Species Dossier: Common Nighthawk

by Carl Strang

This week’s species dossier features a bird which in DuPage County is a migrant rather than a breeder. That is unfortunate, because the spectacle of a hunting nighthawk in summer was a special delight in my younger days.

Nighthawk, Common

Generally these are seen in the air. They also roost (nest?) on buildings, large horizontal tree branches near woods edges, temporarily on deserted streets in early morning, and on rocks in the prairie. They were summer residents in Culver and Lafayette, Indiana, there were a few in Carlisle, Pennsylvania, but they are essentially absent as breeders in DuPage County although they are abundant migrants there, with rivers of them passing over in spring and fall. They feed on aerial insects, sometimes chasing them spectacularly high above the ground. They show some evidence of territoriality when breeding, with aerobatic chases, steep dives with sudden upward turns and twists. Many were brought to the wildlife hospital at Willowbrook in the early 1980’s, wings broken by wires. Adults almost always died; they had to be force-fed and didn’t take the stress well. Some young birds would beg, however, and a few made it. In the clinic they showed an impressive threat display, opening the enormous pink-lined mouth and hissing.

14AU86. First fall migrants in DuPage County, IL.

15MY87. First of year (several) passing over Geneva.

16MY87. One resting on fence rail in front of house at Summerlakes subdivision, Warrenville. I approached within 7 feet and took several photos before it suddenly popped into flight.

Nighthawk roosting on decorative fence rail in a Warrenville subdivision.

10SE87. Bulk of fall migration over. An occasional individual in the evening, yet. 3 seen on 16SE the last noted for 1987.

10SE88. Still a few migrants.

27MY99. Nighthawks migrating over Willowbrook, evening.

JE99. Horsethief Trail, central Kansas. Nighthawk flying and calling at 1pm.

18AU99. First migrating nighthawks, DuPage County.

27AU00. Nighthawks have been common, passing through Warrenville the past week. Today at Illinois Beach State Park in the Natural Area I photographed one sleeping on a horizontal branch of an Austrian pine.

Autumn migrant roosting on a tree branch, Illinois Beach State Park.

23MY02. The first evening I’ve noticed many passing over. At Elsen’s Hill, some were flying low over the river to feed.

25MY02. At Meacham Grove after 10a.m., one flying over marsh area.

29SE11. Mayslake. An unusual group of 5 nighthawks passing over the preserve at mid-day, late for them.

May Phenology: Migrant Birds

by Carl Strang

May is the main month in northeast Illinois for arrivals of migrating birds that spent their winter in the tropics. I compare first observation dates of each species between years as part of my phenology study at Mayslake Forest Preserve. As I noted a month ago, birds are less influenced by weather than are insects and plants, which form the other two legs of my phenological comparisons among years. This was the case in May as well.

The first chestnut-sided warbler to appear at Mayslake this year was representative of the whole, arriving 4 days later than in 2010, 2 days later than in 2009.

Median arrivals in 2011 were not much different from those of the previous two years. The median vs. 2010 was 3 days later, and 2 days later than that for 2009. Differences were more dramatic for plants and insects, as I’ll show tomorrow.

Oak Leaves Expand

by Carl Strang

Last week I described the preference migrating songbirds were showing for an inferior woodland, rather than the high quality savannas at Mayslake Forest Preserve. I thought the security provided by the woodland’s buckthorn understory might be the significant factor. This week I found some support for that idea. The oaks have expanded their leaves.

Bur oak is the dominant tree in Mayslake’s savannas, followed by white oak, shagbark hickory, and Hill’s oak.

The migration is winding down, but there has been a clear shift of warblers, vireos and others into the savannas. The few remaining in the degraded woodland are species like yellow-bellied and alder flycatchers, which like low dense brush. Now that there are lots of hiding places in the oak canopy, it seems, that is the place to be.

Birds and Buckthorn

by Carl Strang

Birds eat bugs. That’s a 3-word description of the main action going on these days as migrant songbirds drop into our woodlands, refueling during the day before they continue on their way north at night.

Buckthorn provides no bugs, nor does honeysuckle. These Eurasian shrubs might as well be made of plastic, as far as our native insects are concerned, and so support none of the fuel needed by those feathered foragers.

