Incest can lead to more disease in offspring, crow study finds - Phys.org

Wren: Welcome back to Bird Brains — the show where "bird brain" is absolutely, unequivocally a compliment. I'm Wren, ornithologist, corvid obsessive, and your guide to the surprisingly rich inner lives of crows, ravens, magpies, and jays. Today we've got tool-using species that nobody saw coming, the science of why a crow might remember your face for years — and hold a grudge about it — and a study about crow family life that turns out to be more relatable than you'd expect. Before we dive in, a big thank you to today's sponsors: Ada, who help businesses integrate A I into their workflows in smart, practical ways; Ago Consulting — that's "Ahh-Go" Consulting — silicon development experts working across everything from A I to SoC; and Zen Semiconductor, an umbrella company with a whole portfolio of businesses across the silicon industry. These three are the reason this show exists, and I'm genuinely grateful. Alright — let's get into it. Wren: So, I want to start with something that genuinely made me do a double-take when I saw it land in my research feed this week. A new paper published in Ecology and Evolution — a peer-reviewed journal from Wiley — documented opportunistic tool use in two corvid species that researchers weren't really expecting to see it in. Now, when most people think about corvid tool use, they go straight to New Caledonian crows. And fair enough — those birds are essentially the poster children for avian intelligence. They craft hooks out of plant stems, they'll carry a tool from one location to another because they know they'll need it later. That's not instinct, that is planning. But the exciting thing about this new study is that it widens the lens. The researchers — Giri and colleagues, publishing in 2025 — observed corvid species engaging with tools opportunistically, meaning not as a deeply ingrained, species-wide habit, but as a flexible, in-the-moment response to a problem. And that distinction matters enormously. Wren: Here's why it matters. When a behavior is rigid and instinctive, it doesn't tell us much about cognition. But when an animal sees a situation, assesses it, picks up an object, and uses it to solve a problem it's never encountered in exactly that form before — that's insight. That's flexibility. That's the hallmark of a genuinely intelligent mind. And what the corvid family keeps showing us, study after study, is that this flexibility isn't confined to a couple of famous species. It seems to be something the whole family has some capacity for, even if it shows up more strongly in some than others. The researchers described the behavior as opportunistic — the birds weren't trained, they weren't in a highly controlled lab setting designed to elicit tool use. They just... did it. Which, honestly? Is more impressive. A lab result tells you an animal can do something under optimal conditions. A field observation tells you they actually do it in their real lives. Wren: And this fits into a broader picture that corvid researchers have been building for decades. These birds have relatively large brains for their body size — comparable, in terms of brain-to-body ratio, to great apes. Their forebrains, the regions associated with complex cognition, are proportionally massive. And crucially, they have long childhoods by bird standards. Young crows and ravens spend extended time with their parents, learning, watching, and experimenting. That's a recipe for cultural transmission — for knowledge to pass from generation to generation, not through genes, but through behavior. So when we see a new species picking up a tool, we're not just seeing one clever individual. We're potentially seeing the edge of something much bigger — a capacity that's been quietly sitting in the corvid family tree all along, waiting for the right moment to show itself. Wren: Alright, let's shift gears and talk about something that genuinely sits at the intersection of cool science and mild personal terror — and I mean that lovingly. Let's talk about how crows recognize human faces. Because they do. They absolutely do. And the research on this is robust, well-replicated, and frankly a little humbling. The most cited work here comes out of the University of Washington, where researcher John Marzluff and his colleagues ran a now-famous series of experiments involving — and I love this detail — caveman masks. The researchers would wear a specific mask while trapping and banding crows, which the crows quite reasonably found distressing. Then, weeks and months later, anyone wearing that same mask on campus would get scolded. Dive-bombed. Followed. The crows remembered the face — well, the mask — associated it with danger, and held onto that information. Wren: But here's where it gets really interesting. The crows didn't just remember individually. They taught other crows. Birds who had never been trapped, who had never seen the original capture event, learned to scold the dangerous mask — presumably because they observed other crows doing it, or because they were warned somehow through corvid social signaling. The knowledge spread through the population. That is culture. That is the social transmission of learned information, which is something we used to think was pretty much exclusive to humans and a handful of other mammals. And crows are doing it from a brain roughly the size of a walnut. I don't say that to be dismissive — I say it because it is staggering. The efficiency of that little brain is off