Songbird field study backs win-win results of “umbrella species” habitat management

IN SOUTHWEST MONTANA, MANAGING WOODY ENCROACHMENT FOR SAGE GROUSE EXTENDS BENEFITS TO SAGEBRUSH SONGBIRDS

Conserving at-risk and imperiled wildlife is often a balancing act. Limited conservation funding and capacity can constrain projects. “Umbrella species management” is one tactic conservationists use to benefit multiple species through restoration activities targeted at a specific species.

In the sagebrush sea, for example, conservationists often use sage grouse as an “umbrella species.” Because sage grouse are so dependent on healthy, intact sagebrush for nearly all aspects of their lifecycle, they can be used as barometers of the overall health of the ecosystem. And because sage grouse have received significant funding over the last two decades, projects that target grouse are less susceptible to constraints than those for other species.

However, understanding how populations of non-target species respond to umbrella-species management is important to improving conservation outcomes. Local science, focused on specific non-target species and habitat types, is especially valuable for managers, who often rely on extrapolating results from research in different geographies.

Researcher Elise Zarri, in collaboration with Bureau of Land Management (BLM) biologist and funding partner Katie Benzel, recently published a paper in the Journal of Applied Ecology that explores just how conifer management targeted at improving habitat for sage grouse impacted other songbirds that live in southwest Montana’s sagebrush country.

They found that the more closely the non-target species’ habitat use overlaps with that of the target species, the more benefits those species realized.

We sat down with them to learn more about the study, the important role local research plays in wildlife management, and how the study’s clear results and findings are benefiting the wildlife and people who live in southwest Montana.

Katie, why was BLM interested in funding this study focusing on conifer encroachment?

Katie: There’s quite a bit of research on the impacts of conifer expansion and the benefits of conifer removal for sage grouse, but a lot of that research occurs in the Great Basin or for pinyon juniper, which is different than what we’re treating here. So, we were really interested in funding this research to get local knowledge about effects for songbirds in the habitat where we’re working.

At the Dillon Field Office, we’ve been completing conifer expansion removal every year, largely for the long-term retention of sagebrush grassland habitat. The BLM-administered land within the Medicine Lodge area, where this project took place, is mapped largely as a sage grouse priority habitat management area or sage grouse general habitat management area.

The goal with our treatment is to prevent it from converting to forest because once it goes past that threshold and the sagebrush is gone, it’s really hard to get that habitat back.

Will you explain the concept of umbrella species management for those readers who may be unfamiliar with it.

Elise: Conservation in general can be complicated. Ecosystems are complex. So instead of trying to restore an entire functioning ecosystem, we take one species that is unique to that habitat type and call this an “umbrella species.” When we do management for the umbrella species, in this case removing conifers for the benefit of sage grouse, we assume that it’s going to benefit a bunch of species that we think will fall underneath that umbrella. This management strategy leaves a lot of assumptions that need to be tested, including how well the umbrella species represents the habitat, which other species fall under the umbrella, and whether they will benefit from management action.

Sage grouse are used as an umbrella species in the West because they’re imperiled, and they’re game species, so they’ve been much better monitored for a longer time than non-game species.

We also know that they’re declining and because of that, there’s been a lot of conservation attention to try and reverse those declines. So, because they’re declining and they’re reliant on sagebrush, they’ve become an umbrella species for the sagebrush biome.

Grouse are slightly unusual as an umbrella species, in that we’re usually looking at larger species, like tigers in large parts of India and Asia. If we do actions or protect areas for tigers, it should protect a whole bunch of other species that rely on that same tropical forest habitat.

This study focuses on songbird response to conservation aimed at sage grouse, a ground-dwelling bird. Why quantify songbird response to conifer encroachment as opposed to other sagebrush-dependent species?

Katie: In the past, we’ve worked with researchers studying pygmy rabbit responses to conifer encroachment and impacts from prescribed fire. We’ve also worked with Montana Fish Wildlife and Parks trying to address concerns with conifer expansion into important browse habitat for big game.

