Report from the 2011 Grassland Restoration Network – Part 2: Grassland Birds

The Grassland Restoration Network’s 2011 annual meeting was at The Nature Conservancy’s Kankakee Sands prairie/wetland restoration site in Indiana.  This year, we focused more than usual on creating habitat for various animal taxa, and I previously reported on the herpetology portion of the meeting.  Here is a summary of the discussions we had regarding grassland birds.

While the diversity of insects in a prairie is strongly tied to plant diversity, grassland birds have no such relationship.  The species richness, abundance, and breeding success of grassland birds are mainly related to variables such as vegetation structure, habitat patch size, and the amount of grassland in the neighborhood around their nesting sites.  At Kankakee Sands, the 6,000 acres of restored prairie/wetland habitat are obviously increasing both the patch size and total amount of grassland in the neighborhood, so our discussions focused on vegetation structure.  The ideal situation, of course, is to have a diversity of vegetation structure scattered across the site so that all grassland bird species can find the habitat they require for nesting.

This kind of tall vegetation is typical of most of the restored prairie at Kankakee Sands (and most other tallgrass prairie restoration sites). While valuable for many species, it's not much good for grasshopper sparrows and other animals that require short or patchy habitat structure.

We talked mainly about two different approaches to creating habitat structure in order to accomodate a rich variety of bird species.  The first approach is to design seed mixes for each desired habitat structure type, and the second is to design seed mixes that promote overall biological diversity, and then manage for structure with fire, grazing, and other tools.  Kankakee Sands is employing both strategies, so we were able to look up close at each.

We first looked at a restored prairie that had been seeded with about 60 species of short and medium-height plant species, and that included bunchgrasses like dropseeds and little bluestem instead of tall and strongly rhizomatous species like big bluestem.  The resulting structure was very favorable for grasshopper sparrows and other species that prefer that short to mid-height structure.  The seeding was nearly a decade old and seemed to be maintaining its structure and species composition with only a couple of prescribed fires as management.  The short patchy vegetation is definitely a contrast to the majority of other seedings at Kankakee Sands (and most other tallgrass prairie restoration sites) which are mainly tall and rank.  Those taller sites provide excellent habitat for Henslow’s sparrows and species with similar habitat preferences, but don’t do much for grasshopper sparrows.

Chip O'Leary (left) describes grassland bird habitat and research results with participants of the 2011 Grassland Restoration Network workshop. This restored prairie was seeded with short and medium-height plant species (including bunchgrasses instead of tall and strongly rhizomatous species).

The second example we visited was one of the first seedings done at Kankakee Sands (in the late 1990’s).  From the beginning, the several hundred acre prairie has been dominated by grasses and has been low on forb species diversity.  For the last several years, the Conservancy has been experimenting with patch-burn grazing as a way to create more heterogenous vegetation structure and to increase forb diversity in this prairie.  To date, forb diversity has neither increased nor decreased, but habitat structure has certainly changed.  The recently burned (and thus currently grazed) portions of the prairie provided excellent grasshopper sparrow habitat, while other portions were more tall and rank.  Though no change has been detected in forb abundance or diversity, the staff has noticed that a few forb species seem to bloom less abundantly than in the past – including compass plant, prairie dock, and Canada milkvetch.  Because of that, we discussed the value of fencing out a significant portion of the prairie each year to ensure that those species were given a complete break from grazing pressure periodically.

The two methods of creating bird habitat (seeding design vs. active management) both seem to be working well so far.  Both the prairie seeded with short/bunchy vegetation and the grazed prairie had significantly different vegetation structure than did the majority of the tall rank prairies around them – and birds are responding to that structure.  However, there are still plenty of questions about the long-term future of both approaches to creating bird habitat. 

In terms of the seeding design approach, one potential downfall is that the site was seeded with considerably fewer plant species than most other tallgrass prairie seedings at Kankakee Sands.  The potential effect of this lower diversity on insects and other species is unknown.  In addition, planting short and medium height plant species in soil/climate conditions that typically favor tall species could result in a relatively unstable prairie community.  In the long term, the fact that those shorter plant species aren’t using all of the available light/soil/moisture resources could lead to encroachment by either tall grasses (defeating the purpose of the design) or invasive species (which create obvious problems).  The planting we looked at was located on dry sandy soils with very low organic matter, so it probably is less at risk for that kind of instability than if it had been located in wetter or heavier soils. 

A final potential disadvantage of the seeding design approach is that the location of the short/medium habitat structure is static.  Grazing and other management tools for manipulating structure can be moved around a site from year to year, creating a shifting mosaic of habitat conditions.  That kind of mobility could help keep predator or pathogen populations from building up under consistently favorable conditions at any one site (this is speculation).  In addition, the staff will have to be careful to avoid repetitive management treatments aimed at maintaining the same structure year after year – that management could consistently favor some plant species over others, further reducing the plant (and insect?) diversity of the prairie.

