You think Honey has a big job!

Have a look at this tweet sent by reader Michael, which he calls “duck adoption agency”:

This of course raises many questions. Why do the mothers do this? (It is of course maladaptive to take care of ducklings who don’t carry your genes.) Is it just that they can’t avoid it when an orphan duckling joins their own brood? Can they distinguish between their own chicks and unrelated ones? Does their inability to do this make them prey to having such large broods?

I’ve written a bird expert about this bizarre phenomenon, so stay tuned.  Perhaps birders have already studied this, but I don’t know from mergansers!

UPDATE: Here is a “Supermom” goldeneye studied by reader Bruce Lyon, whose brood included offspring from six different moms. I’ll let him describe it in the comments. This is only a small part of her brood!

39 Comments

  1. Colin Campbell
    Posted July 9, 2018 at 10:00 am | Permalink

    Mergangsters?

  2. Claudia Baker
    Posted July 9, 2018 at 10:02 am | Permalink

    I haven’t studied mergansers, but I do see this phenomenon every year at the lake where I live in Ontario. The most chicks I have counted at one time is about 30. Sometimes there are two female adults swimming with them, sometimes only one. I have heard that mergansers “babysit” one another’s chicks so that they get a break, but this is only anecdotal.

  3. Pierluigi Ballabeni
    Posted July 9, 2018 at 10:03 am | Permalink

    Maybe the ducklings are relatives of the mother. Does she have to feed them or are they able to get food by themselves? Maybe the costs for the mother are not that important and her fitness increases if she cares for kin ducklings.

    • GBJames
      Posted July 9, 2018 at 10:09 am | Permalink

      My guess is that you are correct, that the cost of looking after a giant collection of ducklings is not that much more than looking after a handful. Either way you paddle around finding good places to eat and scare off the occasional predator. From the chick’s point of view there is also probably a benefit to being in a large group, like schooling fish.

  4. S.K.Graham
    Posted July 9, 2018 at 10:25 am | Permalink

    (1) Pretty sure ducklings feed themselves, so it likely costs the mother very little to have extra chicks following her around.

    (2) Do we know the chicks are completely unrelated? What’s the r-factor? Neighboring broods likely have a decent chance of niece/nephew, 1st/2nd… cousins.

    (3) The largest cost (I imagine) would be in defending them — how actively does the mother defend the extra chicks beyond what is needed to defend her own, if at all? Will she go out of her way to save a straggler that is not her own?

    (4) The other largest cost is food competition. Mother leads her chicks around to where they can find food. If not enough for all, would she drive off the extra chicks? If there is enough for all, then the cost is low or negligible to herself and her own chicks.

    (5) Does the mother keep her own chicks closer? Seems likely. If so, the extra chicks might in some sense act as a buffer between her own & predators.

    (6) If the unrelated ducklings imprint on her, it may be more trouble than it is worth to discourage them from following her around. The benefit to the chicks is likely greater than

    (7) larger group more likely to spot predators early, giving a net benefit to her own chicks.

    It is far from clear that the behavior is a net loss for the mother’s gene’s reproductive success. (5),(6) & (7) combined could possibly be a huge benefit both to the mother & her brood. While the adoptees also benefit.

    • Posted July 9, 2018 at 12:36 pm | Permalink

      Ive seen orphaned ducklings down at the local pond form alliances and fight off much larger ducks who come close to them.

      • S.K.Graham
        Posted July 9, 2018 at 7:14 pm | Permalink

        Interesting, so there could even be simply a strength in numbers advantage for all.

    • Posted July 10, 2018 at 4:44 am | Permalink

      Imprinting happens during a very short period after hatching. If the chicks hatched under a different mother it is not very likely they would then imprint on another one I believe.

  5. CHARLES A SAWICKI
    Posted July 9, 2018 at 10:27 am | Permalink

    Possibly this has a similar survival benefit as is seen for adult birds, bats and fish forming large groups. which seem to confuse predators.

  6. Posted July 9, 2018 at 10:42 am | Permalink

    I’ve noticed that peahens take turns babysitting the young ones. Perhaps the Mergansers do this also.

  7. John Black
    Posted July 9, 2018 at 10:47 am | Permalink

    I don’t know much about wildlife photography or ducks in particular, but I did find it amusing for the tweet to say this was both “an incredible photo” and “not an uncommon sight”. 🙂

    • S.K.Graham
      Posted July 9, 2018 at 11:14 am | Permalink

      Each word is relative to its own context. Within context of seeing mother ducks with broods, not uncommon. Within context of wildlife photos and people’s assumptions/expectations, an incredible shot.

