Latest news with #MacChamberlain
Forbes
3 days ago
- Science
- Forbes
Young Cowbirds Look To Adult Females For Proper Social Development
Raised by foster parents, how do juvenile cowbirds discover their true identity and learn proper social development so they grow up to be normally functioning adult cowbirds? Most birders don't much like cowbirds because the adults lay their eggs in other songbirds' nests and abandon them to be raised by their foster parents, often at the expense of the foster parents' own offspring. This life history trait is known as obligate brood parasitism. 'Cowbirds often get a bad rap because they're brood parasites,' the study's lead author, behavioral ecologist Mac Chamberlain, a PhD Candidate at the University of Illinois Urbana-Champaign, told me in email. 'But it's exactly this unusual start in life that has pushed them to evolve some remarkably creative strategies to navigate the world,' Mr Chamberlain explained in email. 'Less than 1% of all bird species in the world are brood parasites, with cowbirds being the only obligate brood parasite bird group in North America. Rather than seeing them as villains, we should start recognizing cowbirds as a powerful example of how nature comes up with clever and unexpected ways to solve tough problems.' Upon hatching, most young birds imprint on the first moving being they see and view that particular being as their parent. So how do juvenile Brown-headed Cowbirds, Molothrus ater, who probably have never seen their parents, discover their true identity and learn proper social development so they grow up to be normally functioning adult cowbirds? A recent study led by Mr Chamberlain finds that fledgling cowbirds specifically seek out and follow adult female cowbirds. These adult females appear to be mentoring the juveniles in the complex social art of being a proper cowbird, acting as role models for how to find food, proper mating behaviors, and how to protect themselves from predators so they can join the adult flock. But what is it about adult female cowbirds that is so attractive to these juveniles? First, female cowbirds' plumage is more similar in appearance to the juveniles than to that of the more aggressive male cowbirds, which probably partially explains why the young birds seek them out. In addition to similarities in appearance, the young cowbirds are drawn to the chattering noises of adult female cowbirds (read more here). 'All cowbirds hatch with a built-in attraction to the female 'chatter' call,' Mr Chamberlain told me in email. 'This call acts like a homing beacon, helping the juvenile cowbirds find others of the same species. Even without learning it, they recognize that sound as something familiar. Lab-raised cowbirds also tend to gravitate toward birds that look like them. Lastly, as the young cowbirds grow up and begin to resemble adults, other bird species will start showing more aggression towards them. Between the sound, the visual cues, and the social pressure they receive from different species, young cowbirds are highly motivated to seek out the safety and familiarity of their own kind.' The study suggests that the young cowbirds may be specifically seeking out adult cowbirds with female characteristics with no preference, or perhaps no knowledge, of whether they are related. 'What surprised me was how clearly the juveniles in the wild showed a preference for adult females,' Mr Chamberlain said in email. 'This lines up with what lab studies have suggested, but with only seven juvenile birds in our sample, I didn't expect the pattern to be so strong. It's uncommon to see such a clear signal in the wild with such a small group, which makes the result all the more exciting.' How did the team figure out that juvenile cowbirds are attracted to adult females of the species? Over a period of three years, they captured 122 cowbirds in total and used DNA testing to identify both the sex of captured juveniles and to determine whether the captured adult-juvenile pairs were related to each other. In fact, they found that only 2 of the 7 juvenile cowbirds were captured along with a relative. Despite the fact that the population is comprised mostly of adult males, the juvenile cowbirds were much more likely to be captured in the company of adult females. These results suggest that the young cowbirds may be specifically seeking out adult cowbirds with female characteristics with no preference, or perhaps no knowledge, of whether they are related. This study's findings are contrary to earlier findings which indicated that captured adult-juvenile pairs were likely to be related. That said, the sample was very small and did not include all potential parents in the population, so it must be replicated with much larger numbers to determine whether relatedness plays any role in the social development of cowbirds. Are there plans to follow up, or perhaps to study juvenile cowbirds' social interactions with adult males? 'At the moment, we don't have plans to continue this work, but it's a question that definitely deserves more attention,' Mr Chamberlain replied in email. 'Juvenile cowbirds likely continue to learn and refine their social behavior well into the fall and through their first breeding season. Understanding how they interact with adult males during that period could fill in some big gaps. Tracking specific individuals across those critical stages would help us see how early experiences shape their social development and how those relationships unfold over time.' Source: Mac L. Chamberlain, Wendy Schelsky, Autumn Bush, Shanelle Johnson-Cadle, Shelby Lawson, and Mark E. Hauber (2025). Adult sex dictates juvenile-adult interactions in brood-parasitic brown-headed cowbirds, Molothrus ater, Animal Behaviour, 226:123247 | doi:10.1016/ © Copyright by GrrlScientist | hosted by Forbes | Socials: Bluesky | CounterSocial | Gab | LinkedIn | Mastodon Science | Spoutible | SubStack | Threads | Tribel | Tumblr | Twitter
