Super Hens: The Experts Speak
The sources below provided information on the examination of the vital impact “Super Hens” have on the health of the nation's duck populations for the 2020 Greenhead feature, Dead Ducks Don’t Lay Eggs
A PDF copy of "The Super Hens" by Mickey Heitmeyer, Ph.D., of Greenbrier Wetland Services is also available for downloading.
Todd W. Arnold
Professor of Fisheries, Wildlife, and Conservation Biology
University of Minnesota
I'm not in one extreme camp or the other on this subject (too extreme is usually wrong, in my opinion, especially if both sides are providing sensible arguments).
What I know from analyzing radio telemetry data and band recovery data from adult female mallards is that they mostly die from just 2 things: predators like fox, mink and raptors during the nesting season (and this is the biggest loss) and hunters during the hunting season. I can't think of any realistic ecological explanation for how hunters shooting female mallards in the fall and winter is going to greatly reduce the number that predators take during the nesting season, so compensatory mortality is hard for me fathom (it can make sense for juveniles, that die of natural causes during the winter, but not for adults). But by the same token, there's no way that if a hunter passes up on a hen, that hen is going to get a free ride from foxes during the breeding season. For adult hen mallards, about 1 in 3 or 1 in 4 is going to die anyway of natural causes, whether or not they get hunted. So if you know somebody who kills 10 adult females during the season, maybe about 3 of them would have died anyway, but the other 7 got removed from the breeding population. So it does matter, but not on a bird for bird basis.
But there are some other things that reduce the impact of shooting hens. In a typical fall, there is just under one juvenile hen for every adult hen in the hunted population (long term average is about 0.8 juvenile hens per adult hen mallard). But the juveniles are 2-3 times more vulnerable to hunting (they're not as wary), and so if you decide to shoot a hen mallard, you can't tell if it's an adult or juvenile when you shoot, but it's more likely to be a juvenile, and shooting it will have much less of an effect on the population because juveniles don't survive as well from natural causes, and they aren't as good at producing young if they do survive. Shooting an adult hen is probably twice as bad, from a population perspective, as shooting a juvenile hen. But even if you do shoot an adult hen, it can create an opening for a juvenile hen to take her place. It's not a perfect replacement, but it's not a total loss either.
Because we have a lot more males than females in all duck species where we know the sex ratio, there's really no harm or concern about harvesting males at the level that we do. And I'd argue that even if you break a pair bond on the last hunt of the season, there's still plenty of time for the hen to repair before nesting season, and no shortage of males that are willing to be her mate. And killing more unpaired juvenile males might just free up some resources to help the juvenile females (lowest on the dominance totem pole) survive better from nonhunting mortality.
I've lived in Manitoba and Saskatchewan for several years of my life, and had phenomenal duck hunting. I've been able to be choosey, and I've prided myself on shooting only males in those situations (and for species where it's reasonable to tell them apart - so, not fall bluewings). But I've lived in Minnesota for the last 20 years, and I don't always have the luxury to be selective. Presented with a choice from a flock, I always try to go for a drake. If I know it's not the only bird I'm going to see, I let lone hens land in the decoys if they want to. But on slow days in Minnesota, if my choice is to come home with a hen mallard or nothing, I'll sometimes opt for the hen. I'll hope it's a juvenile when I shoot, but I won't know for sure until it's in hand. Given how little color our birds have when the season opens in late September, sometimes it will even turn out to be a juvenile male that I can ID in hand only from the bill. How is a first year duck hunter ever going to make that call?
So, my opinion, be selective if you can, and take satisfaction from it if you can. If you kill a lot of ducks in a season, it will make some amount of difference, even though we could never measure it as biologists. If you can't be selective (your ID skills aren't that good yet, you just don't have the opportunity), don't lose too much sleep over it. You probably don't kill that many ducks in a season anyway, and there are some other ecological things that I've mentioned above that will compensate for the impact of shooting a hen. The mallard population as a whole is certainly doing fine, and can overcome the losses in other ways.
J. Brian Davis
James C. Kennedy Associate Professor of Waterfowl and Wetlands Conservation
Mississippi State University
The fascinating things as you learn more about demographics, disease, survival rates, etc. is that no two individuals are the same – as Mike mentioned. As young wildlife biologists, one tends to focus on this occurring at a SPECIES level – ie, mallards are (seemingly) much more adaptable, or have mechanisms built in (or gained from experience) that enable them to sustain higher breeding ground success, or annual survival than do pintail. But even WITHIN species, no two individuals are exact. Some pintail die during their first fall migration, whereas others may get shot at age 14. Some humans are plagued their whole lives by disease, whereas some die at 100 with few complications. It is this way from giraffe’s to gerbils---and swans to hummingbirds. And think about snow geese and white-fronted geese. The demography or selective pressures in snows arguably occurs at the colony level, because these birds are somewhat “Protected” or buffered in these huge colonies by one another, nesting together by the thousands. But in WFG, many of these birds do not nest in colonies, per se, so the selective pressure operates much more “Individually,” at least while nesting. Individual WFG in times and places may be much more vulnerable than are white geese.