  8. Roger
    Posted July 9, 2018 at 11:33 am | Permalink

    But what of they are shopping and they go to one of those places that only allow two students at a time. They would have to wait like forever.

  9. J Cook
    Posted July 9, 2018 at 11:48 am | Permalink

    Ostriches do that. When I lived in Sudan- Now South Sudan- I saw hen ostriches with 40 and more chicks. It is not a totally benign act with ostriches. It is so common there must be a survival benefit.

    • Jenny Haniver
      Posted July 9, 2018 at 3:53 pm | Permalink

      I learn that the behavior of brooding ostriches is even stranger than that! https://animalcorner.co.uk/animals/ostrich/. According to this info, you must have seen a male ostrich with his communal brood; and sometimes ostriches steal chicks from other broods. The male ostrich cares for the young — Mister Mom.

      Wonder if there’s more to the mergansers and many ducklings than orphaned ducklings being adopted?

      • Jenny Haniver
        Posted July 9, 2018 at 4:43 pm | Permalink

        I’ve found an answer to my question, and it is, Yes, there is more to these supernumerary broods than meets the eye. Apparently, it’s not due to ducklings being orphaned; rather it’s phenomenon called “brood amalgamation,” and this is not unusual in mergansers. It can happen as a parasitic deposit of eggs in another’s nest, communal nests, child stealing, perhaps, and I’m not clear on what else. I’ve found a paper on the subject by John McA. Eadie, et al., “Pre-hatch and post-hatch brood amalgamation among North Americn Anatidae: a review of hypotheses” the link is so long, I doubt that it’ll work, but it’s available on Researchgate. I have not yet given it a thorough read.

  10. Posted July 9, 2018 at 12:05 pm | Permalink

    Franklin gulls do that I think…

  11. Posted July 9, 2018 at 12:18 pm | Permalink

    I remember seeing Canada geese with what I’d guess was an ‘extended family’ previously …

  12. Posted July 9, 2018 at 12:43 pm | Permalink

    I agree. Cost to the mother (or ducklings) to add one more to the brood is low. Benefit of adding itself to the brood is high for an orphan duckling. Having more ducklings around decreases the chance of any one duckling being eaten once the predator has found the brood (though it may slightly increase the chance that the brood is found). Instincts of adult ducks, and presumably young ones, keep them together in flocks most of the year. Driving an unwanted duckling away would be difficult and take time and attention away from the other brood-caring activities the mother could engage in.

    My conclusion. Really big broods look odd to us, but are an inevitable result of selection pressures against rising brood sizes being so low.

  13. George
    Posted July 9, 2018 at 1:11 pm | Permalink

    Jerry needs to give lessons to the Department of the Interior on raising ducks.

    • yazikus
      Posted July 9, 2018 at 1:15 pm | Permalink

      Goodness, is that real??

      • yazikus
        Posted July 9, 2018 at 1:51 pm | Permalink

        It is real. How sad.

        • pck
          Posted July 9, 2018 at 3:06 pm | Permalink

          It’s a Trump appointee, can we really expect them to be capable of taking care of ducks?

  14. loren russell
    Posted July 9, 2018 at 1:14 pm | Permalink

    That poor merganser mom has even more to handle than Miss Anderson did in my 38-pupil combined first and second grade class. (Sumas GS, 1949)

  15. loren russell
    Posted July 9, 2018 at 1:16 pm | Permalink

    Re the Interior Dept duck — Did she re-nest? My understanding is that the chief rat has jumped ship.

  16. Posted July 9, 2018 at 1:46 pm | Permalink

    Some good suggested explanations here.

    Curious – what led to the chicks being orphaned?

    • Posted July 10, 2018 at 4:42 am | Permalink

      They were not necessarily orphaned – see my comment about shelduck above.

  17. David Evans
    Posted July 9, 2018 at 2:33 pm | Permalink

    If I saw this at Loch Ness, at a greater distance, I can imagine getting quite excited. In fact I have never seen a group of more than about 6 ducklings there.

    • GBJames
      Posted July 9, 2018 at 2:47 pm | Permalink

      Most get eaten by Nessie!

      • Posted July 11, 2018 at 11:16 am | Permalink

        And since Nessie is a time-travelling plesiosaur, we’ll never find them!

        (to mix two 1980s tropes.)

  18. Posted July 9, 2018 at 4:03 pm | Permalink

    “(6) If the unrelated ducklings imprint on her, it may be more trouble than it is worth to discourage them from following her around.”

    I’ve only heard of “imprinting” from babies to the mama, or surrogate mama. But, maybe imprinting occurs from same species mamas or surrogate mamas to mamaless babies also. One of the supposed benefits of “cute” defenseless babies is the desire they instill in adults in general. All Trumpites excluded)to care for them until they’re able to care for themselves (sometimes called adulthood).

