Tag Archives: grassland birds

Grassland Birds in Prairie Restorations: Response to a Research Paper

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A “Restoration Note” published in the most recent issue of the journal Ecological Restoration (March/June 2011) caught my attention last week.  I was initially interested because some of our sites had been part of the study but I hadn’t seen or heard about any of the results.  However, after reading the note (a short research article) I found myself musing yet again about the kinds of expectations people have for prairie restorations.  In this case, the authors were comparing bird communities in restored prairie to those in relatively degraded remnants with the idea that identical bird communities would equate to a measure of success for the restored prairies – something I strongly disagree with.  I apologize for not being able to provide you with anything more than the citation below and some paraphrasing of the article.  I requested permission from Ecological Restoration to post a PDF of the Restoration Note itself, but was turned down, and there is no abstract because of the short length of the article itself.  I guess if you want to read the whole article and don’t have a subscription to the journal, you’ll have to either go to a library to find it or pay their fee ($17!!) to read it online.

Nevertheless, here’s the citation for the article:

Ramírez-Yáñez, L. E., Chávez-Ramírez, F., Kim, D., Heredia-Pineda, F.  2011.  Grassland Bird Nesting on Restored and Remnant Prairies in South Central Nebraska.  Ecological Restoration 29:1-2, pgs 8-10.

In the study, the authors measured grassland bird abundance and vegetation structure/composition in six restored prairies (former cropland) and six remnant prairies (relatively degraded) along the Central Platte River valley in Nebraska.  The restored prairies ranged from 5-15 years in age, but the authors didn’t specify how many were in the younger vs. older stages.  Of the restored prairies on our property that I think were used in the study, two were seeded in 2002 and the other in 2001 (the paper isn’t clear about how many years of data were used for the analysis, or what years they were).  The researchers looked mostly at three bird species (bobolinks, grasshopper sparrows, and dickcissels) and located nests for each.

Grasshopper sparrows are nearly ubiquitous - often in high densities - in grazed pastures along the Platte River in Nebraska

From their vegetation data collection, the researchers found that the plant species richness of the remnant and restored prairies was very similar.  However, remnant prairies had more cover of low-growing grass species such as Scribner’s panicum and tall and sand dropseeds.  Restored prairies had more tall forbs such as sunflowers and goldenrods.  The average height of the vegetation was quite a bit taller in the restored prairies than the remnant prairies (average of 96 cm in restorations and 59cm in remnants).

The researchers found 242 grassland bird nests in remnant prairies and 264 in restored prairies.  There were significant differences between restored and remnant prairies in the abundance of nests of the three species they focused on.  Bobolinks and grasshopper sparrows had more than twice as many nests in remnant prairies than in restored prairies.  Dickcissels, on the other hand, had three times as many nests in restored sites as in remnants.

DIckcissels prefer tall forby vegetation structure like that found in young restored prairies.

Based on the vegetation data collected, the results of the bird data fits well with what would generally be expected – and what I observe in our sites.  Dickcissels tend to like sites with taller vegetation, especially when abundant tall forbs are present.  In contrast, grasshopper sparrows and bobolinks are most abundant in pastures and hayed prairies, respectively, where vegetation is kept short, and regular cropping of grasses favors those species with shorter stature.  Up to this point, as I read the paper, everything the authors were reporting fit with what I see for bird use in our Platte River prairies.  What threw me for a loop was the final paragraph of the article, in which the authors presented their interpretation of their data and the conclusions they had drawn from it.  The following is that last paragraph:

“Our preliminary data suggest that these restorations, at this point in time, are not creating the nesting habitat required or preferred by birds in more natural grasslands.  Most restoration practices focus on vegetation reestablishment and cover (Martin et al. 2005), which represent the restoration of primary production but do not ensure the recuperation of essential habitat components needed by native fauna (Whisenant 2005). Our preliminary results have promoted a change in our philosophy to include wildlife habitat requirements at the planning stage of restorations.”

There are three points I’d like to make about that paragraph and the conclusions drawn by the authors of the paper.  The first is something I’ve dealt with in a previous post.  The authors are assuming that the point of prairie restoration is to replicate existing prairies – at least, in this case, in terms of the vegetation structure and relative composition of the plant and bird communities.  Even in cases where remnant prairies are very high quality, I feel strongly that trying to replicate them through prairie restoration is not only unwise, it’s a strategy that is doomed to fail.  The management history, soil conditions, and many other factors are very different in a remnant prairie than they will be in a restored prairie.  Moreover, along the Platte River, the remnant prairies are almost all degraded – many significantly so – by overgrazing, repetitive haying, and/or broadcast herbicide application.  As a result most are missing many important prairie plant species and are largely dominated by grasses (including invasive grasses such as smooth brome and Kentucky bluegrass).  I think that most botanists would cringe at the idea of trying to replicate those prairie plant communities because of their degraded state.  Our restoration work, in fact, has focused not on replicating remnant prairies, but on enlarging and re-connecting them to each other by restoring cropland in between them with restored prairies planted with seed mixtures that maximize the diversity of locally-native plant species.  Those seedings, as they mature, are managed to maintain their biological diversity (including birds) – not to make them resemble the remnant native prairies adjacent to them.  In fact, we consider it to be a measure of success that the restored prairies contain many plant species no longer found in most nearby remnants.

