Latest / Ducks Unlimited Podcast / Ep. 580 – Can Ducks Drink Salt Water?
Transcript
- Mike Brasher: Hey everyone, welcome back. I am Dr. Mike Brasher. I'm going to be your host on this episode and we are joined today by a return guest all the way from Canada, Dr. Sarah Gutowsky, a quantitative wildlife ecologist with Environment and Climate Change Canada. Sarah, great to have you back with us again. Thanks for having me. And so for those that missed you the previous episode you were on, give us a real quick snapshot of who you are and what you do now. Dr. Sarah Gutowsky: Sure. Yeah. So I'm a, like you said, a quantitative biologist and my focus mostly on seabirds and sea ducks. I work with the Canadian Wildlife Service branch of ECCC and I'm in a unit where we work on wildlife monitoring and assessment. So my job is sort of to try to get a handle on, you know, how many birds we've got in the seabird and sea duck realm and how they're doing. Mike Brasher: One of the things that we talked at length about on the previous episode was your experience as a expedition guide. And so if folks missed that episode, I strongly encourage you to go back and find that and listen to it. It was a fascinating discussion and I think made a lot of people envious of the experiences that you've had traveling to faraway places and seeing amazing things. That experience and the expertise that you've developed through some of your studies and some of your research has positioned you well for the discussion that we're going to have today. We originally hoped to discuss this topic sort of as a bonus discussion in that episode, but we got kind of carried away and went for longer than what we thought we would, which is not uncommon. But this, we're going to talk about, just sort of generally stated, birds' ability to tolerate saltwater and some of the different adaptations that make that possible for them. And this question came to me, I guess, last fall by a friend that I have down in Louisiana. Last year was a time of exceptional drought in the southern U.S. and a lot of the coastal marshes that typically carry water to some degree throughout the year were completely dry, like cracked marsh, cracked ground. and water not even in some of the canals that dissect a lot of that landscape. And so, the question came to me like, well, what are ducks going to do in this situation? Where are they going to get water that they need to sustain life? Are they able to drink salt water? And so, I was able to talk a little about some of the adaptations, but knowing you and your expertise in sort of the seabird world, where they don't necessarily have access, ready access to to freshwater, I thought it's a great topic to discuss with you. So that's what we're going to talk about. And I guess to start with, Sarah, we don't have any well-developed notes here, so we're just going to kind of go freeform, but I want you to talk about just sort of the broad adaptations that birds have developed to cope with the environment. Like all birds need water to live. We know that. And some birds live in areas that don't afford them access to fresh water. So talk in general about some of the adaptations that birds have developed in those type of situations. Dr. Sarah Gutowsky: Sure. Yeah. I think that's kind of an interesting question because I think that there are some misconceptions about it generally. You know, when we think about seabirds that spend their lives out in the marine environment year round, they're still not drinking, you know, bill loads of salt water on purpose to meet their water requirements. And I should say that I am by no means a physiologist. So I am speaking from my general ornithological knowledge here. But, you know, you might want to fact check me on the physiology front. But all to say, you know, not even seabirds or sea ducks are drinking big bill loads of salt water, but many could if they absolutely had to. So birds in general have all sorts of, like you were saying, different adaptations or mechanisms, either that's physiological or behavioral, to sort of maintain their osmoregulatory balance. So, you know, that freshwater need that they all have. And one of the physiological adaptations that birds have is that they're very good at pulling water from their food. That means that, you know, for seabirds and sea ducks, the food that they eat actually has very, very high water content and they're very good at extracting that fresh water from their food. But, you know, what salt water they do ingest, whether that's on purpose or by accident, they can process the salt out of it using this built-in desalination system that we refer to as the salt glands. So that's what birds are doing. And really, birds that spend any time at all in the marine environment, and that includes migratory ducks, they have this pair of nasal salt glands above the eye. that perform one of the kidney's main functions, which is sort of trying to draw salt ions out of the bloodstream. And they have these salt glands because bird kidneys are actually really bad at doing that. The kidneys of birds have a really low concentrating ability, and they're just not able to produce urine with a really high sodium concentration. So that's the big physiological adaptation. And we know that there are I think it's 17 out of 25 orders of birds have salt glands. So it's a very high proportion of birds. It's basically any order or lineage of birds that there are some species that spend any time in the marine environment, they do have salt glands. But how active or developed they are kind of depends on how much a species or even an individual spends, how much time they spend in the marine environment. So the capability is there for most duck species, all duck species, but how good, how efficient their glands are