So, why does it so often seem that more migrants can be found in woodlands with buckthorn and honeysuckle understories rather than restored woodlands with a diversity of herbaceous native plants beneath the trees?

This has been the hottest part of Mayslake Forest Preserve in recent days for diverse migrant songbirds. Its dominant understory plant is buckthorn. The nearby restored savanna, rich in native herbs, has some migrants, but not nearly so many species or individuals.

Some people who are excellent birders (but uninterested in ecology or any other aspect of natural history) have made similar observations, and so have a negative view of restoration.  It’s hard to blame them, given their data and focus.

So, what’s going on here? I have a hypothesis, but it needs testing (unless someone already has done so and I haven’t encountered the paper). I think the issue is security.

Here a Wilson’s warbler rests in the dense foliage of a buckthorn bush in the same area at Mayslake.

Both the savanna and the buckthorn-infested woodland have plenty of trees, and most of the insects these birds are after are feeding on the trees’ flowers and tender new leaves. The herbaceous plants in the savanna will provide abundant insects later in the season, but not much to speak of, this early. In other words, food availability probably is similar between the two kinds of places during this peak migration time (a test of my hypothesis would require measurements to confirm that statement, however).

I suspect that the buckthorn’s appeal is that it provides a ready hiding place for the migrants. They want a secure retreat if a hawk comes along, and the blanket of dense shrubbery beneath them has that quality. As dawn breaks, birds that have been flying all night are looking for a place to spend the day. Trees provide the food, and the dense patches of understory shrubs complete a clear target for weary, hungry, safety conscious birds.

April Phenology

by Carl Strang

April is the first month when I can begin to make phenological comparisons between years. I look at three sets of data from Mayslake Forest Preserve: first flowering dates, arrival dates for migrant birds, and first appearances of insects. I continue to find new species, which of course can’t be used in this analysis. One example this year was the purple dead nettle.

Not really a nettle, the plant’s square stem and lipped flowers demonstrate its place in the mint family.

This is the third year of this study, and 2011’s April flower phenology fell between 2009 and 2010. There were 8 species that bloomed earlier than in 2009, and 5 later, placing this April fairly close to 2009’s very late season. That should surprise no one. Compared to 2010, there were 3 species that flowered earlier and 12 later.

Animals showed less distinction among years. For insects, 2011 brought the earliest arrival among the three years for 3 species, 2 species were latest, and 2 species appeared between their 2009 and 2010 dates. Likewise, bird arrivals in 2011 were earliest for 10 species, latest for 4, and in the middle for 8. Birds, governed more by photoperiod, are somewhat influenced by weather but not nearly as much as flower dates, which are tied to soil temperature.

Sparrow Phase Already!

by Carl Strang

The last of the warblers still are shaking themselves out of the North, but there is no question that the migration season is shifting into its later stages. This week, sparrows appeared at Mayslake Forest Preserve in an unambiguous signal of the season. The prairie garden north of the chapel attracted a mix dominated by white-crowneds.

There also were some Lincoln’s sparrows, the first I’ve seen at Mayslake.

Unphotographed but also present were a swamp sparrow, a number of white-throateds, and (death knell for the warm season) the first juncos. Also unphotographed were my first Mayslake rusty blackbirds, still half in black feathers, half in their new winter browns as they foraged in the stream corridor marsh. Other migrants have been a presence for some days, now.

Yellow-rumped warblers have been abundant, showing their wide ecological range as they forage for insects on the ground, in the trees, in mid-air sallying flights, and also gulp down cedar berries.

Cedar waxwings likewise have been feeding on both insects and fruits. Here a few engage in plumage maintenance.

Enjoy this diversity while you can. Winter is coming!

May Phenology

by Carl Strang

It’s time to update my record of flowering phenology at Mayslake Forest Preserve. Through April, plants were blooming a median of 13 days earlier than in 2009. In May I have an additional 41 species to report. Five of these were new to the list, and so I have no 2009 dates for comparison. These include nannyberry, about which I reported earlier. Other new shrubs are black raspberry, and autumn olive (shown).

I am not sure how I missed a prominent trailside patch of common speedwell last year.

Even more intriguing is this one:

Clearly a member of genus Senecio, this single plant keyed to butterweed. It is blooming close to the center of the preserve, so I am not sure how it got there. Butterweed is not native, and apparently is not commonly encountered in northeast Illinois, though DuPage Forest Preserve District botanist Scott Kobal tells me he has found it much more frequently in recent years.