The second point relates to the first, but deals specifically with the bird communities in the restored and remnant prairies.  Grasshopper sparrows and bobolinks are among the most abundant bird species in the landscape surrounding our restored prairies, and dickcissels (and other species that prefer tall forby vegetation structure) are relatively rare.  To me, creating restored prairies that complement the bird communities in the surrounding landscapes by providing habitat for dickcissels seems like a savvy conservation strategy.  If restored prairies favored the same bird species as the remnants, very little would be gained in the landscape since the amount of restored prairie is very small compared to the amount of remnant prairie.  We would simply be adding a few more grasshopper sparrows and bobolinks to the landscape – and we’d still be low on dickcissels.

Bobolinks are frequently found in hayed prairies along the central Platte River, as well as in light-moderately grazed prairies. (This one is sitting in a restored prairie)

The third point is that the authors are comparing grasslands (restorations to remnants) that differ significantly in both current and historical management.  The remnant prairies have long histories of either season-long intensive grazing and/or annual haying that has strongly influenced their plant species compositions.  Even though the remnants in the study are now primarily managed with fire and grazing, the plant community composition in those prairies is much more a product of historic than recent management.  In contrast to the remnant prairies, most of the restored prairies in the study have had mostly periodic dormant-season fire management that has encouraged dominance by the tall grasses and forbs that make up a large part of their plant community.  Plant species (such as panic grasses, dropseeds, and exotic cool-season grasses) that thrive in repetitively grazed or hayed prairies are not dominant.  Some of the restored prairies in the study are sufficiently established that they are now being grazed somewhat similarly to the remnant prairies – though generally at lighter stocking rates – but that management has not been going on long enough to greatly influence plant species composition.  It is no surprise, therefore, that the species composition and vegetation structure of the remnant and restored prairies are different from each other.  That difference reflects not a failure of the restoration process, but is rather a product of the difference in the length and type of management the sites have received.

To build a little further on the last point, IF the goal of the prairie restoration process along the Platte was to create prairies with plant species composition and vegetation structure similar to that of remnants, success would depend much more on management strategy than restoration planning and design.  Yes, alterations in the initial seed mixture to favor panic grasses, dropseeds (and invasives?) could give those species a greater relative abundance more quickly during the establishment of the restored prairie.  However, management is going to drive that establishment process much more than seeding design.  With periodic dormant-season fire, those species will not thrive, and warm-season native grasses and large forbs will still dominate – even if they start with lower abundances.  In contrast, relatively frequent and intensive grazing (or annual haying) would push the plant community toward high abundances of those lower-growing grasses (and probably fewer late-season tall forbs).  If you started with two young restored prairies – one with lots of low-growing grasses and few tall grasses and forbs, and one with the opposite composition – those plant communities could be pushed in opposite directions through management until each became nearly identical to the other.  In other words, if the authors of this paper want to favor grasshopper sparrows and bobolinks in future prairie restoration efforts, they could alter their restoration design to increase the abundance of low-growing grasses, etc., but they would be much better served spending their time on plans for an appropriate management regime instead.

To be clear, I don’t question or disagree with the data collected by the researchers on this project, I simply disagree with the conclusions and implications they drew from their results.  First, I’m not sure why they are disappointed to see an abundance of dickcissels in restored prairie, given their relative scarcity in the surrounding landscape.  More importantly, I have a much different set of objectives for restored prairies than they do.  Mine are related to contributions of restored prairie to landscape function and population/species viability, rather than to an attempt to replicate existing remnant prairies.

However, this kind of discussion over what prairie restoration should aim to accomplish (and what it CAN accomplish) is very productive.  The publication of articles that evaluate restored prairies – even those with a different perspective than mine! – is extremely valuable, and stimulates conversations that should move us significantly forward in our attempt to conserve and restore grassland ecosystems.  I would appreciate hearing from you about your perspectives on this and other similar topics.

