Readers’ wildlife photos (with more science)

We have another great installment in Professor Bruce Lyon‘s series of researches on the biology and behavioral evolution of American coots (Fulica americana). He added this in his email: “This one is a bit different since it focuses on one very specific study and quite a bit on a former student of mine but I think your readers might enjoy a behind-the-scenes view of how science is often done. Lay people often have a Hollywood view of how science is done (antisocial nerds in lab coats, everything turning out just as the complex math on the blackboard” predicts).

Bruce’s notes are indented.

Another installment about our work with American coots (previous posts herehereherehere). Today I focus on an amazing discovery made by my former PhD student Dai Shizuka (now a professor in Nebraska). In my PhD thesis work, I concluded that American coots do not recognize brood parasitic chicks. With a combination of key natural history insights and elegant experiments, Dai proved me wrong and I was delighted about the outcome. This research was the single most exciting project I have ever been involved with.

The story has a few messages that may interest readers—the discoveries themselves, but also the important realization that science is often a messy meandering path to enlightenment. Experiments often fail, but sometimes in ways that yield important new insights. In addition, incidental natural history observations that initially seem weird and puzzling can turn out to be vitally important for figuring out what is going on. And a bonus coincidence: Dai Shizuku was a postdoc with Jerry’s colleague Trevor Price at Chicago and was based in the lab right next door to Jerry for a year.

Below: Dai Shizuka at our BC site.

Below: My initial conclusion that coots don’t recognize parasitic chicks was not surprising given what we know about the more famous interspecific brood parasites like cuckoos and cowbirds. Virtually all of their hosts fail to recognize parasitic chicks, even when the difference between host and parasite is ridiculous, as the photo below of a common cuckoo (Cuculus canoris) and Eurasian reed warbler (Acrocephalus scirpaceusshows. The cuckoo chick looks nothing like the host and is several times larger than its foster parents (photo from the web). This lack of chick recognition has long been an evolutionary puzzle, particularly because the hosts are often extremely good at recognizing cuckoo eggs that differ only subtly from their own eggs.

Below: Back to within species parasitism in coots: can you spot the parasites? I bet you can’t because I would not be able to do so without notes on which chicks came from which eggs. This is an experimental brood that contains some chicks that are not the host’s own chicks (I know this because we added them to the brood).

Dai did not set out to study chick recognition; this would have been a crazy idea for a PhD project given the lack of recognition in systems like cuckoo hosts. Instead, he was interested in the function of the extreme hatching asynchrony coots show and he set up some exploratory experiments in which he created synchronously hatching broods by swapping chicks between nests.

Below: We hatch all of the coot chicks in incubators at the field cabin, which makes it easy to swap chicks among broods for experiments. We collect eggs from their nest as soon as they show signs of hatching (slight cracks on the shell) and return the hatched chicks to a nest (home or foster nest depending on the experiment) on the day they hatch. Due to the hatching asynchrony, we have to visit the same nest several days in a row to get all of the hatching eggs and releasing chicks back to the nest. The photo below shows Dai processing chicks in our three incubators.

Swapping offspring among families (called cross fostering) has a long history in evolutionary biology; it is used in heritability studies to control for environmental affects on traits. A critically important assumption is that foster parents treat the cross-fostered offspring as they would their own, but of course coots have a mind of their own. Dai came to me one day with both bad and good news. The bad news: the cross fostering experiments failed as a method to investigate hatch patterns because the fostered chicks had significantly worse survival than the host’s own chicks. The good news: this survival pattern suggested that coots might be able to recognize some parasitic chicks. Cross fostering is like adding parasitic chicks to a brood; the birds are given chicks of another pair, and when these chicks do worse it would most likely be due to discrimination by the foster parents. These preliminary results called for a full-scale experimental study to investigate chick recognition!