Returning to the species for which I had flowering dates in 2009, I had to divide them into two groups. I was out of town for significant portions of May, and so found 16 species blooming profusely that had begun in my absences. The dates I was able to record for them certainly were later than their actual first flower dates must have been. The median was 3 days earlier than in 2009, range 15 days earlier to 5 days later.

Of more interest were the 20 species for which my 2010 first flower dates were reasonably close to the actual. There the range was 4-23 days earlier, with a median of 13. At least so far, 2010 flower phenology continues to be significantly ahead of 2009.

Curiously, migrant bird arrivals do not show the same pattern. The 15 species whose May arrival dates I can compare reasonably between years all appeared later in 2010 than in 2009. The range was 3-15 days later, with a median of 8 days. No explanation immediately comes to mind.

Bird Arrival Dates Through April

by Carl Strang

Two days ago I reviewed flowering phenology at Mayslake Forest Preserve, which demonstrated that spring is progressing about two weeks ahead of last year. Today I want to consider whether migrant birds are showing a similar pattern. There are two questions that interest me. First, is there a difference between species that winter in the tropics versus those with at least a significant presence in the southern U.S.? If weather is a factor, we might expect the closer birds to be more responsive. Second, did the U.S.-wintering species arrive earlier in March and April this year than last? Here’s one of those species, an eastern phoebe, already incubating a nest at Mayslake.

As of the end of April, not many tropical migrants had arrived. All four of those that I observed were within 6 days of their last year’s arrival date (two were earlier, two later; median 1.5 days earlier). Since they are responsive to physiological clock and day-length signals that are the same between years, this is the kind of tight pattern I would have expected.

The 27 species that wintered in the southern U.S. showed a lot more scatter, with arrival dates ranging from 40 days earlier to 21 days later. The median difference was only 2 days later, however, which leaves me thinking that these birds, as a group, likewise did not respond to the early spring. This, like the flowering phenology, I will want to follow in future years, with the elaboration of looking at the data on a species by species basis.

Early Bird Arrivals

by Carl Strang

The migration season still is young, but already we are seeing the northward push from birds that wintered in the southern U.S. Tropical migrants will be arriving soon. At Mayslake Forest Preserve I have added a few new species to the all-time preserve list. These include horned grebe, a couple of which spent a few days on May’s Lake.

I never had encountered any yellow-bellied sapsuckers at Mayslake before last week, when two different individuals stopped by. Here’s one of them:

An osprey lingered and fished May’s Lake for more than a week, recently.

One of these piscivorous raptors stayed several days last year, as well, though later in the season. And, of course, the usual customers have been appearing in good numbers.

Robins will nest.

Cowbirds will not, though they will deposit plenty of parasitic eggs in host nests. Many of these migrants are showing up earlier than they did last year, reflecting the relative warmth of this spring. Tropical migrants are less influenced by weather, and probably won’t appear in numbers before the last week of April.

Literature Review: Monarch Navigation

by Carl Strang

If I had to choose one scientific journal to follow, it would be Science. Not only is this the most prestigious American journal (on par with Europe’s Nature), it is available at many public libraries and all college libraries. In addition to the original scientific papers published in Science, there is excellent reporting on results published elsewhere. Today I want to focus on one of the papers published in Science last year:

Merlin, Christine, Robert J. Gegear, and Steven M. Reppert. 2009. Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies. Science 325: 1700-1704.

One of the wonders of nature in North America is the monarch migration. Each autumn, monarch butterflies from across eastern North America fly to a small area in the Mexican mountains and spend the winter there. They are removed by several generations from their ancestors who last made the trip. How do they navigate?

These three researchers looked at an aspect of this question. They knew from earlier studies that monarchs orient toward the sun to move in a southerly direction during their fall migration. Furthermore, the butterflies use a physiological clock (consisting of certain chemical reactions) to tell them where the sun is relative to south. This study found that the clock is located in the antennae rather than in the brain as had been thought. I would have guessed that persistent pheromones were involved somehow in monarch navigation, the butterflies perhaps following gradients of concentration with the aid of sensitive chemoreceptors in the antennae. It seems from this study that the antennae are indeed involved, but in a completely different way.

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