Garlic Mustard Setup

by Carl Strang

One of my ongoing studies in recent years has been a pursuit of best practices for manual removal of garlic mustard, an invasive biennial that is one of the banes of terrestrial plant community restoration. Following an early study by researchers in downstate Illinois, I have confirmed that while uprooting of plants is effective, and is the most effective method early in the season, clipping the tops at ground level works equally well late in the season, and none of these practices increase garlic mustard seed bank germination as far as I can tell. (If you want to review my study to this point, go to the left frame of this blog and do a search on “garlic mustard.” You will scroll through all the posts in which the plant is mentioned. The first one in this study is dated March 20, 2009).

Individual hand-clipping of plants is inefficient, however, and so this year I wanted to test how well mass cutting of late-season garlic mustard plants replicates the earlier results. The problem that arose was my back strain, which made me leery of swinging the grass whip that was my chosen tool. The pressure was on, however, as this year’s early season had the plants developing apace, and so as they were showing their final flowers I decided to suck it in and give it a try. I wasn’t able to crouch down and mark out study plots as I have done in the past, and I wasn’t willing to do a lot of plots, so I settled for cutting and raking two adjacent areas dominated by dense garlic mustard plants. One of those areas I cut close enough to ground level to eliminate all the leaf-bearing parts of stems.

These photos are from a couple weeks after the cutting. The leaves here are those of creeping Charlie. At this point there is no recovery of garlic mustard evident.

It didn’t take a lot of effort to remove a volume of plants with this close-cut variant. In the other plot I cut the plants at around 10 inches above ground level, a height selected to match the practice I have seen used by some restoration workers.

Here you see the cut stems.

By the time I got around to taking the photos, adjacent garlic mustard plants had completed flowering and were ripening their fruits.

This gives an idea of the density of garlic mustard in the study plots prior to cutting.

I am giving the test areas several weeks to show any recovery by cut plants, and will share the results in late June.

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Cruising for Crickets

by Carl Strang

Spring field crickets are singing in northeast Illinois, and it’s time to resume my study of field cricket geography in DuPage County. I’m trying to sort out why our two sibling species, the spring field cricket and the fall field cricket, don’t always occur together.

Green colors mark where I have found both spring field crickets and fall field crickets in previous years. Yellow locations had only fall field crickets, blue had only spring field crickets.

As you can see, there are large gaps I haven’t explored with respect to this question, so I plan to address this with some driving tours. The crickets sing loudly enough to be easily heard through open car windows when it’s calm, and sing consistently in the early evening, so that is when I have begun to seek them. The focus for now will be spring field crickets, and in the late summer I can follow up with a fall field cricket search.

Butterfly News

by Carl Strang

Butterflies continue to be diverse and abundant this spring, and last week brought some news to share from Mayslake Forest Preserve. Earlier I commented that question mark butterflies had a surprisingly delayed appearance, showing up in numbers on May 4 but not earlier as one would expect from overwintering individuals. I found a reference indicating that, like red admirals and some others we’ve been seeing this spring, question marks can migrate north in spring.

They looked fresh and clean in early May, like this one from a previous year, but last week I noticed that they now appear worn and tattered.

The butterfly highlight last week was an addition to the preserve species list.

This is the first gray hairstreak I have seen at Mayslake.

Also remarkable was an early-season eastern tailed-blue.

This relative of the hairstreaks usually doesn’t appear in noticeable numbers until mid-summer or so.

I made a mental note that I need to take a close look at all these little blue butterflies. Obviously I can no longer assume they are all spring azures.

Sorting Out Honeysuckles

by Carl Strang

Invasive bush honeysuckles are one of the main challenges in woodland restoration in northeast Illinois. Managing them doesn’t really require distinguishing the varieties, but in my preserve monitoring at Mayslake I feel I should have a handle on what is there. My old understanding was that there are two main forms, the Amur honeysuckle and the Tartarian honeysuckle. Over the winter I became aware that the botany is more complicated than that, and this spring I have done my best to sort it out. To keep things clear, in this post I will include scientific names in the main text rather than just in the tags at the top. Amur honeysuckle (Lonicera maackii) proves to be uncomplicated. The leaves are relatively big, and have drawn out or attenuated tips.

Amur honeysuckle, in fruit

The most common of the varieties I once referred to as “Tartarian honeysuckle” in fact is a hybrid, Lonicera X muendeniensis, the common fly honeysuckle.

Common fly honeysuckle, showing its white flowers. These turn yellow after a while, which would not happen in Tartarian honeysuckle.

Another hybrid, practically identical to the common fly honeysuckle except that the flowers are pink (but which likewise turn yellow in time), is the showy fly honeysuckle (Lonicera X bella). At Mayslake these are relatively few, and seem randomly scattered among the others.

