May Phenology 3: Bird Arrival Dates

by Carl Strang

The pattern in the past has been for migrant bird arrival dates to be more similar between years than is true of flower and insect first appearances. Birds are capable of making small adjustments, but in general they are following the dictates of photoperiod, which observes the same calendar each year. Median arrival dates were thus only 3 days later at Mayslake Forest Preserve in 2013 than in 2012 (16 species), 8.5 days later than in 2011 (20 species), 1 day later than in 2010 (19 species), and 9 days later than in 2009 (19 species).

The eastern wood-pewee matched the median difference in arrival dates for both 2010 and 2009.

The eastern wood-pewee matched the median difference in arrival dates for both 2010 and 2009.

The respective differences for April and earlier were 7, 3, 2.5, and 5 days. The pattern of past years was sustained in magnitude, but it is also true that all median arrival dates were later in 2013 than in the other years. The late development of flowers and emergence of insects probably accounts for this. The birds can adjust their migratory timing that much.

Literature Review: Ornithology

by Carl Strang

Birds are the focus of this week’s literature feature.

The superb fairy-wrens of Australia have revealed yet another amazing wrinkle in their biology.

The superb fairy-wrens of Australia have revealed yet another amazing wrinkle in their biology.

Diane Colombelli-Négrel, Mark E. Hauber, Jeremy Robertson, Frank J. Sulloway, Herbert Hoi, Matteo Griggio, Sonia Kleindorfer. Embryonic Learning of Vocal Passwords in Superb Fairy-Wrens Reveals Intruder Cuckoo Nestlings. Current Biology, 2012; DOI: 10.1016/j.cub.2012.09.025

As described in a ScienceDaily article. They noticed that female superb fairy-wrens sing to their eggs, and they later demonstrated experimentally that the mothers were teaching their future nestlings a particular note, described by the authors as a password, that the nestlings would need to include in their begging calls to be fed. This note varies from nest to nest, and if the parents do not hear it they abandon. This is a novel way of dealing with nest parasites, in this case cuckoos, whose eggs and nestlings do not have the programming to learn and repeat the password.

Katzner, Todd, et al. 2012. Status, biology, and conservation priorities for North America’s eastern golden eagle (Aquila chrysaetos) population. Auk 129:168-176.

The eastern population estimate is 1000-2500 (east of the Mississippi River; western population 21,000-35,000). The species generally appears to be declining, though the eastern population has increased since the ban on DDT. Lead poisoning and incidental damage by leg-hold traps set for mammals are the biggest threats to eastern eagles. They are most abundant in Quebec, fewer in Ontario and Labrador as breeders. There has been no nesting in the eastern U.S. since the late 1990’s, the last ones in Maine and New York state. In Canada, nest sites are away from forested areas, mainly “at the interface of tundra, boreal forest, and wet meadows.” An estimated 15-25% migrate through the Great Lakes region. Wisconsin and Iowa host at least 70 birds in winter; the wintering status in Illinois is given as “unknown.”

The next study supports the idea that birds are more diverse in the tropical forests because of that biome’s greater age.

The next study supports the idea that birds are more diverse in the tropical forests because of that biome’s greater age.

W. Jetz, Thomas, G. H., Joy, J.B., Hartmann, K. & A.O. Mooers. The global diversity of birds in space and time. Nature, October 31, 2012.

As described in a ScienceDaily article. They did a combined fossil and DNA study of 10,000 bird species, and found unusual evolutionary diversification has been happening over the past 50 million years. Furthermore, the rate of new species appearance has not leveled off, but rather continued or even increased, in contrast to the usual pattern in which a foundational species diversifies but then a plateau is reached when available niches are filled. They attribute this difference to birds’ mobility, the opening of new habitats, and certain adaptable avian traits. Furthermore, there is no difference between speciation rates in the tropics and more polar regions, supporting a longer continuous history of tropical environments as being responsible for greater tropical diversity of birds (species accumulating, but extinction less rapid).

Stanley CQ, MacPherson M, Fraser KC, McKinnon EA, Stutchbury BJM (2012) Repeat Tracking of Individual Songbirds Reveals Consistent Migration Timing but Flexibility in Route. PLoS ONE 7(7): e40688. doi:10.1371/journal.pone.0040688

They followed individual wood thrushes over several migrations, and found that individuals showed little variation in spring migration departure date, and arrival date on territory, but much more flexibility in migration route and in fall departure date.

Brommer JE, Lehikoinen A, Valkama J (2012) The Breeding Ranges of Central European and Arctic Bird Species Move Poleward. PLoS ONE 7(9): e43648. doi:10.1371/journal.pone.0043648

They compared breeding bird atlases conducted in Finland, finding that there have been shifts northward in the centers of ranges for both northern and central European species. The shifts are happening slowly enough that surveys need to be taken decades apart. Northward advance of the northern edges of ranges is happening more quickly than extinctions at southern edges. The latter consideration is needed if range shifts are to be attributed to global climate change.

