has dropped as the population has grown and breeding density has increased.” The number of eaglets per nest peaked at 1.6+ in the mid 1990s but has dropped to only 1.05 today.

Lower nesting success is not a food problem, it’s a competition problem. CCB explains:

The mechanism causing the decline does not appear to be traditional resource competition where pairs scramble for their share of limited fish. Rather, the mechanism appears to be young marauding eagles that are disrupting territory holders and competing for a limited set of viable breeding territories.

Young bald eagles are harassing adult pairs in an attempt to gain a territory — so much so that some pairs fail to nest successfully.

Adult and immature bald eagles jousting (photo by Steve Gosser)

This sounds like what happened at the Cathedral of Learning peregrine nest this year. In February a young male, Ecco, showed up at the Pitt nest and persistently vied for the site — so much so that Morela didn’t lay eggs until May and her eggs were never incubated. Hmmmm.

Young bald eagles are home wreckers. Maybe young peregrines are, too.

Read more about the James River bald eagle population at CCB’s James River Eagle Population Continues to Soar While Productivity Continues to Fall.

(photos by Steve Gosser)

Partners For Life?

Bewick’s swans at Big Waters, UK (photo from Wikimedia Commons)

“Birds are classically among the most monogamous of all organisms,” wrote Frank B. Gill in his textbook Ornithology.     90% of bird species form a pair bond in which they commit to work together to raise their young. Mammals are famously poor at this. Only 5% of mammalian species form pair bonds. Humans are among the few.(*)

For many years, ornithologists thought that birds were both sexually and socially monogamous but DNA studies have shown there is not always a sexual commitment. Extramarital copulations occur but they don’t dissolve the social bond. For instance, this happens among chickadees and …

Between one in 10 and one in three eggs in a female cardinal‘s nest has genes that don’t match her partner, and less commonly, they don’t even match her own. But because of that pair bond to rear the young, they are considered socially monogamous.

Bird Watcher’s Digest: Do Birds Mate For Life?

Even social monogamy comes in a range of time spans depending on the species. Avian pair bonds may last for one nesting, for one season, or for a lifetime.

Those who mate for life include Bewick’s swans (above), wandering albatrosses (pictured below), blue jays and barn owls (videos).

Wandering albatross at Macquarie Island (photo from Wikimedia Commons)

Other lifelong pairings include Canada geese, bald eagles, peregrine falcons, red-tailed hawks, ravens, scarlet macaws, sandhill cranes and many more.

But as I said, social monogamy among bird species is a spectrum from lifelong to short commitments. Humans are like this, too.

In the U.S. the human divorce rate is 40%. There’s a bird with the same track record. The masked booby.

Masked booby pair (photo from Wikimedia Commons)

(*) p.s. Here’s why humans started forming pair bonds: Humans evolved monogamous relationships to stop men killing rivals babies

Song Sparrow Babies At The Nest

Song sparrow nestlings and parents, 12 July 2020 (screenshot from Bob Donnan video)

17 July 2020

This month a pair of song sparrows is nesting in a hanging basket above Bob Donnan’s deck in southwestern Pennsylvania. Bob wanted to see them better without disturbing them, so he set up a nest camera and is publishing YouTube videos of their activity. This week the babies grew a lot.

Bob’s 12 July 2020 video opens with both parents feeding four nestlings. Only about three days old, the nestlings are featherless and their eyes are closed. After the feeding ‘papa’ bird leaves while ‘mama’ remains to tidy the nest. She picks up something that looks like a worm and eats it — a fecal sac from one of her nestlings.

Later we hear ‘papa’ sparrow singing in the background while ‘mama’ shelters her young and appears to pant. It’s hot. Bob has been trying to provide extra shade because the sparrows’ air traffic has made the flowers droop. (Click here or on the screenshot at top to see the 12 July video.)

Three days later, 15 July, the babies are growing fast. The three remaining nestlings jump up to feed when mama arrives. They look so tall! Click on the image below to see Bob’s 15 July video.

Song sparrow nestlings, 15 July 2020 (screenshot from video by Bob Donnan)

Song sparrows babies mature so fast that they leave the nest at only 10 days old, even earlier in the heat of summer.

The nest on Bob’s deck will be empty soon. You have to look quickly to see song sparrow babies at the nest.

p.s. Bob has a great selection of “how to” landscaping videos on his Bobscaping YouTube channel.

Follow-up videos: (18 July) Junior! Get Back in the Nest!

(screenshots from videos by Bob Donnan; click on the images to see the videos)