The following year we repeated the same experiment but with a much larger sample size. After a hell of a lot of work, we found no evidence for recognition. The year after that, more experiments and more toiling, but again not a shred of evidence for recognition. We even did a second experiment that involved cross fostering chicks while maintaining the normal pattern of hatching asynchrony, but this too failed to show evidence for recognition.

Now, a sane person would have given up at this point and concluded that the birds really don’t recognize parasitic chicks. However, Mother Nature kept teasing us with tantalizing signs that these birds really can distinguish their own chicks from brood parasites. While conducting brood observations from a floating blind, both parents of a brood I was observing suddenly turned on one of their chicks and began to peck at it really aggressively in a way that differed from normal spankings. There were several bouts of these attacks and it seemed they occurred whenever the chick called out. I eventually lost track of the chick, but Dai found it dead in the marsh a few hours later. Its tag revealed something really interesting—the chick was from a brood parasitic egg! This was the first time we had witnessed direct infanticide and it involved a brood parasite. The video below shows this attack:

Second, adoption is very rare in our population, so it was bizarre when a coot pair adopted three chicks from their neighbor. Checking the chick ID’s in our records revealed that all three adoptees were from parasitic eggs the adopting female had laid in the neighbor’s nest. The parasitic chicks had come back home to their biological parents! If this story involved humans, Hollywood would be asking for a movie script about now. This observation suggested that the parents recognized the chicks as their biological kids even though they had hatched in the neighbor’s nest.

These intriguing natural history observations suggested that we were missing something with our experiments. The critical missing piece came from an observation of what appeared to be a completely deranged pair of coots. Once again I was in a floating blind observing a pair of coots with their very recently hatched chicks. Everything seemed to be normal but then a switch seemed to go off—one of the parents started to kill its own chicks, one by one, until they had all been killed off. I was stunned because we had never seen anything like this before and we were also certain that these were the biological chicks of these parents.  Here is a video showing the chick killing behavior (a different brood from experiments described below but it shows exactly the behavior I saw with the killer parents):

Several days later, over dinner, Dai made sense of why these birds went crazy, and he had an epiphany that solved everything. During dinner discussions, one of the field assistants recalled seeing the crazy killer parent coots feeding two chicks for a short period of time before their own eggs hatched. These birds had temporarily adopted their neighbors’ chicks before their own eggs had hatched, but the chicks returned home before the pair’s own eggs hatched. Dai reasoned that coots learn to recognize their chicks and that the short exposure to the wrong kids had caused these parents to learn from the wrong chicks and then when their own chicks hatched, to incorrectly see their own chicks as brood parasites.

This line of thinking led to the hypothesis that coots learn to recognize their chicks by imprinting on the chicks that hatch on the first day—they use these first hatched chicks as reference chicks to learn some recognition feature that they could then apply to chicks that hatch on the following days. The simple rule of using chicks that hatch on the first hatching day would be a pretty reliable rule since at most nests, only host chicks hatch on the first hatching day. The chicks’ features that the parents learn could involve vocalizations, smell or visual appearance—or a combination of these. To be useful, the features would have to vary among pairs but not within a pair’s own brood—just like the way they recognize eggs. This hypothesis could also explain our consistent failures up to that point. If parents learn from the chicks that hatch on the first day, then parents at nests where both hosts and parasites hatch on the first day would learn that both chick types are their own and would not be able to recognize parasite chicks. This was the design of all of previous experiments. Doh!

These insights came near the end of what was supposed to be the final field season of the project, but we decided that the idea was so interesting that it needed to be tested. So we went back one final year—it was do or die for showing that coots recognize parasitic chicks.