and how developed they are kind of depends on It's very contextual, I guess. Mike Brasher: So for our listeners, would they be able to tell if they're looking at different duck species, would they be able to tell based on some aspect of the physical appearance whether an individual species is likely to have a well-developed salt gland? Dr. Sarah Gutowsky: Not really, no. It's kind of like it's hidden. So it's above the eye. If you looked at the skull of a bird, you can actually see it. So especially in seabirds that spend or sea ducks that spend the entire year basically in the marine environment. So take like a common eider or a penguin or a puffin, for example, you're actually going to see in the skull of a bird a well, like a very developed cavity almost above each of the eyes and that's where the salt glands sit. And what they do is they result in this like extra renal route for excretion of excess salts. So you know, outside of the kidney route, here's how we're doing it. And so the way that they're situated above the eyes, they connect via ducts to the nasal cavity And then this hyper saline solution that's produced drips out of the nostrils and then down a groove off the tip of the bill. So that's why you might see a gull that looks like it has a runny drip on the end of the nose and some sea ducks as well. And they'll shake their heads often and water flies off. That's actually this like hyper saline solution. So if you're looking at a sea duck, or a duck and it has a drippy nose and it's on the coast, you can pretty much assume that that is that really salty solution coming out of the glands above its eyes. Mike Brasher: I wasn't aware of that and that might explain one of the observations that I made this past summer when I was up on the YK Delta in Alaska and we were looking at Brant were also some emperor geese and we would see sort of a drip from their bill and we would see them shake their head and one of the things that was on my mind at that time was avian influenza and I know one of the symptoms of avian influenza is mucusy discharge and I thought that might have been what was going on because I know in the previous year there had been avian influenza effect that colony, but this is also perhaps a more likely explanation of what I was seeing. Dr. Sarah Gutowsky: If they were in a marine environment at all. Mike Brasher: Yeah, very close to it. Right at the edge. Oh, were they? Dr. Sarah Gutowsky: Okay. All right. Then, you know, it might be both going on. It'd be really hard to disentangle the two, but it could be an alternate explanation for sure. Yeah. Mike Brasher: And so with sea ducks, scoters, Let's say king eiders, any kind of eider. You see the well-formed base of the bill. Is that where, is that sort of as a diagnostic sort of feature on sea ducks? Is that where the salt gland is? Is it the size of the, of the bill, the base of the bill and the shape there? Is it associated with the salt gland at all? Dr. Sarah Gutowsky: Not at all, actually. No, because you've also got harlequin ducks or mergansers, you know, they're all in the sea duck tribe. They're not really falling into that or even the scoters kind of have like a, other than the knob on the top, which is just a sexual ornamentation, you know, they don't really have a big honking bill like an eider. That's really, those big strong triangular bills are for crushing muscle shells. They're more for that like mechanical breakdown, I think. the actual gland itself is sitting in those you know orbits above the eye so like this depression that is just in the skull essentially above the eye and then the salt excretion is happening just down like a little duct very very small little tube that's going to be going to the back of the nasal cavity and then dripping out the nostril which sits on the outside of the bill and runs down that groove to the tip. So, bill size doesn't really affect their ability to do it. I mean, think about some of the seabirds that are also using the same sort of mechanism. You've got little storm petrels that have like the tiniest, tiniest little bill, but they are 100% of their lives at sea. Mike Brasher: And they don't have their protuberance, yeah. Dr. Sarah Gutowsky: No, no, they just… It's all inside the skull, essentially, and then dripping off the end of the bill. Mike Brasher: I'll be honest, I didn't realize that. I thought there was some association with the shape of the bill. And maybe that was the salt glands were behind there somewhere. But that's just then you're saying that's just sort of a flip for eiders and scoters. That's sexual ornamentation. And it's mostly just a fleshy cartilaginous type of development. Dr. Sarah Gutowsky: Yeah, like keratin, like our fingernails, the stuff that the bill's made out of all that is just sort of that flashy stuff like on a puffin or on a scooter has nothing really to do with the salt glands because the salt glands are above the eyes. So away from the bill, really. And then they're just connected to the to the nostrils. And that's kind of it. Mike Brasher: Sarah, what do we know about species that don't regularly occur in marine environments or salty water and their ability to periodically tolerate saltwater? And this kind of gets to the question that I was asked last year. It's like, okay, can ducks that make it to South Louisiana that typically encounter fresh marsh or intermediate marsh with very low salt concentrations, what are they going to do? Are they going to be able to cope at all with this much higher salinity water that they found themselves in? And the same will extend to even ducklings, but we'll maybe go there in a moment. But yeah, what do we know about species such as mallards or pintails or wigeon and how they're able to cope either through the development of salt