Phenological Comparisons at a Site

by Carl Strang

Today I am sharing the first of two presentations I made on Saturday at the biennial Wild Things conference in Chicago, a popular event where the region’s restoration and natural history enthusiasts share information. This was a brief 15-minute talk on my phenological observations at Mayslake, which I have shared piecemeal in this blog over the years. Here I simply repeat the points and graphics from the PowerPoint projection.

Some generalizations:

  • Phenological comparisons are best done on a reasonably small site, so other variables are better controlled (Mayslake 90 acres).
  • However, on a small site some species will be uncommon, reducing year-to-year consistency.
  • This is compensated in part by including as many species as possible.


Flowering phenology:

  • Flowering phenology is associated with soil temperature, so such factors as snow depth, severity of winter cold, and spring warmth are influential. 2012 had a warm spring following a mild, relatively snow-free winter, so flowering dates were unusually early.
  • As the season progresses, first flowering dates tend to converge between years.
First Flowering Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. The vertical axis gives the number of days median first flowering dates in each month were earlier in 2012 than in each of the other three years represented. For instance, in March 2012 flowers were appearing a median 32 days earlier than in 2009 and 2011, 21 days earlier than in 2010.

First Flowering Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. The vertical axis gives the number of days median first flowering dates in each month were earlier in 2012 than in each of the other three years represented. For instance, in March 2012 flowers were appearing a median 32 days earlier than in 2009 and 2011, 21 days earlier than in 2010.

Bee fly b

Insect phenology:

  • Insects mainly overwinter in the soil or under water, and so their first appearance phenology to some extent tracks that of first flowering dates.
  • Insects often have small first generations which can be missed, leading to large differences between years. Sample size helps, as well as intelligent data interpretation (knowing individual species’ natural history).
Insect Species First Appearance Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. This graph is set up just like the previous one. Note that the position of the “0” line, representing no difference in median dates in a month, is different from the first graph.

Insect Species First Appearance Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. This graph is set up just like the previous one. Note that the position of the “0” line, representing no difference in median dates in a month, is different from the first graph.

Baltimore oriole 4a

Migrant bird spring arrival phenology:

  • Bird phenology does not vary so much between years, especially for Neotropical migrants. Therefore, differences are greatest before the end of April.
Migrant Bird First Arrival Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. Graph set up like the first two.

Migrant Bird First Arrival Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. Graph set up like the first two.

Flower and insect phenology, influenced as they are by local winter and spring weather, follow parallel patterns with warmer years producing earlier flowering dates and insect appearances. Birds, coming from outside the area, are less subject to these influences though the birds that arrive earlier in the spring, coming from the southern U.S., may be experiencing similar weather and so respond accordingly. Neotropical migrants are unable to respond to such influences and so appear at close to the same dates each year, beginning in late April and early May.

May Bird Arrival Phenology

by Carl Strang

May is the last month in which I track migrant bird arrival dates at Mayslake Forest Preserve, as the spring migration is practically concluded. As has been the case this spring, median bird arrival dates have not been nearly as different from previous years as those for first flowers or insect appearances. The 22 species I could compare between 2012 and 2011 were a median 4.5 days later this year, ranging 9 days earlier to 38 days later. The median difference from 2010 was exactly 0, or no difference, with a range of 8 days earlier to 19 days later for 20 species. Finally, 21 species arrived a median 5 days later than in 2009, ranging 10 days earlier to 26 days later.

The rose-breasted grosbeak was fairly typical, the first arriving at Mayslake on May 4 this year, May 2 last year, May 4 in 2010 and April 27 in 2009.

As I mentioned when summarizing data on bird preferences for buckthorn vs. oak woodlands, this year was characterized by a number of migrant species bypassing Mayslake altogether, so there were many for which comparisons could not be made.

Birds, Buckthorn and Oaks Final

by Carl Strang

As I mentioned in my previous post on this subject, the songbird migration was nearly done by mid-May. In fact I have only 3 observations to add to the ones from the early part of the season, two in the oaks and one in the buckthorn-dominated woodland. That mildly reinforces my earlier conclusion, that the only reason buckthorn woodlands appeal to birds early in the season in our area is that oaks, which dominate most of our woodlands, leaf out late. In this year when the oaks were in leaf throughout the migration season, songbird migrants nearly abandoned the insect-depauperate buckthorn at Mayslake Forest Preserve and spent their time in the oak woodlands.

South savanna at Mayslake, showing oaks well leafed.

So far all the analysis has been of the total species counts of neotropical migrants that do not nest at Mayslake. However, some of those species are brush specialists that might be expected to prefer the buckthorn over the more open oak woodlands regardless of what is happening in the canopy.

The Tennessee warbler is an example of a canopy species, on the other hand, which will not want to spend a lot of time foraging down in the buckthorn, though they might want to have it handy for resting and as a refuge from predators.

When I look at the two years’ data, sorting out brush from non-brush birds, the most curious observation is that hardly any brush-loving birds stopped by Mayslake this year. Only two birds out of the total sample of 30 were of brush species. Last year, 38 of 166 were brush birds. Looking at 2011, then, both brush and non-brush birds preferred the buckthorn woodland early in the season, though the preference was stronger for the brush species. Late last year, after the oaks were leafing out, non-brush species preferred oaks while the brush birds did not show a strong preference for either woodland type.