We conducted two main experiments to test Dai’s hypothesis. Since we hatch all chicks in captivity, we got to decide which chicks parents are exposed to, and in what order. In the ‘host first’ experiment, we gave birds their own chicks on the first hatch day, and then gave an equal mix of host and foreign chick on each day after that. Foreign chicks were chicks from a second brood and are the equivalent of brood parasites. The graphic below shows the experimental design. If parents use the day 1 chicks to learn which chicks are their own, then we can predict that the foreign (‘parasite’) chicks will survive less well than the host chicks (assessed only for chicks from days when both types hatch). For testing mechanisms like learning, real proof comes from tricking the birds to do the wrong thing. We therefore did a second experiment where birds were given only foreign chicks on day 1 and then an equal mix of host and foreign on later days (‘foreign first’ experiment). If the birds really do learn from the first hatched chicks then they should imprint on wrong chicks and discriminate against their own chicks.

After setting up the first few experiments, we were on pins and needles. Then, after surveying only three broods I knew that we had finally broken the curse. The results were so clear and strong that we now had convincing experimental evidence that coots can recognize parasitic chicks. Birds given their own chicks on the first day were able to recognize many of the parasitic chicks that hatched from day 2 onward, while birds given somebody else’s chicks on the first day treated their own chicks as parasitic. Evidence for recognition came from big survival differences between chick types that matched predictions. And these survival differences happened so quickly that we were barely able to see what exactly was causing them (the differences had already happened before our first survey on most broods). However, we were able to watch a few broods right at hatching to see what was happening. Just like the deranged pair of coots that killed all of their own kids, these birds very quickly dispatched many of the chicks that were the ‘wrong’ chicks. In three broods we only saw the female culling the chicks but in another brood both sexes were involved. Our experiment not only showed chick recognition, but how it occurs: parents learn something about the chicks that hatch on the first day. We do not yet know what information the parents learn but I strongly suspect that the information is in the chicks’ vocalizations.

We are aware that experiments like ours do raise some ethical considerations. However, keep in mind that we did not create unnatural behaviors that do not normally exist. Moreover, at our site each year thousands of coot chicks die naturally from starvation; it is not clear to me that this is a kinder fate than what happens to the brood parasite chicks.

32 Comments

  1. ThyroidPlanet
    Posted August 20, 2017 at 9:03 am | Permalink

    Sub

  2. Posted August 20, 2017 at 9:30 am | Permalink

    This lack of chick recognition has long been an evolutionary puzzle….

    Didn’t Tinbergen show that only one or two stimuli are required to elicit feeding behavior in chicks and parents?

    … a coot pair adopted three chicks from their neighbor.… all three adoptees were from parasitic eggs the adopting female had laid in the neighbor’s nest. The parasitic chicks had come back home to their biological parents! This observation suggested that the parents recognized the chicks as their biological kids even though they had hatched in the neighbor’s nest.

    Would these reunions perhaps be an integral part of the strategy?

    • Randy schenck
      Posted August 20, 2017 at 9:47 am | Permalink

      That is a very interesting question. Also need to know, were these three chicks who returned to their biological parents the first chicks for them?? Had they already had parasitic chicks, maybe this reunion would not be happening.

      • Bruce Lyon
        Posted August 20, 2017 at 3:20 pm | Permalink

        Excellent question. If I recall correctly, o these chicks were not the first chicks for these parents. This would not have mattered because the first chicks of the adopting parents were also their own chicks. In case it was not clear, the parents will accept any chicks that are the same ‘type’ as their first hatched chicks. If those chicks were the birds own chicks then they will happily accept other chicks that are also their own chicks.

    • Bruce Lyon
      Posted August 20, 2017 at 3:18 pm | Permalink

      I suspect that the cues or signals that coots use to decide which chicks to feed are likely to be different from those that allow parents to recognize or cull chicks. Probably two levels of decisions: should I keep the chick and if I keep it, how much should I feed it.

      In term of adoption of own kids laid in somebody else’s nest I also suspect that this is unlikely to be a key part of the strategy, mostly because our data suggest that the reason the parents lay the eggs in a neighbor’s nest in the first place, and not their own, is because they can lay more eggs that they can provide food for.

      • Posted August 21, 2017 at 1:48 am | Permalink

        That all makes sense.