glands or existence of salt glands or any other type of adaptation? Dr. Sarah Gutowsky: Yeah, well, that's what's actually one of the cool things about the salt glands and honestly, any of the the organs of a bird because they're not usually like functional and active and enlarged unless they're being actively used. So, you know, even the reproductive organs in migratory birds, you know, shrivel away to like nothing outside of the breeding season because it's all about staying light for migratory birds. Right. ducts included. So, you know, they don't bother with putting, you know, weight into organs that they aren't actively using. And it's the same for the salt glands. So salt glands don't continuously, you know, function like the kidneys. They become active only in response to osmotic load. So if you're in a saline environment, your glands are going to become active. And there's the size and the capacity of the glands reflects the experience of a species and an individual with saltwater. So salt glands are larger and more efficient in species and in individuals that are exposed to higher salt loads. that's what's happening when ducks are finding themselves in a hypersaline environment without any access to fresh water is that they may be able to cope to some extent by increasing the number of cells and the efficiency of those cells in their glands. And that's what happens in experiments like with mallards, which is kind of our our go-to species for experiments, right? So you take a mallard duckling that's never been exposed to excess salt and you osmotically stress it. So you give it a really high salt content injection or just, you know, get it to drink some high salt water. And the nasal glands will start to secrete a sort of moderate hypertonic salt solution. But the performance is kind of meager. But within 48 hours, the number of cells per gland is two to three times what it was on that first day and the cells in the gland start to differentiate and acquire full capacity. And it's like a crazy adaptive growth and differentiation of cells in an organ that leads to this really high efficiency of salt excretion. So the glands show this incredible flexibility, phenotypic flexibility. And that's kind of what's going on. I mean, when you have birds that are finding themselves in these crazy hypersaline habitats. uh the first thing they're going to do you know in the case of a drought where there's no fresh water available like normally those birds would be going and and um accessing fresh the nearby fresh water and bathing and drinking like crazy when there's none available at all they're going to probably try to take prey and forage that have the lowest possible salt salt content so they're going to be really selective with the food that they eat uh and they're probably gonna you know try to limit how much free salt water is ingested when they do consume food and they might even have to you know completely behaviorally adjust like they might reduce their food intake entirely just to try to reduce that salt intake because maintaining those like big active salt glands is energetically expensive and it's not going to be super efficient as efficient as it needs to be for that kind of salt load that they could be taking on. So I think probably, you know, those high salt loads are going to lead to compromised feather growth and maintenance and they might not, you know, be able to complete a full molt, for example, and they might end up having to skip breeding the next year because their body condition is going to be low. and they may have reduced immune response as well. So they can handle it and it might not lead to mortality, but it's going to be stressful. But they do have some ability to adapt. Mike Brasher: I worked with mottleducks a fair bit when I was on the Gulf Coast and there were some pretty well-known studies by Anne-Marie Moorman, who is the wife of former chief scientist Dr. Tom Moorman here, and one of the things that she looked at was the ability of mottleduck ducklings to tolerate different levels of saltwater. Because that's a concern in coastal environments, especially where there's the potential for seasonal drought to occur and elevate salinities in some of these marshes that are so important to model ducts. And so what she found was that there is a potential, there is sort of a… a threshold above which physiological stress does occur and then if you continue to expose ducklings to higher levels then it can induce mortality. Now that was a captive setting and so you were restricting their intake to only saltwater of certain concentrations and that information has been really… foundational to some of the management recommendations for habitat, habitat management recommendations for model ducks along the Gulf Coast and basically saying that it's best if we can provide fresh to intermediate, maybe even brackish marsh, brackish water for model ducks during the brood rearing season to make it easier for ducklings to cope in those, in that landscape. And one of the things that we oftentimes see though is, I guess, evidence that would contradict We would make observations in the wild that would contradict some of what we thought we knew based on those captive studies where we would see ducklings living and persisting in some of these very high constant, high salt, high salinity wetland units as a result of let's say periodic drought. People are thinking or wondering where are they getting their fresh water? Do they develop the ability, as you're talking about, that rapidly to cope with that salt water through the better development of salt glands even at that young age? Or are they able to supplement through either collecting dew from vegetation or through the water that they would be taking in as a result of some of the