In terms of “Super hens,” I am a believer in this concept. But as Mike said, it is difficult to quantify. We would have to literally have thousands of hens marked with GPS radios and follow them annually, and basically assume there are few to no radio effects. We could study these birds annually and examine survival, nesting and recruitment, etc. We often acknowledge or think of “Super hen” as a nesting phenomenon. Although I think possible and true, I am a firm believer that what equips a hen to be “Super” while on the nest, is also built in to her survival during winter, and hence avoiding being shot, for example. Again, although I am convinced this happens, quantifying that is nearly impossible right now (at a large scale, with many dozens or hundreds of birds). So, I am here to say, I do NOT have the data, but I believe strongly that these things occur. How fascinating one day to unravel these dynamics. Some insight into this has become evident in some of Dr. Todd Arnold’s banding analyses (my next email to you).
So yes, natural selection works at the individual level, and no two animals or people are just alike. Although in some birds, perhaps even wood ducks, there may be some aspects of kin selection that occur among nesting colonies but we are still figuring that one out. In other words, some accommodation of nest parasitism by grandma’s, moms, aunts, daughters. Eadie will be the fastest one to figure this out bc of the thousands of birds he has marked, and basically no natural cavities in the Sac Valley (compared to eastern North America)----if a hen survives winter, about 99% chance she returns to a nest box.
And last. We often think of harvest as some binary phenomenon, such as additive or compensatory. However, “partial compensation” too is often used, and I believe in this “Softer” distinction, at least for most of the time. When winters are wet as hell and mild, duck survival is pretty good. When cold and dry, ducks can become vulnerable. But there is all that “In between” that is interesting. And that leads into Todd Arnold’s assessment. Basically that, no, mallard harvest is not additive to the point that populations are affected. But, if we refrained from shooting x% of hens during winter, this DOES translate into a x% recruitment the following spring. Again, it may not make the BPOPS jump up, but his point is (and I agree) that “These surplus hens would have died anyway” (from natural mortality) is not necessarily true. I agree with his statement. So, yes, refraining from killing 2 hen mallards every day may not create some noticeable spike in overall BPOPs the following spring, but some of those hens that are not shot will breed, AND will recruit future female mallards.
As you say, this is a complex topic, and for that reason, an easy, concise, and confident response is hard to come by. A couple of quick points:
Your observation of those 2 different size broods may or may not reflect the concept of a super hen. A single observation of that type may have simply been the product of random chance events with respect to the many things that can influence clutch size, hatching success, and then duckling survival. However, if you happened to see those same 2 hens each year for the next 3 years, and in each case one hen consistently produced more ducklings, then you would have the beginnings of support for one being a better “producer” (i.e., super hen). The way I see it, the concept of a “super hen” is best applied to demographic rates over a bird’s “lifetime.” In ecology, we often speak to fitness as being best evaluated based on something called “lifetime reproductive success.” LRS is pretty hard to measure, although Brian can speak to what we might have been able to learn from wood duck studies where are ability to recapture hens year after year is way better than say for mallards, so we don’t have a ton of information from which to evaluate a super hen concept. But with that said, there is no question that individual ducks and geese differ in their behaviors and demographic rates. Personally, I see no reason to question the idea of there being some hens that are consistently better survivors and better producers than others. After all, that is the basic mechanism behind natural selection and the evolution of species traits. I’m not sure of the empirical threshold that what would constitute a “super hen,” but individuals clearly differ in their contributions to annual recruitment. And if those differences are maintained for multiple years, then you begin to have stronger evidence of this idea that over the long term there is some small percentage of the population that is disproportionately important for overall annual recruitment. Where things get really interesting is if we could demonstrate that those differences were inherited. That’s where my understanding and commentary should probably stop. I know Dr. John Eadie is conducting some fascinating research on wood ducks in California that will help us answer these questions with greater certainty, at least for wood ducks. On this note, I recently recorded a podcast episode with John on this work of his, and we briefly touched on this topic in that conversation.