This photo of one of the fly honeysuckles gives a good idea of the leaf shape, smaller and blunter than in Amur honeysuckle.

Having gotten this far, I ran into a few honeysuckles along Mayslake Forest Preserve’s 31st Street boundary that were distinctly different. These keyed to another species, Morrow’s honeysuckle (Lonicera morrowii).

The leaves are much larger and rounder than those of the fly honeysuckles, and the flowers are a little smaller.

All of this terminology is based on the most recent addition of the Swink & Wilhelm reference, Plants of the Chicago Region. Errors in identification are, of course, mine.

A Case of Displacement?

by Carl Strang

I recently returned from a brief trip out to Maryland for the wedding of my youngest nephew, Brice, to new niece Rachel.

My best photo from the ceremony, a symbolic blending of sands.

While staying at my brother’s house I took some morning walks, and heard unfamiliar crickets trilling. I had failed to bring recording equipment, and was unable to find one of the crickets. They were locally abundant ground-dwellers, but this was early in the season, which should rule out most possibilities even on the Eastern Shore. I believe these were southeastern field crickets, which have both spring and fall adults and are reportedly one of the most common crickets in their range. The song, a continuous trill interrupted by occasional stutters, was close to reference recordings for the species.

The thing is, I was hearing spring field crickets all along the drive out to Maryland, and that species is mapped throughout the DelMarVa peninsula, but I never heard one in the limited portion of that area I visited, mainly around Easton.

Spring field cricket

The Singing Insects of North America  range map for the southeastern field cricket establishes it in the southern tip of the DelMarVa peninsula, and Easton is just a short distance north of there.

Southeastern field cricket range map, from the Singing Insects of North America website.

So all of this has me wondering: was I in fact hearing southeastern field crickets, and if so, are they expanding north and, at least in the Eastern Shore area, displacing spring field crickets? Perhaps I will have more time and mobility on a future visit to check that out.

(Note: natural history information on southeastern field crickets from: Jang Y (2011) Male Responses to Conspecific Advertisement Signals in the Field Cricket Gryllus rubens (Orthoptera: Gryllidae). PLoS ONE 6(1): e16063. doi:10.1371/journal.pone.0016063).

Birds, Buckthorn and Oaks

by Carl Strang

Now that the early part of the migration season is past, I can do a preliminary test of the Birds-Buckthorn-Oaks hypothesis. The idea is that migrating birds seem to prefer buckthorn infested woodlands early in the migration season because the buckthorn understory provides shelter unavailable in restored, oak-dominated woodlands because usually the oaks have not yet leafed out to provide food and shelter. Data from last year supported this idea, because late-season migrants showed a shift from the buckthorns to the newly leafing oaks. This year a further, better test was made possible by the warm early season stimulating oaks to break buds early, so that they were well in leaf for the early part of the migration season. So, what did the data show? I compiled the numbers of neotropical migrants that don’t nest on Mayslake Forest Preserve that I counted prior to May 19 (when oaks began leafing last year), comparing last year’s counts to this year’s. The results were stark: I counted only 5 of those birds in the buckthorn woodland, compared to 22 in the restored savannas (compared to 80 and 34, respectively, last year. Numbers were low this year, in part because my back strain limited my outings, but also a lot of migrants seemed to be bypassing Mayslake).

Things are moving along. This olive-sided flycatcher, a late season migrant, stopped by Mayslake on May 14, earlier than usual.

Using last year’s proportions to calculate expected values if there had been no difference between years, the values would have been 18.9 in the buckthorn-dominated woodland, 8.1 in the savanna. It should come as no surprise that the resulting chi-squared test statistic showed a highly significant difference (34.07, even with only 1 degree of freedom, is far above the threshold). With the migration progressing so rapidly, I don’t know if there will be enough observations in the late season to consider separately, but if so there will be an additional post. Either way, I am satisfied that the data support my point.

Shaking a Photo Out of the Bag

by Carl Strang

I find myself caught up for the moment with ideas for blog posts, so today I’m just going to share the last outstanding photo I’d earmarked for the blog.

Male bufflehead, stream corridor marsh, Mayslake Forest Preserve.

This bufflehead appeared on the marsh earlier this spring. Last year a pair of them lingered for more than two weeks. This fellow just stayed 3 days or so and continued on his way. Not much of a story, just one of hundreds of observations in my preserve monitoring that generally don’t make the cut to be shared in this blog, but which collectively make up part of the daily story at Mayslake, and in that sense are important nevertheless.

Another Year’s Squirrel Data

by Carl Strang

At the end of March I completed my third year of collecting data on habitat preferences of fox and gray squirrels at Mayslake Forest Preserve. The basic question is whether the usual preference of fox squirrels for savanna habitat and gray squirrels for forest will hold in an area where the savanna is high quality and the forest is low quality.