  3. gravelinspector-Aidan
    Posted August 20, 2017 at 9:47 am | Permalink

    Checking the chick ID’s in our records revealed that all three adoptees were from parasitic eggs the adopting female had laid in the neighbor’s nest. The parasitic chicks had come back home to their biological parents! If this story involved humans, Hollywood would be asking for a movie script about now.

    Disney wouldn’t. Too … “non-nuclear 2.4 children and Spot the dog”.

  4. Heather Hastie
    Posted August 20, 2017 at 9:55 am | Permalink

    Fascinating stuff!

    You say that at your site lots of chicks die via starvation. I wonder how or whether it would affect results if there was plenty of food for all chicks.

    I think it’s possible that other birds (like those feeding cuckoo chicks etc) can tell the difference when the difference in appearance is so obvious, but feed the interlopers anyway because of a natural urge to parent. We see inter-species behaviour like that all the time in controlled environments where humans are ensuring a plentiful food supply. I’d be interested to know if food supply has an influence.

    • Bruce Lyon
      Posted August 20, 2017 at 3:32 pm | Permalink

      Great question. I suspect if there was lots of food it would cost little to raise parasitic chicks and the birds would then neither reject eggs or chicks.

      In terms of cuckoos, I am not convinced that an urge is a sufficient explanation because the result (feeding a cuckoo) comes with a big cost. Also, there is lots of evidence that birds in general are pretty good at not making dopey choices about who to feed. For example in lots of seabirds that nest in colonies chick recognition is very well developed and despite an abundance of chicks that try to get food from birds that are not their own parents, the parents are good at finding their own kids. The examples of birds that feed the wrong species are often unusual cases where birds lose their own kids but still have the urge to feed something, like the famous cardinal that fed a goldfish.

      • Heather Hastie
        Posted August 20, 2017 at 6:11 pm | Permalink

        Thanks. 🙂

  5. Posted August 20, 2017 at 11:20 am | Permalink

    Fascinating work.

    • Michael Fisher
      Posted August 20, 2017 at 12:56 pm | Permalink

      @Katiness Everdeen Yes, it’s entirely possible – there are many pictures like that Twitter pic on Google images, just search for: end of a rainbow.

      However the location where the rainbow ‘appears’ to meet the ground is observer dependent. Move to the left, right, forward, backward & the ‘bow moves too. If the ground entirely disappeared you would see a circular rainbow. Somebody across the road looking back at the van & the photographer would see the sun low in the sky & no rainbow at all.

  6. rickflick
    Posted August 20, 2017 at 11:52 am | Permalink

    I can see that a lot of work and determination went into this project – rewarded by some surprising results. I bet there is a great satisfaction in having hung in there.

  7. Charles Sawicki
    Posted August 20, 2017 at 12:06 pm | Permalink

    Nice work! Experimental research often involves many false starts and dogged determination.

  8. Michael Fisher
    Posted August 20, 2017 at 12:58 pm | Permalink

    Very lovely experiment!

    What is the role of Bounce in these experiments [the first pic]? Are coot chicks a bit ‘clingy’ from fluffy feathered static? 🙂

    • Bruce Lyon
      Posted August 20, 2017 at 3:26 pm | Permalink

      Your comment made me giggle! The answer is very boring: the best place for the incubators was the laundry room. Bounce just happened to be nearby.

      • rickflick
        Posted August 20, 2017 at 7:26 pm | Permalink

        Ken Ham might think Bounce was a secret ingredient used by scientists to tweak their results. 😉

  9. Paul S
    Posted August 20, 2017 at 1:34 pm | Permalink

    Fascinating research, answered my question about chick recognition from your previous post.

  10. Mark R.
    Posted August 20, 2017 at 3:06 pm | Permalink

    Thanks for sharing these interesting scientific discoveries. It was a fascinating mystery and not at all “elementary”.

    You say thousands of coot chicks die every year. Is this common for other birds or are coots a stand-out in this regard?

