It isn’t easy to watch as parasitic fledgling cowbirds run their adopted Song Sparrow parents ragged as they relentlessly follow the sparrows around and beg for food.
For the past several weeks at one of my favorite birding spots in the mountains fledgling cowbirds begging for food from their host species parents has been a very common occurrence. At this location the host species has nearly always been Song Sparrows.
These first three photos were taken three days ago in rare moments when the young cowbirds weren’t hounding their adoptive parents for food. Most of the time the cowbird fledglings would follow the Song Sparrow adult everywhere it went and they were relentless about begging for food, to the point that I had great sympathy for the sparrow who had to be exhausted.
Here it may look like it’s the sparrow doing the begging but that’s not the case – it was just turning on its perch.
The sparrow turned its back on the young cowbird who seemed to sense that there would be no food for the time being so it briefly relented in its begging.
Given the situation I have no idea what this poor Song Sparrow had to sing about. Perhaps it was singing the blues.
The very next day and at the same location where these first three photos were taken I documented (poorly) the ultimate source of cowbird parasitism.
Cowbird sex.
I noticed the female on top of the tree displaying solicitation behavior so I fired a burst in hopes I’d get the male coming in to mate with her. This is the best photo I managed to get, the actual mating shots didn’t turn out well at all.
Brown-headed Cowbird brood parasitism:
- As brood parasites female cowbirds lay their eggs in the nest of another species for the host species to brood and provide care for their young.
- Cowbirds never build their own nests.
- Cowbirds never develop brood patches, despite normal levels of the hormone that induces brood patches in other species.
- Host species adults always feed parasitic cowbird fledglings more food then they do their own fledglings.
- In areas where both species occur Song Sparrows are a favorite host for Brown-headed Cowbirds. I’ve also seen cowbirds parasitize significant numbers of Savannah Sparrows.
- Cowbirds are known to parasitize 144 host species ranging in size from 10 gram creepers, kinglets and gnatcatchers to 150 gram meadowlarks.
- Research suggests the most deleterious effect of cowbird parasitism on their host species is nest destruction. Cowbirds destroy nests that are otherwise unavailable for parasitism because of late incubation, young nestlings etc., which forces the potential hosts to build new nests that can then be parasitized. In effect cowbirds are “farming” their host species.
When I photographed the mating cowbirds I tried to look at the bright side. If cowbirds are still mating in the latter part of July it suggests that their host species, various kinds of songbirds, are still in the early stages of a reproduction cycle too.
For all of us who love birds that’s a good thing.
Ron
Note: I’ve taken many photos of fledgling cowbirds actually chasing Song Sparrows and begging for food at this location. But the birds have usually been far away on the muddy streambank and because of depth of field issues at least one of them has typically been soft so I haven’t included any of those photos today.
Fantastic photos!
Teaching hindsight is always 20/20! Just glad I had enough Natural History experience to take my class on field trips, but boy do I wish I had had some of these kind of photos too!
Great photos. Good things it isn’t a Coot raising the young birds.When they practice parasitism, the adult will kill the young that don’t belong to them. I read that despite being raised by another species, Cowbird fledglings have no problem learning their own species’ songs. because they leave their nests at night to spend time with their own species from about 20-25 days old, but there are cases when the young spend too much time with the host families and learn their songs. Apparently the parents leave the fledglings in the care of the foster parents but keep a close eye on them to see which birds raise their young well. Ha,I guess they keep busy eating flies off the bisons and cows. I got this information from the Audubon site which showed a Warbler feeding a young cowbird. Fascinating!
It is SOOOO hard not to villainize brood parasites like cowbirds. I know that it’s an evolutionary adaptation, but I still feel so sorry for the smaller “stepparents” who are busting their tail feathers.
Wish I had some of your photos when I was still teaching this stuff. These are much better than anything that came with our textbooks.
Ha, I wish I had some of my photos when I was teaching too, Marty. Big time!
Very interesting post this morning. I am always amazed at nature.
Thank you, Betty.
Whinging, complaining, demanding youngsters often make me feel for the parent – whatever the species (of either parent or the complainer).
Thank you Ron, and particular thanks to Dan who told me something I hadn’t known.
It is not yet 5am here and I have already learned something – a most excellent start to the day.
Thanks, EC. I often learn now things from Dan. We’re lucky to have him around.
It’s all too easy to make moral judgements about nature and cowbirds have often been demonized by well-respected naturalists and ornithologists of past centuries. But I find cowbirds fascinating in many respects. Approximately 1% of the world’s bird species exhibit brood parasitism. Many have very specific hosts and a few, like our cowbird are generalists, using many other species as hosts. For the Brown-headed Cowbird it makes sense. They follow bison (hence the name cowbird) and feed on the insects disturbed by their hooves. But following bison means they travel many miles every day and have no opportunity to build a nest and return to incubate eggs or feed young. Thus, a lifestyle of brood parasitism evolved in this species. There are many fascinating behaviors that can be observed in cowbirds but most people don’t bother to look, allowing their feelings of dislike to get in the way. I encourage everyone to set aside your ethics (which are a human construct) and allow yourself to be fascinated as nature as it is. I think you will find rewards in so doing.
Thank you Dan. That was something I hadn’t known – and you are right it is fascinating. As a survival adaptation it makes a heap of sense.
I agree, they’re fascinating birds Dan. And they’re a native species and brood parasitism is a natural behavior. But I still find some of the things they do hard to watch.
You are so right. It’s hard to stay unemotionally attached sometimes. We once had a pair of California Scrub-Jays build a nest in the bushes just beyond our window. We couldn’t see the nest but we watched the adults come and go and could easily hear the young once the eggs hatched. Just days before fledging, a Cooper’s Hawk also found the nest and killed and removed the young. It’s perfectly natural and hawks need to eat too, but in this case, it was “our” jays that we had watched since the adults began nest-building. It was definitely hard to see happen.
I once saw a Scarlet Tanager feeding a Cowbird. Soul-crushing experience.
I’m not surprised, Diane.
Wonderful photos! I feel empathy for the poor song sparrow, those big babies never stop screaming.
You know very well what it’s been like at that spot recently, April. I think it borders on pathetic.
That’s a beautiful shot of the male Brown-headed Cowbird, albeit missing a flight feather. It’s near impossible not to anthropomorphise all kinds of bad things about them. A Kinglet sitting on a Cowbird egg. Hard to imagine how that works.
“A Kinglet sitting on a Cowbird egg. Hard to imagine how that works”
I know what you mean, Lyle. It brings up quite a visual doesn’t it.
Strange adaptations to keep a species going – must not put much of a dent in the species being tricked into caring for the young cow birds or there wouldn’t be any to fill the roll! 😉
Between wind and bull snakes Robins aren’t doing well this year getting young raised here…….
Judy, I think they do put a significant dent in the numbers of some species, particularly those with small populations like some warblers. I keep reminding myself that it’s a natural relationship so I shouldn’t think less of cowbirds for doing what they do…