Fox squirrel

Over the first two years it was clear that both species preferred the savanna, but that preference has been stronger in the fox squirrel. This year the results were a little different. The area involved, 54.6 acres altogether, is 64% savanna and 36% forest. In the first year, 82% of fox squirrel observations were in savanna, 90% in the second year and 92% in this year just ended. The corresponding numbers for gray squirrels were 73%, 79% and 65%. That last number was perhaps the most remarkable, gray squirrels in the past year appearing in the exact proportions of the two habitat types on the preserve.

Gray squirrel

That is the only number in this entire study that shows no statistically significant difference from expected values (actually, the chi-squared test statistic is calculated from the numbers of observations rather than the percentage values; this year I had 157 observations of fox squirrels, 75 of gray squirrels). I continue to gather these data each year because the preserve continues to change, thanks to the efforts of the restoration team. High quality savanna is improving, and low quality forest is being cut back.

Owlet Branched

by Carl Strang

The great horned owl nestling at Mayslake Forest Preserve branched on Wednesday of last week. That verb is applied to that species when they leave the nest because they are not fledging, still being flightless. Typically they climb out of the nest, climb down to the ground, walk some distance great or small to another tree, and climb up it. The Mayslake bird wasn’t quite so venturesome at first, simply going up two branches above the nest platform. That night, however, it traveled to another tree about 30 feet away from the nest tree.

It was in the very top of a tall oak.

A series of thunderstorms came through the night after I took that photo. The following day, Friday, the owlet was in the same tree but well below its previous perch. I had a night hike on Saturday, but by then the youngster had moved again and I did not find it. I hope to see it from time to time through the summer. There was only one youngster in the end. I say this with some certainty because when there are multiple nestlings they generally stick together when branching.

Here is an example from the Red Oak Nature Center a few years ago.

There is no way of knowing whether the surviving owlet is the one that spent some time at the Willowbrook Wildlife Center, or the one that stayed in the nest throughout. Even if the rescued bird eventually succumbed, the effort resulted in the installation of a solid nest platform that benefited the surviving nestling, and may well provide a base the parents will use again in coming years.

Testing the Birds and Buckthorn Hypothesis

by Carl Strang

A year ago I posted a hypothesis that this most unusual of seasons will allow me to test. To recap: When restored savannas are compared to woodlands with buckthorn and honeysuckle thickets in the understory in early May, when the bird migration is entering its peak, it seems that the birds prefer the invasive-degraded areas to the native savannas. Some birders take this as evidence that restoration is bad for birds. My hypothesis was that this observation is tied to the fact that oaks, the dominant trees in our savannas and woodlands, are among the latest trees to break bud and leaf out. Therefore they are not supporting leaf-eating insects, and also not providing the shelter that the birds need on their daytime migratory stops. As I pointed out a few weeks ago, like our flowering phenology, the oaks broke buds a few weeks early this year.

Remember this photo? I took it in early April, more than a month before oaks typically reach this point.

The stage thus is set. I have the records of where I saw the migrants last year, a late year when the oaks were not leafing out until the second half of May. I remarked in my notes that they were doing so around May 19, so I will take that as my dividing point. I can look at last year’s data, and this year’s, and see if the birds lose their apparent preference for the buckthorn woodlands now that they have leafy oaks as an alternative.

As a starting point I compared the bird counts from April 20 to May 18 last year to those from May 19 to May 31, when migration was essentially done. I considered only species that spend their winters south of the continental U.S. and that do not breed on the Mayslake preserve, to keep things as uniform and unbiased as possible. Even with those restrictions, I had 22 species to work with. For the moment ignoring species by species comparisons, here are the 2011 totals. In buckthorn woodlands before May 19, I made 80 observations of birds in the target group. The corresponding total for restored savanna areas in that same time period was 34 (these counts are not normalized for the relative areas of the two habitats, but the buckthorn area I used for this comparison is smaller, at 5.7 acres, than the savanna at 8.5). So the data support the notion that, at least early in the migration season before the oaks leafed out, the lower quality, buckthorn- and honeysuckle-dominated woodland harbored more birds. What about the latter part of the migration season, after May 18? Things had slowed down at that point, and the migrant species composition changed somewhat, but the totals last year were 24 observations in the buckthorn woodland and 28 in the savannas. Clearly the tide turned after the oaks began to leaf out (for the statistics cognoscenti, the chi-squared contingency table produced a test statistic value of 14.36 at 1 degree of freedom, highly significant). I will report on what happens this year, but if my hypothesis is correct, the oak savanna should prove more attractive to these migrants this year in both parts of the season.

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