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.)
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)
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!
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
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)
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.
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.
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.
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.
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?
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.
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.
“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.
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.