CBC
06-07-2025
- Science
- CBC
These bird moms lay their eggs in other species' nest, and never come back for them
When a female cowbird is ready to have a baby, she'll stake out another bird's nest, wait until the coast is clear, then slip in, stealthily lay her egg and leave it behind for another family to raise. Most other baby songbirds in that situation would imprint on their adoptive mothers and grow up believing they were members of another species. Cowbirds, however, have no such identity crises. "It's very clear that at a certain age they get very tired of their host parents and they want to get out of town," Mac Chamberlain, an ornithologist at the University of Illinois Urbana-Champaign, told As It Happens. Previous research suggested that once the chicks were reared, their biological mothers would come back for them and teach them how to be cowbirds. But a new study, published in the journal Animal Behaviour, found that's not the case. While they do eventually find other members of their own species, they get along just fine without mom. Brood parasites Cowbirds are what's known as brood parasites, meaning they allow other species to rear their young, often to the host nest's detriment. Some birds are clever enough to recognize an unfamiliar egg in their midst and get rid of it. But once the cowbird hatches and starts squawking for food, most mothers will instinctively feed them, none the wiser of the deception. Less than one per cent of bird species worldwide use this mating strategy, Chamberlain said. "It's very cool and it's very novel, I think, compared to other birds," he said. Some brood parasites, like cuckoo birds, go on a killing spree the minute they hatch, pushing their host siblings out of the nest to their untimely deaths so they don't have to compete for resources. "Cowbirds are unique in the fact that they're nest sharers," Chamberlain said. "The only harm they really do to their nest mates is just being an extra mouth to feed." While not as brutal as cuckoos, it's still not great for the host family. "Cowbirds hatch earlier and start begging, many have argued, more frequently and more intensely [than their nest mates], and so they end up getting more food," Matthew Louder, a former scientist who studied brood parasites at Texas A&M University, told CBC. "If you cannot bring enough food to feed your other ones, you might lose some of the other offspring." If they reunite with mom, it's probably random chance Within about a month, the little imposters leave the nest for good. From there, Chamberlain says they have a short window to find an adult cowbird and learn the ropes before grouping together to migrate south. It's not clear what happens if they don't find an adult in time, but Chamberlain says cuckoos who fail in this quest never learn their species-specific behaviours and local dialect, and end up ostracized from their flock. In a 1995 study, researchers found and trapped pairs of adult and juvenile brown-headed cowbirds, sampled their blood, and discovered many of these duos were related. The authors theorized the juvenile cowbirds were reuniting with their mothers before flying south. The mothers, they suggested, may even keep watch over their hatchlings from afar, then lead them out of the nest when it's time. But this latest study was not able to reproduce those findings. Researchers spent three years capturing and genetically testing brown-headed cowbirds — 122 adults and seven juveniles altogether — and found the young birds were more likely to be found with unrelated female adults. Scientists believe the juveniles find and latch onto adult females, in part, because they have similar looking plumage, but also because they're instinctively drawn to their chattering calls. Louder says he was not surprised by the findings. In his own research, he says he'd already shown that juvenile cowbirds leave their nests all on their own. But Chamberlain says this doesn't mean the 1995 study was flawed. This new research, he says, was conducted in Illinois, where cowbirds are more populous than on the east coast, where the previous study was carried out. "If you're .... in an area where there's only really one breeding female cowbird, if you bump into a female cowbird, it's likely going to be your mom," he said. Stephen Rothstein, a professor emeritus at the University of California Santa Barbara who wasn't involved in the study, says while the methodology is sound, the sample size of juveniles is too small to draw any hard conclusions. Nevertheless, he said in an email that he agrees juvenile cowbirds are "unlikely to have a mechanism by which they can identify their biological parent from another adult cowbird." But since cowbirds have defined territories, he says it's possible they'll meet their parents again, just by random chance. While some might find this breeding strategy cold, the people who study cowbirds defend them passionately. They're a native species doing what they're meant to do, says Louder, and they're no more cruel than hawks and other birds of prey who snatch up other birds or eggs to eat. Except in rare circumstances where cowbirds heavily outnumber an endangered species, he says, they don't pose population-level threats to other birds.