the charts. Wren: Now, the face recognition itself — how does it work? Research suggests crows are processing faces holistically, much like humans do. We don't recognize people by cataloguing individual features — that's the nose, that's the eyebrow — we recognize the whole face as a unified pattern. Crows appear to do something similar. They can distinguish between individual human faces with remarkable accuracy, and they maintain those distinctions over years. Years. There are accounts in the research literature of crows holding grudges for over five years. Think about that the next time you're tempted to shoo one away from your bin. You may be making a very long-term enemy. And the flip side of that, which I think is just as important, is that crows also remember kindness. If you consistently leave food for a crow, if you treat it well, it will remember you as safe, as friendly. Some people have built genuine, long-term relationships with individual crows this way — and there's documented evidence of crows bringing gifts to humans they've bonded with. Shiny objects, buttons, bits of interesting debris. It sounds like a fairytale but it is a documented, real thing. Wren: So what is actually happening in that brain? Corvid neuroscience has come a long way in the last twenty years, and what researchers have found is that the crow brain, while structured differently from a mammalian brain, achieves similar computational results through a different architecture. Mammals have a layered cortex. Birds don't — their equivalent regions are organized differently, in clusters rather than layers. For a long time, this was interpreted as evidence of lower intelligence. We now know that was wrong. The clustering can be just as effective for complex processing. Crows have a region called the nidopallium caudolaterale which functions analogously to the prefrontal cortex in mammals — the part of our brain associated with planning, decision-making, and working memory. When crows are solving problems, this region lights up. It's doing the same job through a different design. Nature, it turns out, found intelligence twice — or maybe more than twice — through very different paths. Wren: Now I want to spend some time on a story that caught my attention for slightly different reasons — because it's not just about how smart crows are, it's about what that intelligence costs them, and what it tells us about the pressures shaping their lives. A study reported by Phys.org looked at inbreeding in crows — specifically, at how inbreeding affects offspring health. And the findings were fairly striking: crow offspring born from related parents showed higher rates of disease. Now, inbreeding depression — the technical term for this — is well-documented across many species. It's not unique to crows. But what makes this interesting in the context of corvid intelligence is what it implies about crow social structure and mate choice. Wren: Crows are not random in who they pair with. They have complex social lives, they recognize individuals, they maintain long-term social bonds. In many corvid species, pairs mate for life — or at least for many years. Young crows often stay in their natal territory for a while, helping to raise younger siblings, before eventually dispersing. This extended family structure creates both opportunities and risks. The opportunity is that knowledge and skills can be passed down through close social groups. The risk is that in small or isolated populations, you end up with individuals who are related mating with each other, and the health consequences can be significant. Wren: What I find fascinating here is the evolutionary tension at play. The very social structures that make crows so smart — the long family bonds, the extended learning period, the tight-knit communities — are the same structures that create the conditions for inbreeding in fragmented habitats. And habitat fragmentation is a very real and growing problem. As we develop land, as we break up continuous habitat into isolated patches, we force animal populations into smaller and smaller islands. For a species like the crow, which depends on rich social networks and multigenerational learning, the consequences of that fragmentation go beyond just losing individuals. You risk losing the cultural knowledge those individuals carry. You risk the genetic health of the group. It's a reminder that protecting wildlife isn't just about counting individuals — it's about preserving the conditions that allow their intelligence and their cultures to thrive. Wren: There's also something quietly poignant about this research. Crows can recognize faces. They remember individuals. They form bonds. And when those bonds happen to be between relatives who then produce offspring together, the costs are real and measurable. These are animals with enough social complexity that the human concepts of family, loyalty, and community actually apply in some meaningful sense. Which makes the health consequences of isolation feel a little less like dry genetics and a little more like a story about what happens when a community gets cut off from the wider world. Wren: And you know, that's the thing I keep coming back to when I read piece after piece asking "are crows really that clever?" — because yes, that question is genuinely being asked and debated in the scientific literature, and it's a fair question. Science should always push back, demand replication, check for alternative explanations. Good corvid research does that. The University of Washington