Delta student researchers looking for answers

By Dr. Elizabeth Loos
Research Director

Delta Waterfowl’s past research has clearly demonstrated that reducing predator numbers during the breeding season has a dramatic impact on nest success on prairie habitats in North Dakota and Saskatchewan. This year Delta will examine the impact of trapping on the Canadian parklands.

In the late 1990s Pam Garrettson’s pioneering research showed that trapping just about doubled nest success in the North Dakota. Subsequent work by Mike Hoff, Vance Lester, Kristen Chodachek, and Lucas Oligschlager corroborated Pam’s findings. In each case nest success on trapped blocks was about twice as high as on non-trapped blocks, regardless of whether the trapped blocks were large (36 square miles) or small units (1 square mile) or in North Dakota or the prairies of Saskatchewan.

The consistency of results about nest success is reassuring to managers, but some might wonder if trapping can work in other habitats and for other species.

The all-important Prairie Pothole Region is actually comprised of two fairly distinct habitats. The bigger southern segment is prairie, which is where Delta has done all of its experimental work on predator reduction. North of the prairie is a wide strip of habitat that is called parkland habitat, a broad transition between grassland habitat and the great forested boreal habitats.

Accordingly, the parkland has lots of trees, locally called “bush.” In recent years, it has become fairly evident that parkland and prairie habitats are quite different. The parkland’s more stable wetlands don’t dry out as often as prairie ponds. More importantly nest success, predators, and duck productivity appear to be fairly different in the parklands.

Last year we initiated a study looking at predator reduction in the parklands. In this study Southern Illinois University master’s student John Dassow is looking at nest success on trapped and untrapped blocks in the highly productive parkland region in central Saskatchewan.

John has added an interesting twist to his research: He is looking at whether ducks are capable of assessing predator abundance and placing their nests in areas with fewer predators.

John will spread urine on some fields and not others, then he will assess how many nests females initiate in each field. This may sound far-fetched, but field studies suggest some birds are capable of detecting mammal urine in fields and adjust their foraging accordingly. And John’s advisor, Mike Eichholz, has found that captive mallards appear to avoid areas where he distributed fox urine. The next logical step is to look at whether fox urine will influence wild populations.

For the past two years Matt Pieron (Ph.D. student, Louisiana State University) has been using the numerous predator-reduction blocks in North Dakota to test for density dependence in ducks. In many wildlife populations the reproductive success is low when the breeding population is large. That’s what scientists call density dependence, a natural force that tends to regulate population size. Matt’s work will test for the effects of duck density on duck reproduction.

Matt built his research on the observation that nest success, the key driver of duck production, is much higher on trapped blocks. Accordingly, he assumed that production was greater on trapped blocks, which theoretically would mean a larger population of nesting ducks in subsequent years if the hens showed normal homing.

First Matt had to assess population size on trapped blocks and on non-trapped blocks. He expected higher numbers of ducks on trapped blocks and more breeding pairs on blocks with a long history of trapping. Two years of data have suggested that pair numbers are only slightly higher on trapped areas than on non-trapped control sites, and that was a surprise.

Matt has come up with two alternative explanations for these findings. First, it is possible that trapped sites actually don’t have greater production than control sites. That seems unlikely given the well documented differences in nest success, but it is worth considering because nest success is not the only important component of production.

Fortunately, Courtney Amundson, (Ph.D. student, University of Minnesota) is continuing her detailed work on brood survival (started in 2006), so we should have a good understanding of production from trapped blocks.

The second feasible alternative is that trapped blocks produce more ducks, but in subsequent years those extra hens disperse to areas outside their natal area for nesting. This hypothesis suggests that the well documented pattern of philopatry — a.k.a. homing — by female ducks is actually dependent on the size of the local population.

Matt suspects that an increased number of females home to trapped blocks. But, he believes it’s possible that those females that arrive first exclude hens that arrive later. Matt’s emphasis is to record the spacing behaviors of dabbling ducks, especially mallards, to discover the role that pair spacing may play in population processes of mallards.

Matt’s work and work by former Delta students, such as Dan Coulton (Ph.D., University of Saskatchewan), suggests that duck dispersal was an important component of waterfowl biology. However, the topic has not been the subject of a great deal of work because of the technical difficulties of measuring dispersal.

New Delta student Laura Beaudoin has taken on the challenge for her Ph.D. research at the University of Guelph, Ontario. In July, Laura will capture and mark juvenile female mallards on trapped and control blocks in North Dakota, then track fall and spring dispersal of the birds.

Older females tend to return to their nesting area earlier than first-year birds, so she will be able to look for displacement of later-arriving, first-year hens. She will implant radio packages with some sophisticated circuitry that will shut them off in the fall so that they are dormant all winter to save battery power, then around March 15 the radios will reactivate.

The big question is will Laura be able to find her hens somewhere near the site they were marked? If Matt’s hypothesis is correct, the hens raised on the trapped block will come home, but find their natal trapped block crowded. They may get chased around by the earlier arriving adult hens and disperse to adjacent habitats where the pair density is lower. In contrast, we expect the birds from the non-trapped control blocks to home to their natal area and be more likely to stick around.

Laura’s work also has a fall component. For all the interest in mallards in the fall, there has been remarkably little study. We have banded hundreds of thousands of mallards, but almost nobody has studied the ecology of birds from the time they become independent in July to the time they depart from the PPR.

Laura will examine everything from how much female mallards move around to whether their movements are consistent. She’ll examine how much hunter disturbance affects movements, what habitats the birds use and how long local birds stay on the trapped sites. If Laura can track birds in the fall and then again in the spring, she will be able to see if preferred habitats in the fall are also disproportionately used in the spring.

Two other University of Guelph students will be working on the predator treatment sites in North Dakota. Master’s student Chris Martin is going to examine the avian predators on the trapped blocks. Ecological theory and prior studies in other ecosystems suggest that when one set of predators is reduced, another set of predators fill the void. Chris’s question is: Do the avian predators pick up the slack and reach larger population sizes and/or produce more offspring on the trapped blocks, where we assume that mammalian predators are scarce due to the trapping?

Master’s student Jen McCarter is looking at the wetlands on the trapped and control blocks. Jen will measure the amount of food at each step in the food cycle, starting from the photosynthetic algae right up through the layers of invertebrates to predators like ducks, salamanders and small fish. The question is whether duck numbers or predators regulate the availability of food.

The final study will addresses the human social aspects of trapping. If a highly visible, large-scale trapping effort would increase fall flights by hundreds of thousands of birds, it’s important to understand the social implications.

Having scores of trapped sites would require a legion of cooperating landowners, so research must be conducted to help us better understand the attitudes of those landowners in the PPR.

Because a large-scale trapping program would also be fairly visible to the general public, we also need to know how the general public would react to predator reduction. It is pretty clear that waterfowl hunters would react positively and animal rights activists will never agree with such management, but what about the majority of people, those who fall between these opposing views? Because they are the majority, we clearly need to know their views. This work will be taken on by a Ph.D. student working with Dr. Craig Miller at the University of Georgia.

Space precludes discussion of many other exciting studies from around the continent: scaup in the Great Lakes and Montana, geese foraging in Oregon, wood duck parasitism in California, mottled duck survival and habitat use in Texas and Louisiana, mallard and wood duck use of nest structures in Pennsylvania and Ontario, and goldeneye broods in British Colombia (see sidebar). Once again we are excited to have a diverse program with terrific mix of motivated students and innovative projects.