Reassessing the Raytharn Farm Grasslands

Between a pasture and a crop circle

Since 1997, the Pennypack Trust has been working diligently to create habitat for meadow-nesting birds which, as a group, are the most endangered suite of birds on the East Coast because of habitat loss.  Our strategy has been to establish native, warm-season grasses on the 160-acre Raytharn Farm we purchased that year.  Now nearly two decades into the project, we have a fairly respectable stand of native "prairie" grasses cloaking the land.  The grasses are beautiful (especially this time of year), resilient, and very popular with our visitors - but not with the birds we are trying to attract.  Eastern Meadowlarks, Bobolinks, and several species of sparrows stop in the grasslands during migration, but they never stay to breed.  What's wrong?  Didn't we do everything right?

Well, it turns out we didn't do everything right.  Grassland managers all along the East Coast have come to realize that the birds are seeking diversity - diversity in height and diversity in plant composition.  To the birds, our grasslands are too dense, too tall, and too monotonous, and they don't provide food (i.e., insects) in sufficient quantities for nestlings.

So, you might recommend that we diversify the grasslands, and you'd be right.  However, we also have a terrible problem with invasive plants.  The grasses can be treated with special herbicides that kill all invasive plants except the grasses, but there's no such "magic bullet" for diverse combinations of plants.  Once invasive plants colonize a mixed-vegetation meadow, control becomes much more time consuming and costly because the invasive plants have to be removed "surgically" without disturbing the desirable plants.  We've resisted trying to diversify our grasslands for that reason.

But, we've finally come to the realization that (1) we're not going to attract meadow-nesting birds if we don't do something different, and (2) if we can't attract meadow-nesting birds, why have the grasses at all because our landscape really wants to be a forest and we have to fight Mother Nature (i.e., natural succession) to keep it in grassland.

Fortuitously, I recently ran into Roger Latham, a respected field ecologist.  Roger and I are good friends, and he has visited Pennypack to consult on several occasions.  He also served on the board of directors of the Natural Lands Trust (NLT), which has preserves all over southeastern Pennsylvania and southern New Jersey.  He told me that NLT's Gwynedd Wildlife Preserve near Ambler had had Eastern Meadowlarks nesting in its native grasslands this summer, and he suggested that I talk to Gwynedd's land manager for some guidance.  So, I rounded-up Pennypack's senior stewardship staff for a field trip and we paid a visit to Gwynedd on October 30.  

Edge of the "crop circle" (darker foreground), native grassland (tawny center) and pasture (green, far left)

Tom, Gwynedd 's land manager had successfully created native grasslands like we had, but had also failed to attract meadow-nesting birds.  Then, he decided to create "crop circles" - round meadows within the grasslands that he seeded with a mixture of 16 different species of low-growing flowering plants (i.e., wildflowers).  Three years ago, he established about 10 such circles ranging in size from 0.25-acre to over 4 acres.  And, this summer, Eastern Meadowlarks nested in his preserve - not in the crop circles (and not in the native grasses), but in a pasture composed of non-native grasses immediately adjacent to the largest crop circle.  

Diverse crop circle vegetation (foreground)

Tom watched the meadowlarks build nests in the pasture (which is just as monotonous a monoculture as the native grasslands, but lower in height).  Then he watched the adult birds fly into the crop circle to catch insects that were using the wildflowers.  Success!

Crop circle (foreground), native grasslands (mid-ground), and woodland (background)

Tom's crop circles get colonized by the same invasive plant species with which we have to contend, but he told us that he is able to control the invasives before they become problematic with a combination of mowing before the invaders set seed, spot application of herbicide, and the judicious use of a string trimmer.  He's got a smaller land stewardship staff than Pennypack does, so Pennypack's staff should be able to do as well.

Crop circle (right) and native grassland (left)

Pennypack's staff drew-up plans for the Raytharn Farm grassland modifications in the car on the way back to Pennypack.  Stay tuned; it may be a year or two before we're successful, but at least we now have a plan!

 

Autumn color in the Gwynedd grasslands

 Submitted by David Robertson

 Executive Director

Sora Out of Water

Sora (Porzana carolina) [Image from an Internet source]

This morning, two of Pennypack's best birders and nature photographers, Harris Brown and Fran Ventura, stopped in the office after a morning photo shoot to report that they had found and rescued a Sora (Porzana carolina) on a trail through the tall native grasslands on Raytharn Farm.  The Sora (a type of rail) was alive (though clearly injured or sick); Harris and Fran planned to take it to the Aark wildlife rehabilitation facility in Chalfont to see if it could be saved.

Two years ago, Pennypack birder Michael Grubb found a Sora on another of the Raytharn Farm grassland trails, but that bird was dead. 

I have no idea why a fairly uncommon bird almost always associated with marshes would be found high and dry in the prairie-like grasslands we have established in parts of the Pennypack Preserve.  Nor do I have any idea why these birds are in bad shape.  It's great that they're here, but not if the preserve is acting as a "sink" in which the birds fall victim to predators or disease.