    Another weird thought is that maybe this is
    just herding instinct on a smaller scale. The benefit to this mama Merganser is extended to the survival of the group.

    Looking forward to answers.

  19. Posted July 9, 2018 at 6:01 pm | Permalink

    Since it is possible that they all be related as in, adults, off spring, nearly always return to the same lake, pond to breed… it could well be kin selection.
    The “tail” end could be picked off by predation but her young are nearest (to defend) which helps increase her fitness, survival rate of her young with little cost.
    All in all it is a amazing and interesting sight.

    • Posted July 10, 2018 at 4:46 am | Permalink

      Assuming that her own chicks are the ones nearest to her of course. I don’t know what evidence there is for that.

  20. Robert Bate
    Posted July 10, 2018 at 5:52 am | Permalink

    Interesting Common Merganser side note. I recently saw a Common Loon stalking a brood of Common Mergansers in Maine. The loon maintains a low profile in the water and eases close to the hen and brood. The mother merganser was very agitated and shepherded the chicks into safe harbor is shallow water under a dock walkway. Loons must have a taste for merganser chicks.

  21. Bruce Lyon
    Posted July 10, 2018 at 12:00 pm | Permalink

    Jerry asked me to provide some information because I have worked on adoption in waterfowl. I don’t know what goes on in mergansers but I did a study of adoption with John Eadie in Barrow’s Goldeneneyes in British Columbia (American Naturalist 1998; Eadie is now at UC Davis). Eadie wrote the foundational paper on adoption in waterfowl, which one of the readers found and commented on above. Eadie then did his thesis work on goldeneyes to test some of these ideas in the review paper. In goldeneyes, there are two ways that females end up raising ducklings of other females—brood parasitism, where a female lays eggs in the nest of another female, and adoption after hatching.

    Goldeneye ducks are great for studying adoption because a given lake often has only several females. The ducklings have nice white cheek patches which can be marked with colored permanent markers. Each nesting female gets her own brood color (same cheek same color for whole brood; e.g. blue left cheek). When ducklings are adopted it is then possible to know which brood (and mom) the duckling originally came from. Jerry posted a photo of Supermom with part of her brood and you can see the different cheek colors. Her own chicks were unmarked and the photo shows three different colors on the left cheeks (yellow, green and blue). Some of the other chicks were marked on their right chicks so you cannot see their colors in photo. Supermom adopted chicks from five different females and she had something like 30 ducklings. Her brood was colorful like a Christmas tree. Mom has her own colors — a plastic nasal saddle that allows us to identify individual adults (color bands on feet would be useless for trying to ID females swimming out in a lake)

    At least a couple of different explanations might account for the adoption in waterfowl: there is safety in numbers so females are happy to adopt kids from other broods or adoption is a form of post-hatching brood parasitism where the biological mother of the adopted ducklings benefits by fobbing her chicks off on someone else. Depending on whether adoption is costly for the foster mom, she might be neutral or against it. If chick recognition is not possible, there might also be nothing she can do about it. In Canada Geese, there are studies of kidnapping of young—apparently having additional goslings is so good that the adults appear to kidnap each other’s chicks. At least that is what is claimed.

    For goldeneye, my colleague Eadie was pretty sure at the start of the study that adoption is beneficial to all. However, we did brood size manipulations and found that there was no cost or benefit to adoption. The females that gave up their ducklings were females with smaller than average broods—we argued that these small brood would yield small payoffs for the females, that the costs of staying exceeded the benefits given that they could find a foster mom. For goldeneyes it seems that the brood desertion maybe what drives adoption. These females seemed to take their brood over to another female, who would fight with the intruder and chase her off. The ducklings then insinuate themselves into the brood and, voila, adoption is achieved.

    As to whether foster moms can distinguish their own ducklings from the foreign ducklings, we did some duckling addition experiments to see if moms would happily adopt kids and the will as long as the introduced ducklings were the same age as their own. When we tried to introduce smaller ducklings into broods of older ducklings the moms would invariably attack the ducklings and try to kill them (we rescued all of these experimental ducklings and got them safely into broods of the same age). This is where John Eadie’s jaw dropped—he thought that foster moms would welcome additional ducklings but this was not always the case. We joke about a spit of land we called Epiphany Point—it is where we watched the first attempted infanticide and it fundamentally altered John’s thinking about adoption.

    • GBJames
      Posted July 10, 2018 at 12:31 pm | Permalink

      Very interesting. Thanks, Bruce!


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