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

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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.

Neighborhood Watch

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When making management plans for a prairie, it’s a good idea to look over the fence to see what the neighbors are doing.  It’s important to think about how your prairie fits into the landscape, and even more important to think about what you can do to complement the prairie habitats/conditions around you.  If your prairie is the only one around for miles, you’ve got bigger problems than this post will be able to address (I’ll hit that topic in the future, though).   If there ARE other prairies – or at least grasslands – nearby, continue reading…

There are many ways to make your prairie provide a complement to the ecological contributions of others in the landscape.  Rather than trying to cover all of them, here are three examples:

Grassland Birds

Though focused on birds, this section really applies to small mammals, insects, and any other animals that rely on a particular kind of habitat structure (or multiple kinds) for survival as well.  Many times, the majority of prairies/grasslands in a neighborhood are managed so that the vegetation structure in all of them looks pretty much the same.  In some cases, the landscape may be full of grazed pastures – all with relatively short grass.  This might provide excellent habitat for species like grasshopper sparrows and upland sandpipers (depending upon how large each grassland patch is) but doesn’t do much for dickcissels and Henslow’s sparrows.  On the flip side, other landscapes have an abundance of Conservation Reserve Program (CRP) or other grasslands that are rarely burned or grazed and consist mainly of tall thatchy vegetation.  In either case, thinking about how your prairie could provide some vegetation structure that is rare or absent from the surrounding landscape can really benefit species requiring that habitat type.

Dickcissels are large sparrows that prefer tall weedy habitats, and aren't likely to be found in prairie landscapes with only short vegetation structure.

A somewhat more complicated scenario applies to a few species that require different habitat types for each season.  Prairie chickens, northern bobwhites, and ring-necked pheasants, for example, need to be able to move back and forth between nesting and brood-rearing habitat without having to travel very far.  Nesting cover (which may double as winter cover) typically consists of relatively dense vegetation that can conceal a nest and the female sitting on it.  However, newly-hatched chicks have to be able to travel through that cover to nearby feeding areas, so it can’t be so dense that those chicks can’t make their way around in it.  Ideal brood-rearing cover has areas of relatively tall wildflowers or weedy vegetation without dense grass at the ground level – this allows adults and chicks to easily move around and chase insects, but also provides overhead protection from predators.  The interspersion of nesting and brood-rearing cover across the landscape is a key factor in the annual survival of these species.  If the prairie adjacent to yours is providing excellent habitat for one of those two life stages, providing the other in your prairie might fill a critical habitat need.

Obviously, there are any number of other vertebrates and invertebrates that have habitat structure requirements.  Even without knowing what those requirements are, you can help provide for them by simply trying to manage your prairie to fill in gaps in the landscape – or to improve the interspersion of those habitat types in the neighborhood.  Sometimes it’s as simple as ensuring that the vegetation structure in your prairie contrasts with what’s around you.  In other cases, timing of management can be important.  If your neighbor cuts hay in mid-July, for example, there will likely be quite a few newly-fledged grassland birds, small mammals, and other animals looking for refuge.  If you plan to hay your prairie as well, delaying for a month or so can give those species at least a temporary reprieve – and in the case of many birds, may give them enough habitat to last them until migration time.  Leaving a portion of your prairie unhayed, of course, could also be valuable.  Another example related to timing could be to try to stagger the timing of your prescribed fires with your neighbor so that you’re not both burning your prairie in the same year (or season). 

Bees

Bees are one of the most important groups of insects in prairies because of their effectiveness as pollinators.  The two primary needs of bees are nesting habitat and food.  Bees have varying requirements for nesting habitats, but many either need bare ground for burrows or old woody debris.  Looking around to see whether neighboring properties provide that kind of habitat could help you think about what to do on your own land. 

A native bee on a prairie wild rose.

In terms of food, it’s important for bees and other pollinators to have consistent sources of nectar and pollen throughout the season.  It can be valuable – and instructive – to keep track of when each flower species blooms in your prairie and that of surrounding prairies (including roadsides and gardens).  Imagine yourself as a native solitary bee with a feeding radius of about ¼ mile around its nest.  Could you find something to eat on every day of the growing season?  If there are gaps during the season when there’s really nothing blooming in the neighborhood – or only a few flowering species blooming – that could identify an important gap to address.  Often, early season flowers are hard to come by, but there may also be mid-season gaps due to management practices (haying, burning, grazing) or simply because there are no/few flower species that happen to bloom at that time.

Providing for pollen and nectar resources in your neighborhood could be as easy as ensuring your prescribed fires, haying, and/or grazing activities aren’t happening simultaneously with that of your neighbors.  In other cases, it might be that you could manage in a way that encourages flowering plants during a time period when not much is blooming elsewhere nearby.  Regardless, it’s an interesting and important aspect of habitat to pay attention to.

Plants

In landscapes where land management practices are very similar across all land parcels, there are likely to be plant species that become rare because they never get favorable growing conditions.  Identifying those species and altering your management to accommodate them – at least periodically – can be an important strategy.  If most of the neighbors are burning every spring, skipping a year now and then on your land might help some of those spring-growing plants to survive.  In landscapes where grazing is commonplace, most ranchers/farmers tend to employ a fairly standard – and repetitive – grazing system.  Identifying the impacts to plant species (good and bad) of the grazing systems around you can help you facilitate success for those species in your prairie.  On the other end of the spectrum, if no grazing is occurring in the surrounding landscape, there may be species that thrive under grazing that could benefit from some grazing on your own land.  Whatever the local situation, recognizing the impacts of the management occurring around you on plant species can help you design management strategies that can prop up populations of plants that are otherwise struggling.

Caution!

It’s important to remember that the above examples and suggestions are just that – and may not apply to your situation.  Even more importantly, it’s not a good idea to implement a repetitive management system on your own prairie to contrast with the repetitive management system(s) of your neighbors.  (In other words, don’t manage exclusively for dickcissels just because the neighbors are managing exclusively for grasshopper sparrows…)

Repetitive management that decreases the ecological resilience of your prairie can lead to a weakened prairie community that can be more vulnerable to invasive species and other threats.  There’s no need to sacrifice the integrity of your prairie for the good of the neighborhood.  Instead, think about trying to maintain the highest plant and animal diversity you can on your own prairie – while also watching for opportunities to contribute rare or missing habitat components to the surrounding landscape.  The latter is an important, but secondary, consideration.

The prairie looks very much the same on both sides of this fenceline.

The ideal situation is one in which adjacent neighbors (or an entire neighborhood) coordinate their management so that each prairie is well-managed, but so that management actions aren’t synchronized across the landscape.  Staggering the timing of prescribed fires, haying, and grazing between neighbors to ensure that everyone isn’t doing the same thing during the same season can be very important. 

(Communication between neighbors about management can have additional benefits, of course, besides simply coordinating the timing or other aspects of management.  For example, talking about the success or failure of invasive species control efforts or observed trends in plant or animal responses due to particular management strategies can help everyone improve their own properties. )

The Upshot

Regardless of the size or location of your prairie, it’s valuable to look around the neighborhood as you plan your management each year.  I’ve provided a few examples of how one prairie can fill gaps left by the management of nearby prairies, but there are many more – each landscape is unique.  The key is simply to be thoughtful about your prairie management, and to remember that wildlife and plant populations don’t stop at the edges of your property.