    • Bruce Lyon
      Posted August 20, 2017 at 3:24 pm | Permalink

      As far as I can tell coots are standouts. I think this is because their eggs are so cheap that they can afford to hedge their bets a lot (lay a super optimistic clutch size for the best possible situation) and then cull when reality sets in. Reality is often a lot worse than the very best possibility, hence lots of starvation.

      • Mark R.
        Posted August 20, 2017 at 6:41 pm | Permalink

        I see; thanks for the info Bruce.

  11. Posted August 20, 2017 at 3:23 pm | Permalink

    Wow, fascinating experiments!

    Regarding the ethics addendum in the last paragraph, is there some kind of ethical approval you needed to get to perform these experiments? I work pretty much exclusively with passively generated data, so I’ve never had to wrestle with ethics boards or the like. Are their ethical approval steps at your university and the province, or just the university?

    • Bruce Lyon
      Posted August 20, 2017 at 4:42 pm | Permalink

      Yes, there are now several approvals. Most important is the Animal Care committees at universities. These can be pretty tough at times. There are also various government agencies that provide banding or research permits and these agencies also make sure that ethical concerns are being met. And then at the publishing stage, many journals also have ethical guidelines that can prevent publication. I am certain that had we proposed the work with a bird that normally does not have lots of naturally induced parental driven mortality of chicks that we would have been denied permits and I think that would be the right call. For most of our work, the effect we are having it not to increase chick mortality but to play ‘god’ (or worse, scientist!) and decide which chicks get to live and which get to die.

      • Posted August 20, 2017 at 11:18 pm | Permalink

        Thanks for the info – super interesting!

  12. Posted August 20, 2017 at 4:32 pm | Permalink

    It is tough being a coots chick. A tragedy of errors for some as it seems imprinting (that was super interesting) can be very dangerous to the innocent in the wild, like indoctrination can be to humans. Sorry, can’t help myself.
    I thoroughly enjoyed this instalment and the work of the team Prof Lyon. Thanks for the post.

  13. Barbara Radcliffe
    Posted August 20, 2017 at 6:11 pm | Permalink

    Thank you for the fascinating story, and congratulations to both you and Dai Shizuoka for your insight and perseverance.
    You mentioned in a reply to my previous comment that you are aware of the work on superb fairy wrens in the Australian National Botanic Garden.
    I wonder if you would be kind enough to advise me of the reference to the publication(s)? I’d like to chase them down and read them properly.
    Thank you.

    • Bruce Lyon
      Posted August 20, 2017 at 7:27 pm | Permalink

      Probably easiest if you just send me an email and I can reply and send you the pdfs. belyon@ucsc.edu

  14. rickflick
    Posted August 20, 2017 at 7:24 pm | Permalink

    I wonder, Bruce, if you think there is pressure for chicks to disguise their vocalizations to match the nestlings? So we’d have an increase in the success of parasitism.

    I’m wondering too if there might be a tendency of parents to distinguish not just the initial chicks they see, but rather those of their own genotype, via vocal or other means? Might these forces change the dynamic in future generations? Or would it take a million years to find out?

    • Bruce Lyon
      Posted August 20, 2017 at 10:07 pm | Permalink

      To be clear, note that we have no real evidence that it is actually vocalizations. This is just an educated hunch. However, assuming that it is vocalizations, what you suggest would require that chicks learn vocalizations. A large amount of evidence suggests that such learning is possible only in three groups of birds: parrots, hummingbirds and songbirds.

      For your second point, I think that what you are suggesting is innate (instinct) recognition, which is the opposite of what we showed. It is possible that there is some innate recognition above and beyond the learning we showed but since the learning patterns are quite strong the innate aspects would have to be fairly minor.

      • rickflick
        Posted August 20, 2017 at 10:23 pm | Permalink

        I see your point(s). Thanks.

  15. Diane G.
    Posted August 22, 2017 at 12:56 am | Permalink

    Great story! (Once again. I hope there’s more in the pipeline! 🙂 )


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