Why Grassland Birds are Poor Indicators of Prairie Quality

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I presented this argument to a Nebraska symposium on grassland birds in 2008 and managed to escape relatively unscathed.  Now I’m testing my luck with a wider audience.  At least no one can throw things at me through the computer…

Let me start by saying that I’m a big fan of birds.  I really enjoyed working on my graduate research, which focused on grassland birds and their vulnerability to prairie fragmentation.  I also think birds are generally pretty and interesting. However, the truth is that prairie birds make up only a tiny percentage of the species in prairies (most of which are invertebrates, followed by plants).

Grassland birds make up a tiny percentage of the species living in a prairie - the vast majority of which are invertebrates and plants.

However, grassland birds are often held up as indicators of whether or not a prairie – or a prairie landscape – is “healthy” or “high quality.”  A common refrain in prairie conservation goes something like this; “If we have our full complement of grassland birds in this prairie and/or landscape, it’s a good bet that all the other species are also doing well.”  Unfortunately, while prairie birds are relatively easy to study and monitor, they may not do a good job of reflecting how the rest of the prairie is doing.  Let’s look at some of the most important attributes of prairies and some of their major threats – and consider how well birds correlate with them.

Species Needs – Survival, Reproduction, and Dispersal.

First and foremost, species have to survive and reproduce in order to persist in a prairie.  This applies to every species, from large vertebrates to tiny invertebrates and the entire suite of plants.  It’s important for us to know that grassland birds are surviving and reproducing, but can they tell us whether other species are doing the same?  You could argue that because they eat insects, grassland birds could have an impact on the survival of some insect species.  That’s true to a point, but grassland birds are generalist feeders – they tend to eat whatever insects are easiest to catch at any particular time – so while the abundance of grassland birds might impact the overall abundance of insects, you can’t really tie the presence of a particular grassland bird species to the survival of a particular insect species (or vice versa).  In other words, the plight of a rare leaf hopper or butterfly species is unlikely to be correlated with grassland birds.  Nor are grassland birds good predictors of plant species survival – the presence of meadowlarks or Henslow’s sparrows tell us nothing about whether or not compass plant or leadplant is thriving.  Grassland birds require certain habitat structure types (short vegetation, tall/dense vegetation, etc.) but they don’t much care whether that vegetation consists of smooth brome and sweet clover or a large diversity of native plants.

Henslow's sparrows are a bird of conservation concern and their presence in a prairie can be seen as a conservation success. However, although they tend to require fairly large prairies, and can indicate the presence of certain vegetation structure types, they don't indicate whether or not a prairie has a diverse plant or insect community.

In addition to basic survival, animal and plant species need to be able to move around the landscape in order to recolonize places where they have disappeared, and to maintain genetic interaction between populations (important for genetic diversity).  In landscapes where prairies exist as isolated remnants, moving between prairies becomes very difficult.  Corridors of prairie vegetation between prairies become important in those landscapes, and prairies near each other provide better opportunities for interaction within species than do more isolated prairies.  Because most grassland birds fly south at the end of each season and return the next year, (and the ones that don’t can still fly long distances between prairies) they don’t rely on those physical connections between prairies like most other animals and plants do.  Since grassland birds are pretty unique in terms of long-distance flying ability, they are a poor indicator of conditions that affect less mobile species.

Ecological Services and Ecological Function – Pollination, Seed Dispersal, etc.

Apart from the needs of individual species, prairies rely on certain processes to keep everything humming along.  Pollination and seed dispersal are two good examples.  Both affect the viability of prairie plant species, and neither has much to do with grassland birds.  Pollination primarily relies on plant diversity and bees – the most important pollinator group in prairies – and both plant diversity and bees are pretty disconnected from grassland birds.  We don’t know much about the role of prairie birds as seed dispersers, but it’s a good bet that they do very little seed dispersal during the summer when they’re primarily eating insects.  The role of migrating grassland birds as seed dispersers would be an interesting thing to study – but our use of grassland birds as indicators of prairie quality is always based on their presence during the breeding season.  If you were going to measure whether or not pollination and seed dispersal were functioning adequately, you’d likely evaluate the diversity of plants, the abundance of bees, and some of the potential obstacles to seed dispersal (tree lines, isolation of prairies, etc.), but I don’t think measuring grassland birds would tell you much.

Resilience – Redundancy and the Ability to Withstand Stresses and Invasive Species.

One way to think about the resilience of a prairie is as a measure of how well the prairie can bounce back from stresses.  For example, species diversity adds resilience to a prairie because when many species are present – especially when they overlap in the roles they play – the loss of an individual species can be a relatively minor blow.  If there are dozens of bee species pollinating flowers in a prairie, a disease that wipes out one or two species will probably not have a huge impact on seed production.  A diversity of plant species can also help to dampen the impacts of an event such as a severe drought or intensive grazing that temporarily weakens the vigor and growth of dominant plant species.  When there are lots of plant species present, the weakening of some leads to increased growth and abundance of others.  This helps maintain a stable supply of food for herbivores, and also helps prevent encroachment by invasive species that might otherwise take advantage of the weakened plant community.