There are plenty of concerns about the patch-burn grazing strategy as well.  To date, the plant diversity in the grazed prairie we looked at has not gone down, but neither has it increased – though increasing plant diversity in a grass-dominated prairie is very difficult with any strategy.  Because the prairie started with few forbs, it’s hard to know what the impact of patch-burn grazing would be on a more diverse plant community, but that needs investigating.  We discussed the possibility that a higher stocking rate and the addition of a large exclosure that changes location each year could help with both habitat and plant diversity over time. 

The burned patch of the patch-burn grazed prairie at Kankakee Sands. While the compass plant in this photo is blooming under grazing, other individuals (of compass plant, prairie dock, Canada milkvetch, and others) appear to be blooming less frequently than they did prior to the introduction of cattle. While this doesn't kill the plants over the short-term, it is a concern down the road, and the Kankakee Sands staff is considering strategies to mitigate those potential impacts.

A higher stocking rate would lead to more intense grazing of the dominant grasses such as big bluestem that are likely preventing existing forbs from becoming more abundant.  Currently many of the grass plants inside the most-recently burned patch are only being moderately grazed, and that can actually induce those plants to divert extra resources into rhizome production – leading them to expand their footprint (not the objective here).  More intense grazing on those grasses could create better opportunities for seed germination and seedling establishment around those plants, and would create even shorter vegetation structure, which might help attract upland sandpipers and as well as grasshopper sparrows. 

Regardless of stocking rate, the use of a grazing exclosure would help ensure a periodic break from grazing for plant species that otherwise be vulnerable to annual grazing – even in the unburned (and lightly grazed) portions of the prairie.  With a higher stocking rate, the exclosure would become even more important.  In addition to protecting plants from grazing, it would also protect fuel for the next year’s burn.  An exclosure roughly 1/4 or 1/3 of the size of the prairie would probably sufficient for protecting both plants and fuel, and would still leave cattle access to both burned and unburned portions of the prairie – something is important when promoting selective grazing. 

Even with those potential alterations to the current patch-burn grazing system, there are still plenty of unknowns about the long-term impacts of cattle grazing at Kankakee Sands.  It seems clear that grazing can create a shifting mosaic of habitat structure, but whether or not it can maintain the kind of plant diversity (and other diversity) desired by the Conservancy at this site is still an open question.

Discussing those kinds of questions while standing on the ground, however, is the best part of our Grassland Restoration Network workshops.  We don’t all agree on the best strategies, because we are all still experimenting with our own ideas on our own sites – and none of us feel like we have all the answers.  Being able to see for ourselves what various restoration and management treatment results look like helps us better compare those results to what we see on our own sites.  While we don’t have all the answers yet, we’re certainly moving much closer to them as a group than we would be individually.

14 thoughts on “Report from the 2011 Grassland Restoration Network – Part 2: Grassland Birds

  1. I am somewhat surprised that bird population isn’t connected to food availability and variety as well as habitat structure and size. Aren’t most grassland birds primarily insect eaters? I would think that would be a key in number and type of bird as the ready availability of food usually decides how many and where a species of any bird or animal lives, along with cover and other factors.

    • It’s a good question, Ernie. Birds are such generalists, though, that food availability is not an issue (as far as we understand). At least during the breeding season when there are loads of insects around. Because they don’t require a certain type or species of insect, grassland birds can find plenty of food in just about any kind of open, low-growing vegetation (prairie, smooth brome, alfalfa, etc.).

        • Actually, I just heard from an ornithologist friend that I may have overstated my response a little… Apparently there is some research showing food limitations in grassland birds, especially in lower diversity grasslands. Good news for those of us promoting biological diversity, I guess, but not great for birds living in brome fields…

  2. Good post Chris. A couple of things I wanted to comment on are:

    1) if an exclosure were added to a pasture and the actual number of animals in the pasture stayed the same, there would be a resultant increase in stocking rate because there are fewer graze-able acres as a result of the exclosure.

    2) Another idea that may address the desire to put more grazing pressure on the grasses would be to decrease the size of the burn patches. If the stocking rate of the whole pasture stays the same but the burn patch within the pasture decreases, the grazing pressure within the burn patch should increase. This may not be possible if a manager wants a 3-patch system where one-third of the pasture needs to be burned each year. But I hope patch burn grazing folks aren’t getting locked into the notion that a 3-patch system is the only way to go. Look where that type of thinking got us with prescribed fire – i.e., spring is the only time to burn.

    Having said all that, I like the idea of an exclosure(s) in a patch burn pasture because it would give a manager something different to look at and contrast with what is seen outside the exclosure. More forage for the mind in trying to figure out how fire, plants and animals interact.