All of these data, coming as they do from one site over a short period of time, amount to a pilot study at best. Nevertheless, they support the notion that the apparent preference of migrant songbirds for woodlands dominated by invasive shrubs is an illusion. Birds avoid the buckthorn and prefer restored native woodlands when the latter are in leaf, capable of providing both food and essential shelter.

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.

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.

Migrant Bird April Arrivals

by Carl Strang

In contrast to the much earlier flowering dates and insect appearances that I recounted in the previous two posts, April’s birds arrived on dates much closer to those of earlier years. Median dates were 4 days earlier in 2012 than in 2009, 0.5 day earlier than in 2010, and 2 days earlier than in 2011.

One of the April birds that had traveled the farthest was the chimney swift. Following their instinctive schedule, the first of these appeared at Mayslake Forest Preserve on April 19, not much different from 2009’s date of April 24, April 21 in 2010 and April 25 last year.

The medians represent samples of 13, 14 and 13 species in the three comparisons, respectively. The largest range was the comparison to 2009, at 21 days earlier to 26 days later.

Lesser scaup first stopped by May’s Lake on April 5, distinctly later than the dates of 10 March, 16 March and 31 March in 2009-2011, respectively.

The contrast with flower and insect phenology is stark, and indicates how responsive those two groups are to local conditions. These birds wintered well to the south, have no idea of local conditions, and simply follow the dictates of their biological clocks and instincts. I expect to see little difference in May as well.

Migrant Bird Arrivals

by Carl Strang

Today I conclude my review of early season phenology by considering arrival dates of migrant birds at Mayslake Forest Preserve. A few of these data are from late February, most are from March.

The eastern phoebe usually begins to arrive in March. This year, the first phoebe appeared at Mayslake 6 days earlier than in 2011, 11 days earlier than in 2010, and 9 days earlier than in 2009.

Bird arrival dates did not show quite the dramatic differences from previous years as did first flower dates or first insect appearances. Nevertheless, birds were showing up early in February and March. Relative to 2011, 16 bird species appeared a median 4.5 days early in 2012 (range 23 days earlier to 21 days later). The difference was larger in comparison to 2010: 15 bird species arrived a median 11 days earlier (range 0-31 days earlier). Finally, 16 bird species appeared a median 3 days earlier in 2012 than in 2009 (range 9 days earlier to 13 days later).

So far, the birds we are seeing are species that spent the winter in the southern U.S. They are expected to be much more responsive to weather conditions than the tropical migrants, which could not know about the early season. Therefore I expect differences in arrival dates to diminish as the migration season progresses.

Lessons from Travels: Migrants Elsewhere

by Carl Strang

When we are at home in Illinois, we categorize our birds with respect to their status when we see them here. They may be year-round residents, breeders that migrate south for the winter, winter residents, or migrants that breed north of us and pass through in the spring and fall. Those categories do not define the birds from their own perspective, however, and we can get some sense of this when we see them perfectly at home in other places. When we think of yellow-throated warblers, for instance, we typically associate them with sycamores, not with palm trees.

Yellow-throated warbler in Belize.

Still, there is a consistency in the open canopies of sycamores and palms that makes sense from the bird’s perspective. Though we commonly think of our breeding birds as being northern animals that head south to escape the winter, it might be better to regard them instead as tropical birds that travel north to take advantage of high summer productivity and fewer predators.

Travel also allows us to broaden our perspective on migrants, when we see them on their breeding grounds. This was one of the side benefits of the summers I spent in western Alaska. On the rare occasions when we see long-tailed ducks in northeast Illinois they are quiet, placid, unobtrusive. They are quite the opposite on their breeding grounds.

Male long-tailed duck, Kokechik Bay study area.

When courtship commences they become very noisy with un-duck-like tenor voices, chasing each other at rocket speeds and coming very close, apparently using people as picks. The females incubate large clutches of eggs, producing tiny dark ducklings.

In those days we called them oldsquaws. Here a mother and ducklings share a pond with red-necked phalaropes, which then were known as northern phalaropes.

Tundra swans have extraordinary courtship and territorial displays, and make huge nest mounds. Biologists can count eggs from the air. The young are placid.

Nonbreeders gather into flocks of 30 or more.

In the treeless tundra, dunlins advertise by hovering 10 feet above the ground, trilling a song that is almost identical to that of American toads. They have well camouflaged ground nests with 4 eggs.

When we see them as migrants in Illinois, dunlins are traveling in small flocks and behaving as shorebirds.

Jaegers are rarely encountered seabirds in Illinois, sought along the edge of Lake Michigan especially during the fall migration. On the breeding grounds they are predators.

Long-tailed jaegers are beautiful and graceful, hovering like kestrels in their hunt for tundra voles and bird eggs.

Two species nested there, the other being the parasitic jaeger.

Parasitic jaegers are larger than long-taileds. Once I saw one chase down and swallow whole an adult red-necked phalarope.

Such experiences sit in my mind, reminding me to think of these animals in terms of their entire lives rather than the more limited glimpses we see in Illinois.

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