 

Posted by David Robertson

Executive Director 

Frosty November Morn

 

I awoke on Saturday morning (November 9) to the beautifully frosted native grasslands on Raytharn Farm.  I did my best to capture the crispness before the rapidly rising sun dispelled the magic.

Weedy, non-native foxtail (Setaria spp.) in front of tawny Indian-grass (Sorghastrum nutans)

Rimed thistle rosette and oak leaf

Submitted by David Robertson
Executive Director

Of Birds and Men

Pennypack Executive Director David Robertson (left) with Pennsylvania Game Commission grassland bird expert Dan Mummert

For the last thirteen years, Pennypack's land stewardship staff has been working to convert the 160-acre Raytharn Farm into native warm-season grasslands.  Our goal has been to create habitat that will support breeding populations of "grassland obligate" birds - birds that nest in grasslands and in no other habitat.  Good examples in our area include Bobolinks; Eastern Meadowlarks; Savannah, Grasshopper and Vesper Sparrows; and Upland Sandpipers (the last one being, admittedly, a real long shot).

When we bought the property in 1997, the land was used to grow non-native cool-season grasses that were harvested for hay.  We started small with our conversion; each year, we would herbicide a 10- or 25-acre patch of the pasture grasses, and then reseed the area with native grass seed.  In 2008 we finally finished the conversion by reseeding the final 50-acre patch.

The grasses have performed well, and our farm now looks much like a tallgrass prairie in the Midwest.  Though the grassland conversion has been very successful, none of the grassland obligate birds has chosen to nest in the fields yet (with the notable exception of one very rare species that occurs in only a few very scattered locations in Pennsylvania - our resounding success to date).  We routinely observe Bobolinks and Eastern Meadowlarks stopping for a few days in the fields during spring and autumn migration, and each year we hope they'll linger to raise a brood, but inevitably they move on.

We have our suspicions about why they don't nest here.  The largest contributor to their decision may be that the fields are just too dense with grasses, and they can't find suitable small open patches in which to build their nests.  We know this is an issue, but there's a good reason why there aren't many openings in the fields:  we have an absolutely horrendous problem with non-native invasive plants. Any openings in the dense grass cover are quickly colonized by invasive plants, which then begin to spread and take over the grasslands.  So, we use herbicides to control the broad-leaved invasive weeds, which reduces competition for the grasses, and the grasses grow in to fill the openings.  Result: few nesting sites.

Grasslands with desirable diversity

Furthermore, the grasslands are not diverse and don't contain many meadow plants that would attract insects and pollinators on which the birds could feed.  Again, most of the good native wildflowers that we could seed into the grasslands would be killed by the broad-leaf herbicides we use to control the pernicious invasive plants, so we can't create a diverse meadow with a mixture of grasses and broad-leaved native wildflowers.  A 60:40 grass:wildflower mix is ideal; we probably have 90:10.      

Oh, and another thing.  The Pennypack Preserve is in the middle of the suburbs.  We're largely surrounded by houses, roads, and businesses.  So our grassland is an island in a suburban sea, and it simply may not appeal to these grassland obligates that are used to wide open expanses of grassland in an agricultural matrix.

So, long and short, we may never be successful in getting grassland obligate birds to nest in our grasslands, but it doesn't stop us from trying.  One of our premier birders, Harris Brown, called the Pennsylvania Game Commission when he learned that the commission employs a consulting grassland expert who would be willing to visit and share his knowledge and recommendations with us.  The expert, Dan Mummert, visited the Pennypack Preserve on Tuesday, August 27 and Harris and the staff escorted Dan on a tour through the fields.

From left:  Staff members Brad Nyholm, Christopher Dartley, and David Robertson; volunteer Harris Brown; and Dan Mummert

Dan commended us for our success in establishing our grasslands in light of the nearly overwhelming pressure of invasive plants, and considering that we cannot use the two tools best suited to managing grasslands: prescribed burning and disking.  (We can't burn because of air pollution regulations and because the local fire marshals are terrified that we'll burn down houses on our periphery.  We can't disk the fields because we'd open up bare ground that would be colonized by invasives.)  

He did note that some of the grasslands contained wildflowers and that not all of the fields were grass monocultures; he encouraged us to try to create similar diversity in fields that were dominated solely by grasses.  He also recommended that we remove trees that had become established in fence-rows; the trees serve as perches from which raptors can survey the fields for prey, and the trees interrupt the "flow" of the broad grassy expanses the birds are seeking.  And last, but not least, he recommended that we consider closing some of our trails through the center of the grasslands during the birds' breeding season (May to mid-July) to limit disturbance by human activity.

None of these recommendations was new.  We'd had other wildlife biologists make similar suggestions in the past, but it's good to hear that everyone is "singing from the same hymnal."  We'll have to give all of these suggestions some thought since we have to weigh aesthetics, land management, and public use in the preserve.

Submitted by
David Robertson, Executive Director