things that they eat. So is that like in theory there is some upper threshold, right? At some phase of life beyond which they can't cope, yeah. Dr. Sarah Gutowsky: Especially for ducklings, yeah, exactly. Especially for ducklings and it makes sense that you'd see high mortality of ducklings that are in a really hyper saline environment even because even sea duck ducklings need to be typically led to fresh water normally the hen will lead them to fresh water to have fresh water right away on you know day one or two after hatching because they they don't have that ability yet developed so it takes time and even for a sea duck which is you know genetically predisposed to having efficient salt glands. It takes time for the ducklings to develop that ability and that efficiency. So for species that, you know, ducklings aren't normally in a, you know, marine environment. right away, that would be very stressful. But they could, you know, theoretically, just like we've done with mallards and model ducks, as you say, you know, they could probably develop the ability to adapt more quickly. And those ducklings that do that, you know, behaviorally and physiologically would be the ones that would survive. And perhaps that would, you know, perpetuate over time, but it would take a long time. And in the meantime, sure seems wise to ensure that they have some access to some sort of freshwater. Mike Brasher: One of the other species that is featured very prominently in any discussion of salt ingestion or salt tolerance and adaptation to hypersaline water is redheads. Down on the Gulf Coast and the Laguna Madre, it's a hypersaline lagoon system where at least traditionally or historically salinity levels could reach 60, 70, 80 parts per thousand during drought and even higher than that And one of the… One of the important features of that Laguna Madre system is that it's well known for these vast beds of shoal grass and that is the shoal grass, the rhizomes from shoal grass are the primary diet item, food item for redheads that winter along the Laguna Madre. The Laguna Madre of Texas and Mexico will account for somewhere between 60 to 80% of the wintering redheads in North America during any given year. And so if you're feeding on shoal grass rhizomes that are growing in hyper saline conditions and even now with some of the changes to that system you still regularly see salinity levels that exceed sea strength saltwater. We're talking 40, 50, 60 parts per thousand. You have to be real careful with your fishing equipment and your boating equipment or your gun or whatever it may be. in that environment. Great Salt Lake would be another example of a very hypersaline system. But redheads have the ability to some extent to… they have the salt glands, the same as what you've described, but one of the other important adaptations that they've developed is more behavioral. It's not just redheads, we see it in pintails, wigeon, other species that feed on shore grass or on any of the foods in that hypersaline system. they need supplemental dietary fresh water and they typically get that in that location from some of what we would call freshwater ponds. They're this vast system, pretty impressive system of ponds that exist in the lower Texas coast on the barrier island there off the coast of Texas and of course they only hold water when it rains and we get abundant moisture, but when they have water, It's really impressive to see the massive number of redheads or pintails, widgeon, any other species that concentrate in those freshwater ponds. And so that was another important conservation recommendation for that area is to protect and restore those vital sources of freshwater because those ducks have to have that to supplement their freshwater intake. Are there any other species, Sarah, or situations where you know that to be common, sort of a behavioral adaptation to go to forage in some hypersaline waters and then seek out dietary freshwater? Dr. Sarah Gutowsky: I don't know about hyper saline environments with other species. Not so much. I think there's some of these unique ecosystems where that's the case. And I mean, the the individuals even that are, you know, which is, as you say, like 80 to 90 percent of redheads that are doing that, they they have to have these physiological adaptations, but then also also require the supplementary access to to fresh water. But as far as you know, a lot of the sea ducks don't necessarily aren't in hyper saline environments, but do, you know, get most or all of their food from the marine environment. But they will still also go and supplement absolutely from from freshwater environments because they can. And I don't know about other hyper saline ecosystems where that's happening for particular species but I mean where you're talking about seems like a fairly unique scenario and I'm not sure what the consequences are of the loss of that, that freshwater access. And I know that in, you know, years with extreme drought, the birds are still there. My, my guess would be that they suffer body condition wise, and they probably have carryover effects in the next year or the next two years. For sea ducks, those things aren't as dire because they're longer lived. So, you know, that's one of the main differences between, you know, non-sea ducks and sea ducks is that sea ducks kind of live long and slow. And some of our you know, more freshwater ducks live, live, live really fast and hard. Um, so they have a short lifespan. And so there's a, it's a big deal if they have, you know, a bad body condition year and they can't breed because that's their lifetime reproductive output essentially. But for a sea duck, they could, they could take a year off of breeding. They don't necessarily breed every year. So quite a different, quite a different