  3. Pingback: Patch-Burn Grazing in Missouri Prairies | The Prairie Ecologist

  4. Our 130 acre restored prairie in MN is home to many Bobolinks in the summer. I was doing some hand weeding on the weekend of July 30 when I noticed a male Bobolink flying in slow circles with about 25 junveniles following in a flock. They were building up strength for the long flight south, a great sight it was!

  5. What grass and forb species do you recommend and what percentages for new prairie habitat development for Henslow sparrows in SE Indiana? What time of year is best to control burn for encouraging forb species in same area, zone 5 SE Indiana? Having a tough time getting forbs established in a fiver yr old predominantly Big Bluestem, Little Bluestem, Indiana grass project. Have been burning plots on 3 yr rotational basis in the spring. Planted forbs via no-till drill, overseeding, disking/broadcasting, winter frost/freeze, spring, and fall–trying every angle to no success for black eye susans, cone flowers, IL bundle, coreopsis. Have fair stands of goldenrod, and austrian pea coming into the wsg, but it’s primarily a very dense wsg stand. Thanks.

    • Hi Ann,

      Good question. I’m going to start by saying you should talk to someone more local than I am about techniques that work well there. I always try to get the most native plant diversity I can in our seedings because that benefits a large number of species. Henslow’s sparrows, though, probably don’t care so much about having hundreds of plant species as many other animals do. They seem to be tied more to habitat structure. I’ve seen lots of Henslow’s sparrows in very grassy CRP fields, for example. However, other people have said that forby prairies – and even brush prairies some places – can be even better. It probably depends on what else is around for choices!

      In terms of increasing forbs in warm-season grasses, it can be difficult. I’ve seen people have pretty good (temporary) results with disking/broadcasting around here. We’ve had decent luck with burning/seeding/grazing as well. Getting good seed-soil contact is really important to getting the plants started. But the key to long-term success seems to be finding ways to reduce the vigor of warm-season grasses periodically so they’re not always so dominant that few other species do well. Goldenrod is one species that seems to compete with those big grasses… Trying some kind of mid-season defoliation (mowing, burning, etc.) on a portion of the site each year can be one way to reduce grass vigor. Removing most of the leaves/stems when the grasses are growing strongly causes them to abandon large segments of root as well – so you open up both light availability and root space for new plants. I wrote a blog post on defoliation a while back – you can search my blog site for that post and see if that helps any.

      If you haven’t already, I’d sure talk to someone local – whether it’s someone from The Nature Conservancy, Pheasants Forever, or someone else that has experience with seedings in Indiana. If you want help finding someone, let me know and I’ll see what I can do.

      Good luck!

      • I have some experience with interseeding via no-till drill into dense wsg stands in north central Iowa. Anecdotally, I have observed that burning the spring after seeding is not advisable. I’m not a ecologist or conservationists by trade. So my observation and theories as to why this would occur should be considered with a degree of skepticism. Anyhow, I assume the spring fire –
        1) reinvigorates the wsg’s at a time when the forb seedlings are vulnerable,
        2) removes cover that would otherwise help to retain moisture, and
        3) possibly burns seed not sufficiently buried by the no-till drill.
        I wonder if Chris would agree or if he’s observed anything like this?

        • Interesting. I actually don’t have any experience with a no-till drill planting method. What time of year are you planting? Are you talking about burning in the spring of the first growing season after seeding? In other words, you’d seed in march and burn in April? Or seed in November and burn in March? Or are you talking about burning the NEXT season (plant in March 2011 and burn in March 2012)?

          I’ve not seen any problems with new cropfield seedings when we’ve burned right before the second growing season starts. In fact, it seems to help with early spring forbs.

          Response to fires between grasses and forbs are a mystery to me because the results people see seems to vary a lot from site to site. Some places see great plant diversity, including abundant forbs, with annual fire. Others see a quick move to grass dominance under the same kind of fire regime. Too many variables to understand at this point.

          • In my case, we mowed a ~25 year old wsg stand and no-till drilled through the thatch in the fall. The following spring, we burned ~1/4 of the seeded area. Of course, since it was mowed the fall before, the fire was low to the ground but relatively long lasting since the fuel was concentrated at ground level. In the unburned area, numerous species established (cream gentian, ohio spiderwort, compass flower, white baptisia, blazing star etc.). In the burned area, not nearly as many forbes established. After one growing season, the entire seeded area was burned.

          • Very interesting. I’ve wondered about, but have no data on whether or not fire has a detrimental impact after seeding like that. Some species germinate better after fire, but I wouldn’t be surprised if others are damaged by fire. Hard to say. When you figure it out, let me know!!

  6. Pingback: The Annual Grassland Restoration Network Workshop – Coming to A Prairie Near You (If You’re Near Columbia, Missouri) | The Prairie Ecologist


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