face recognition work has been replicated. The New Caledonian crow tool use has been studied from dozens of angles. The cache protection behaviors — where scrub jays will move their hidden food if they notice another jay watching them — have been tested rigorously. These are not flukes. The skeptical questions are worth asking, and the evidence keeps holding up. Crows really are that clever. The debate, at this point, is mostly about the mechanisms and the degree, not the basic fact. Wren: What I think is important, though, is to resist the temptation to only celebrate corvid intelligence when it looks like a human solving a puzzle. The food-caching behavior of a Clark's nutcracker — which can hide up to thirty thousand pine seeds across hundreds of locations and remember where most of them are nine months later — is not the same kind of intelligence as a crow using a tool, but it is extraordinary in its own right. Spatial memory of that precision is a genuinely mind-bending cognitive feat. The problem-solving of a raven figuring out how to reach meat hanging from a string by pulling it up in loops with its foot and standing on the loops — that's insight. The way a magpie passes the mirror test — recognizing its own reflection, understanding that the mark on its body is on itself and not some other bird — that's self-awareness, or something functionally very close to it. These are different flavors of intelligence, and they're all real, and they're all worth celebrating. Wren: I want to close out with a story that I think captures something essential about why corvids matter — not just as scientific subjects, but as neighbors. Because that's what they are. Crows and ravens and magpies and jays are not wilderness animals that humans occasionally glimpse. They are urban, suburban, and rural generalists who have chosen — and I use that word deliberately — to live alongside us. They have adapted to our cities, learned our schedules, exploited our waste, and in doing so, become some of the most closely observed wild animals on the planet. Wren: There's a well-documented case that became famous through the work of wildlife researcher Gabi Mann in Seattle, who as a child started regularly feeding a group of crows. And the crows, over time, started bringing her gifts. Buttons, pieces of foam, a small pearl-colored heart, a piece of metal with the word "best" on it. Researchers who have studied this behavior suggest it's a form of reciprocal exchange — the crows understood, on some level, that she was giving them something, and they gave back. Not because they were trained to. Not because there was a reward. Because they are social animals who engage in reciprocal relationships, and she had become part of their social world. Wren: I find that story almost unbearably wonderful. Here is a child, feeding birds in her backyard, and the birds — with their walnut-sized brains and their sharp black eyes — are paying enough attention to notice her kindness, remember her face, track her over time, and decide to give her something back. That is not instinct. That is not conditioning in any simple sense. That is a relationship. And it's one that formed across what we might have once called an unbridgeable cognitive divide — between a human child and a crow — but which turns out to be not nearly as wide as we thought. Wren: Urban crows in particular have become extraordinarily good at reading human behavior. They know the difference between a person who is paying attention to them and one who isn't. They know when a researcher is watching versus when they're not, and some studies have shown they modify their caching behavior accordingly — hiding food in ways that are harder to observe when they think they're being watched. They use traffic patterns — placing nuts in front of cars to crack them open, and timing their retrieval to traffic lights. They understand cause and effect in the human world and they exploit it with casual brilliance. They are, in the truest sense, paying attention to us. The question is whether we're paying attention back. Wren: And I think that's what this show is really about. Not just the science — though the science is wonderful — but the invitation to pay attention. To look up when a crow is watching you and wonder what it's thinking. To recognize that intelligence is not our exclusive possession, that it evolved multiple times in multiple forms, and that some of its most vivid expressions are living in the trees outside your window right now, watching you walk to your car, remembering your face, and possibly, if you've been kind, planning a small strange gift. Wren: Intelligence lives in unexpected places. That's the lesson corvids keep teaching us, study after study, year after year. The more carefully we look, the more we find minds where we didn't expect them — problem-solving, remembering, teaching, grieving, playing, and yes, occasionally holding a very long and very justified grudge. Bird Brains, brought to you by Ada, Ago Consulting, and Zen Semiconductor — three teams who, come to think of it, know a thing or two about building intelligence in unexpected forms. If today's episode surprised you, delighted you, or made you slightly nervous about the crow on your fence, please subscribe, leave a review, and share it with someone who thinks "bird brain" is still an insult. We're going to change their mind. Show notes with links to all the research we talked about today are right there waiting for you — the link in show notes. Stay curious. I'll see you next time.