scenario when it comes to these two sort of groups of ducks. Mike Brasher: Sarah, I don't know if there's any more sort of adaptations that we need to talk about, but any other species stand out to you across the entire spectrum of birds in their adaptations or existence in the face of these kind of salt stresses? Redheads are a great example in the waterfowl world because of what we just described. Any other birds that really stand out because of where they live and what they have to cope with? Dr. Sarah Gutowsky: That's an interesting question. I mean, I think for me, and you know, I have a I have a fond spot for pelagic seabirds and what they managed to do because out in the pelagic environment, which is like offshore, you know, beyond the continental shelf, we're talking deep water habitat in the marine environment where if you looked around if you were out on a ship in the middle of where know, albatrosses or storm petrels are making a living, you would say there's nothing here. It's just a vast, you know, marine desert, essentially. And food in that environment is super patchy and ephemeral. You know, it's not, there's not this predictable resource that's always there, you know, a little buffet to visit. They have to find the food in this seemingly, you know, void of landmarks, you know, environment. And they use their noses and the sense of smell of these birds for finding food in this environment is something that just absolutely floors me and it always has. So for me, that's sort of a big group of species that stand out and that's sort of the primarily the tube-nosed seabirds from albatrosses to storm petrels that are making a living in what seems to be, you know, a really hard environment where they need to forage, you know, hundreds if not thousands of kilometers on a single foraging trip to come back and feed a chick. because they're exploiting resources in this environment that requires extraordinary efficiency for flight to be able to search and find these little patches of food out on the ocean. They fascinate me. Mike Brasher: So you mentioned the phrase, the category of birds, tube-nosed seabirds. Is the tube-nosed adaptation or feature an adaptation to any of the salt that they have to deal with? Dr. Sarah Gutowsky: We don't really know. exactly what the function of the tube nose is. And it's basically just like a hard, it's an extension of the bill that is a tubed nostril encasing. And one of the things that it does is it leads that excreted hypersaline solution from the salt glands down the groove of the bill to drip off the tip of the bill. But another possible explanation is that it helps to concentrate odors from the environment and they have you know the birds in this group the tube noses they have a very very well developed olfactory bulb the smell organ is gigantic in these birds compared to other species of birds. So it might be a smell concentrator. It might also act, this is the coolest theory for me, it might also act as a like a pitot tube in an airplane where it helps to detect very very minute changes in pressure and that's critical for birds that rely on wind. and pressure gradients for efficient soaring. So if you're a bird like an albatross that doesn't want to flap its wings if it doesn't have to then they just ride these like wind gradients which are essentially pressure gradients up and down across the open ocean and that tube might actually serve that function kind of like on an airplane where we're collecting information about pressure using a pitot tube. So that's one of the theories but we don't really actually know Mike Brasher: That's something else for you to figure out. Questions that remain to be answered. Sarah, I think we'll wrap it up there before we head off down into any other little rabbit trail and start talking about other things of neat features and adaptations of migratory birds in these vast landscapes. pelagic seabirds and we'll save some of that for another episode but I appreciate you joining us for today and sharing some insight on what you know and what you've learned from your experiences and your training and I appreciate the question that I got from one of our listeners last year asking about these things and I think that's just another example of how our members, our supporters, We love these animals, we want to conserve the habitats that they depend upon, and we're always thinking about the different challenges that they have to deal with and wondering are they going to be okay and what are they going to do in response to this? Will birds get to the coast and find a dry landscape and find only salt water and not be able to tolerate that and have to leave just because of the absence of fresh water? And so we've heard here that they do have some adaptations, they have adaptations as ducklings, they have adaptations as adults, both physiologically as well as behaviorally. and that continues to provide things that fascinate us about them, and as we discussed here, lots of other things to study. So, Sarah, thank you again for joining us. We're going to have you back sometime in the future. We'll have to figure out what topic we want to discuss next with you, but enjoy your spring and summer, and we look forward to catching up with you again. Thanks for joining us. Dr. Sarah Gutowsky: Thanks so much for having me. Mike Brasher: A very special thanks to our guest on today's episode, Dr. Sarah Gutowsky, quantitative wildlife biologist with Environment and Climate Change Canada. We also thank our producer, Chris Isaac, for the great job he does with these episodes and getting them out to you. And the listener, we thank you for your time. We thank you for supporting the podcast and for your commitment to wetlands and waterfowl conservation and science. Don't forget science!