Grassland birds may help bolster the resilience of a prairie in some ways.  They might, for example, help suppress an outbreak of grasshoppers by focusing their feeding on that easy-to-find prey species, and thus limit its abundance.  However, as discussed earlier, they don’t have much to do with pollination, nor would they help provide food for herbivores during a drought.

If you want pollination you need bees, not birds.

Threats to Prairies – Habitat Fragmentation, Invasive Species, Broadcast Herbicide Use, and Chronic Overgrazing.

One of the best arguments for grassland birds as an indicator of prairie health is that they are vulnerable to the loss and fragmentation of grassland habitat.  This is true.  A diverse and successfully reproducing community of grassland birds requires relatively large and unfragmented grassland.  In addition, because some grassland breeding birds need short vegetation and others need tall/dense vegetation, a diversity of birds can indicate a diversity of available habitat structure  – and that’s important to many other wildlife species as well.  Greater Prairie Chickens are often promoted as particularly good indicators because they are a single species that needs both large grasslands and a diversity of habitat structure.

However, there are a couple of other things to consider.  First, while some grassland bird species need large prairies, we don’t really know whether the minimum area required by grassland bird species is larger or smaller than that required by plant or insect species.  We know that many prairie plant species have survived for a very long time in tiny isolated prairies.  But because individual plants of many species can live almost indefinitely, due to their ability to generate new plants through rhizomes and other asexual means, the populations of plants in those tiny prairies could be in a death spiral due to the lack of genetic interaction with other populations.  You could make the argument that plants need much larger prairies than birds (thousands of acres, perhaps?) in order to maintain genetic fitness.  We simply don’t know.  And we know even less about the prairie size needs of insects.

Second, while grassland birds do require fairly large grasslands, most don’t actually require PRAIRIES.  Prairie chickens and many other grassland bird species have benefitted greatly from Conservation Reserve Program (CRP) fields that have added large numbers of acres of switchgrass, brome, and low-diversity grasslands to agricultural landscapes.  However, those same CRP fields have done very little for native wildflower populations or pollinator insects (or other insects that rely on diverse communities of native plants) so the increase in grassland birds in landscapes with CRP doesn’t really tell us much about the health of most other prairie species.

This smooth brome-dominated grassland is of very little to most prairie species, but would provide relatively good habitat for some grassland bird species (except for the trees in the background).

Because grassland birds can live comfortably in grasslands made up of a few native grasses, or even non-native grasses, they are poor indicators of the impacts of most invasive species – a major threat to prairies.  Similarly, broadcast herbicide use that greatly reduces the number of plant species in a prairie has little impact on the grassland birds nesting there.  Finally, a prairie that is being overgrazed would certainly have different bird species than one that is not being grazed at all, but a prairie that was chronically overgrazed for decades – and then managed well again – would have a pretty low number of prairie wildflower species but a very nice-looking grassland bird community.

One threat that grassland birds can be an excellent indicator for is tree encroachment on prairies.  Most grassland birds avoid nesting anywhere near even a solitary tree, let alone a grove of them, so a prairie with few birds could indicate a tree problem.  On the other hand, it’s pretty hard to miss a bunch of trees growing in a prairie…

Summary

Here’s the real point.  Grassland birds are an important component of prairies.  A prairie without all of its appropriate prairie bird species, or in which those species are not successfully raising broods, is missing something valuable.  Improving grassland bird success in prairie landscapes is an important and worthwhile objective.  At the same time, however, a prairie that has a full complement of successful grassland bird species doesn’t necessarily have diverse plant and insect communities, functioning ecological processes, or a low risk of invasive species or other threats.  In other words, grassland birds are an important component of high quality prairies, but their presence and/or success doesn’t necessarily mean a prairie is high quality.

Now that I’ve spent 1,500 words bashing prairie birds (I really do like birds…) the relevant question is, “What SHOULD we use as indicators of prairie conservation success?”  I wish I had a simple answer.  Part of the answer, of course, depends on how you visualize prairie quality (see my earlier post on this subject) because evaluation needs to reflect objectives.  But if our vision of a high-quality prairie includes species diversity, habitat heterogeneity, and other complexities, our evaluation methods will have to be complex as well.  Figuring out how to “take the pulse” of prairies may be the most important conservation challenge we face, because without that information we can’t design effective conservation strategies.

While we still have a lot to learn about how to take that pulse, it’s clear that we’ll have to do more than just count birds…