Senior Vice President
We need to remember that ducks are product of a highly variable environment (certainly from a production perspective) and their ability to capitalize on good conditions is what gives us high recruitment and large fall flights. There is no doubt some hens are way better at being successful breeders than others, but when we have the right wet conditions on the prairies (oh yeah and still have the ponds to catch the moisture) I bet the difference in per capita recruits (between good hens and bad ones) may be less important. When we have wet conditions, I bet even crummy hens have high hen success simply due to the strong re-nesting rates we see on wet years and also much higher brood survival seasonal wetlands. In a year like this, where we have ducks taking advantage of very good wetland conditions in the eastern Dakota’s and some ducks being in droughty Saskatchewan. I am pretty confident their reproductive output is influenced far more by wetland conditions where they breed.
I had the chance to read Mickey’s original Super Hen paper probably 15 years ago. One thing that fell flat for me is that it seemed to miss the variable environment described above and its influence on production as well as the inference that a females job was to replace herself in her lifetime. I think ducks are a lot more like field mice than elephants. Relatively short lived, high reproductive potential…So the life history of ducks is to make a pile of young when conditions are good. If female ducks only replaced themselves, we would have far less ducks today than we do in the breeding population and that certainly isn’t the world duck hunters are after. When the prairies are wet, we can see crazy good age ratios (immature to adult) See graph below:
This graph uses the mallard BPOP plus the age ratio in the harvest to “back calculate” the mallard fall flight. If you look at 2014 and 2017 you see the mallard BPOP is very similar, May ponds were higher in ‘14 as was the age ratio. Look at the difference in the green line the “mallard fall flight” same BPOP but almost 30% more mallards in the fall flight in ’14. Wet prairies really drive the machine and I don’t think much else even comes close…
Waterfowl Program Coordinator
Arkansas Game & Fish Commission
But to play devil's advocate as a guy who spends part of his job dealing with regulations, what choice do we have? We haven't really had an alternative modeling framework available, but we did recently change AHM to use an integrated population model that should, over time, give us a much more complete understanding of population dynamics. We're not there yet, though.
Likewise, what can we do regulations-wise about "super hens"? The very premise of a super hen (great at avoiding mortality, including from hunting, as Brian states) suggests these birds will be adept at avoiding harvest anyway (current harvest rates on adult female mallards is less than 6%). And hunters can't tell what type of hen it is when pulling up on one when she's over the decoys. Lowering female mallard bag limits would undoubtedly keep some hens from getting shot. To what extent, however? When we hashed out increasing the hen mallard bag limit from 1 to 2 back in 2008, we calculated that we could expect to harvest an average of 31,000–61,000 additional hen mallards (25% increase) each year with a 2-bird bag limit, probably closer to 31,000 unless we have some extraordinary harvest years like 1999-2000. That's not many birds out of a population of ~10 million. So it's not easy for waterfowl managers - who must manage at the population scale, in this case midcontinent mallards - to get excited about what are seen as restrictions when available information about demographics don't indicate a population-scale issue.
Now check out immature female mallard harvest rates since 2000 and my curiosity rises. You'll see an even stronger signal when looking at differential vulnerability since 2000, but I couldn't find those figures right now. Spinning-winged decoys anyone? Alas, for another day...
To argue the other side, however, I'll go back to Brian's statement: "So, yes, refraining from killing 2 hen mallards every day may not create some noticeable spike in overall BPOPs the following spring, but some of those hens that are not shot will breed, AND will recruit future female mallards." And where might these future female mallards migrate and winter? Likely to the place they successfully survived past winters. So this becomes a more local issue, but still one that's damn hard to argue (and set regulations for) without strong empirical data. Which Mike and Brian made clear we don't have. And I agree. Like many ecological questions, it's an issue of scale of management vs. of scale of inference. We manage waterfowl at huge scales but we, as hunters and biologists, often observe at much smaller scales. Therein lies the rub
I'll end this ramble with one example anecdote of those regional impacts. Ken Reinecke is retired now, but worked for USGS in Vicksburg, MS and was one helluva mallard researcher whose work doesn't get discussed enough in my opinion. When I moved here in 2006, we were climbing out of the most recent duck apocalypse of the day, namely the early 2000s, as hunters lamented an apparent decline in duck numbers. Ken quipped that these ducks were gone because the same AR hunters shot them. They shot them in 1999-2000 and 2000-2001 during unusual conditions and with the use of new gadgets. Maybe this is one instance during which "super hens" were harvested at unusually high rates and migratory connections were broken. No one has any data to prove that.
In summary, certainly vital rates differ for individual mallards but we don't have broad evidence to show how, where, why and at what scale it matters; partial compensation is probably a better way of looking at waterfowl demographics; and, differential survival may have greater impacts on populations at local or regional than continental scales.