Two of the songbirds in this study, the Brewer’s Sparrow and Sage Thrasher, are “sensitive species” on BLM’s special status species list. That list is used for special management considerations to promote the species’ conservation and reduce the likelihood that they’ll need to get listed under the Endangered Species Act.

As part of that, we really focus on analyzing impacts to those species from our management decisions, including these conifer removal treatments. Since they’re sensitive species, it’s even more important to gather information on what our management impacts really are in our local habitat.

Elise: Songbirds are so abundant and visible and there’s so many different species, so they provide a good opportunity to study both of ends of the spectrum in terms of habitat type. We could look at these sensitive, sagebrush-obligate birds, but then we could also look at what species are using this conifer encroached area – species that are more forest associated – to see if there are any negative impacts to them that we aren’t aware of.

Using songbirds gave us this unique opportunity that we don’t have with other types of animals to look all the way across this spectrum.

Katie: There are species that do use this conifer encroached or “edge” habitat, so it’s nice to have results for those species as well. While they’re not a sensitive species, they still are taken into consideration, and we want to know the impacts to those species as well. That’s another value out of this study.

You evaluated songbird abundance and demographics. What is the difference between those and why was it important to include demographics in this research? How did you collect demography data on songbirds?

Elise: Abundance is simply the number of animals in an area. For this study, we were looking at the number of each type of bird in areas where conifer removal had occurred and where it had not.

Demographics goes into the birds’ reproductive success. The reason it’s important to collect both abundance and demographics is that any species can be more abundant in any one particular place, but if they’re not more successful there, then we call that a population sink.

So, while on the surface it can look like good habitat for a species, when you dig deeper and understand the demographics, they’re actually going there and becoming less successful. 

The concern is that we could potentially be creating a sink habitat from this type of conifer removal. The birds are drawn to conifer removal areas, but in fact, maybe there’s more predators there, and their nestlings can’t leave the nest before they’re eaten. So, while they’re drawn there, there’s fewer opportunities for success. We wanted to clarify that to make sure both the abundance and demographics confirmed that we were doing something useful for these species.  

There are other studies that have looked at abundance and have already established that Brewer’s Sparrows, Sagebrush Sparrows, and Sage Thrashers are more abundant when you remove conifers. We wanted to add the demography data to make sure they weren’t being attracted to an area that was a population sink.

To collect the demography data, a crew of field technicians and I spent every day, all day, out in these areas and looked for bird nests. There are a couple ways we can do that. We can follow adults that are carrying nesting materials or food for nestlings. Or we can walk through the sagebrush looking for nests. Once we found the nests, we would then return and visit them every day or every other day, and record what was in the nest – how many eggs or how many nestlings, and whether those nestlings successfully fledged and became independent birds.

All told, it was four summers of work with seven technicians. This type of study has to be done at a small spatial scale. It’s not something you can do over a large area because it takes so much effort, and you have to go back every day to the same place.

Those were some really busy summers!

Will you walk us through the study design for this project?

Elise: We had six plots in areas where the trees had been removed from sagebrush and then six plots where sagebrush was still in the understory but there were scattered trees. It was a little bit of Tetris placing my plots on this landscape because you need to think about things like: where were the treatments done and can you access those easily every day or do your technicians need to hike in?

The plots were about 60 hectares each [~150 acres] and each technician was responsible for two plots. I was basically a “floater” and moved around to different sites.

Katie, how did the BLM work with Elise to manage conifers in the project study area during her research?

Katie:  In 2017 and 2018, through the Southwest Montana Sagebrush Partnership, which includes BLM lands, State of Montana lands, and private ranching lands, we had identified several areas where we planned to remove conifers mechanically.

Elise was able to work with The Nature Conservancy, which is helping to lead that partnership, as she was doing her research. So, they held off on removing conifers from some of those areas until Elise was done.

In that partnership there are several different land ownerships involved, but there was one point of contact through The Nature Conservancy, so that was really helpful. They were well aware of Elise’s study and didn’t remove trees where she was working.

Elise: Sean Claffey, with The Nature Conservancy, was really on top of it. He’s done a great job in southwest Montana of organizing all of these different agencies and groups and research projects to make sure everything goes smoothly. So having that one point of contact, and just the fact that the partnership exists, made it much easier than it could have been.

Brewer’s Sparrow and Sage Thrasher were the “rock stars” of this study. How did they respond to conifer management?

Elise: These are the two sagebrush obligates that we had at our study sites. And these were the two that we were hoping would benefit from conifer management. And that was, in fact, the case.

Sage Thrashers are extremely sensitive to tree presence, so we didn’t find a single sage thrasher territory or nest where trees were still present. That emphasizes their sensitivity to trees and how removing those early stages of conifer encroachment can expand space for sage thrashers.

Brewer’s Sparrows were present in both treatment types, but we saw significant increases in abundance and reproductive success where trees were removed. We didn’t see that population sink that we were worried about. They really benefited when trees were absent. Their nests were less likely to get depredated, and there were more birds around.

Overall, it was really good news for these sagebrush-obligate birds.

Katie: It was awesome to see, especially with the Sage Thrashers. I didn’t really expect that, where they’d be completely absent where there was any expansion of conifers. It was a bit surprising it was so black and white for that species.

Elise: We saw benefits for one other species. Vesper Sparrows are generalist shrubland- and grassland-associated species, and we saw significant benefits, both in terms of abundance and reproductive success. So even though they’re not sagebrush obligates, they are still going to benefit from conifer management.

The one caveat was the Green-tailed Towhee, which is often called a “near obligate” of sagebrush. And that’s because, if you look where they occur in North America, it overlaps with sagebrush, but they tend to use sagebrush with some taller shrubs or scattered trees. They do actually like this “edge” habitat, this conifer-encroached habitat. And we did see slight decreases in abundance but no change in reproductive success where trees were removed.

They might just be shifting with this sagebrush-forest edge. So, if we end up pushing that back but still create that “feathered edge,” they should be fine; they’re just moving in space. But if we go in and remove everything and create a hard edge with dense forest, that might be bad news for them. We weren’t able to test that specifically in this study, but that’s our interpretation of these results.

Katie, describe how the BLM might use the findings from this research? And what are the BLM’s plans for future conifer management to restore rangelands?

Katie: Every year, Elise would provide a report on her project with some findings, so I’ve already been using her data. Now having a published paper and the full results of her study is even better.

Under our obligations under the National Environmental Policy Act, we have to write environmental assessments on any action we’re proposing on the landscape. When we propose to remove these conifers in these areas, we have to analyze impacts, and part of my job as a wildlife biologist is analyzing impacts to these songbirds. Using her results that are occurring right here in our field office is huge. Having these results in the habitats we’re treating better informs our management actions for what the impacts are for these species.

Conifer encroachment management is a major part of what our field office implements and will be for the future. It’s incredible to have this local data to help inform these projects and what impacts we can expect.

What else would you like to share about this research?

Elise: This was such a fun project to work on. It was one of those rare times in science and conservation where you have these win-win results. You see a real benefit for the birds, which was great. And working closely with the Southwest Montana Sagebrush Partnership and the BLM and seeing that there are benefits to landowners and cattle producers for removing these conifers as well.

It’s one of those really fun stories where we can have this win-win relationship, where management action that’s beneficial for wildlife, not just birds but also big game, also has benefits for cattle and people who rely on this land for their livelihoods.

Katie: It’s such helpful, valuable information to have. There is a question with all the different treatments we do: is it really having the impact we’re thinking it does? With this research getting into the reproductive output and really understanding that, it informs what effects we’re actually having. These results are pretty clear.

We can’t do single species management, so it’s a balance of looking at the whole landscape. It’s awesome to have this local information.