Tennessee Warbler Dossier

by Carl Strang

The Tennessee warbler is one of our more abundant migrants, conspicuous more by sound than by sight in spring as it is well camouflaged and moves slowly, often high in the trees. It often works closer to the ground and more frenetically in the fall.

Warbler, Tennessee

Tennessee Warbler

Tennessee Warbler

Seen as migrant in many locations in the eastern U.S. Judging by songs, one of the most abundant warbler migrants. Not an easy bird to see; moves slowly and infrequently, and colors cryptic among tree leaves. Song loud and distinctive, and for a week or so every spring the trees of woods and residential areas ring with their songs. “Sebit, sebit, sebit, sebit, seteeteeteeteetee…” Initial part just like Nashville warbler’s, but last part very loud, rapid and energetic with no slurring of notes.

10MY87. First of season noted.

13MY87. At Willowbrook, one bird thoroughly working one small area, with much turning of its head, short reaches to probe nearby leaves, short hops between branches, relatively slow-moving for a warbler. Also does a lot of slow smooth stepping along a twig. Foraging in box elder, black willow.

13SE87. West DuPage Woods Forest Preserve. Several Tennessee warblers together in a mixed flock with a magnolia warbler, a red-eyed vireo, a female rose-breasted grosbeak, and several catbirds and robins. The warblers remained within 10 feet of the ground, active and acrobatic, probing, changing perches frequently (2-10 seconds), very chickadee-like and unlike last spring. 11MY88. First Tennessee warbler song of the year. Gone by May 20.

18MY90. Lots of Tennessee warblers at Willowbrook. Cold spring. The only warblers heard on the 24th.

4MY99. First migrant noted at Willowbrook. Last noted there on 25MY.

12MY99. Slow and deliberate, on 1 perch a long time as they look around.

31AU99. First migrant noted at Willowbrook. First-year Tennessee warbler very yellow, with yellow eye line, but white under tail. In contrast to spring birds, very frequent perch changes, actively pivoting and reaching. Last migrant at Willowbrook noted 17SE.

7MY00. Several Tennessees in a mixed flock at West DuPage Woods, high in canopy. One was moving steadily when I first saw it, foraging and singing, then was still for over a minute on a perch, apparently doing no foraging, but alternating singing with bouts of preening.

24SE00. Tennessees have been abundant, lately. Today, a couple in hedgelike borders of the Prairie Path at West Chicago Prairie just east of Industrial Drive.

8OC00. A couple Tennessee’s at West Chicago Prairie.

12OC02. A few at Fermilab in old field areas.

Mayslake Birds Update

by Carl Strang

The birds have completed their nesting for the year, and some already have departed for the South.

It has been a while since Mayslake Forest Preserve’s eastern kingbirds have filled the air with their distinctive chattering.

Mayslake is not a migrant mecca, but we get a few. The mixed flocks usually build themselves around the local black-capped chickadees, whose frequent calling and local knowledge make flock cohesion possible and worth maintaining. One recent flock contained 2 chickadees, a redstart, 2 magnolia warblers, a black-and-white warbler, a black-throated green warbler, and a chestnut-sided warbler.

The black-and-white warbler crawled the tree bark, while the other species hunted insect prey in their various other specialized ways.

Another flock on the same day included a chickadee, a redstart, a house finch, a downy woodpecker, a white-breasted nuthatch, and a house wren. Resident birds like the woodpecker and nuthatch often join these flocks. A final grouping that day included 3 chickadees, a Nashville warbler, and a warbling vireo.

The Nashville warbler

September birders know to key on the chickadee calls. The migrants certainly do.

P.S., this is the 900th post of this blog.

Golden-crowned Kinglet Dossier

by Carl Strang

Here is my dossier for another northern species which often winters in northeastern Illinois in small numbers.

Kinglet, Golden-crowned

Migrant in northern Illinois, northern Indiana. Flight has the quality of falling snowflakes. Two foraging together at Willowbrook in early 1986 gave a contact call whenever flying between trees in which they were foraging. Song jumbling, chattering in high-pitched, thin tinkling voice.

1AP87. First of year seen.

3AP87. Willowbrook. The kinglets are as acrobatic as chickadees, but less assertive and so less noticed. A male fed at edge of the stream, hopping on mud, rocks, sticks, picking at ground, snapping at air, picking tiny things from water. Crest center yellow, but parts or all became red for split-second periods, either from change in bird’s orientation to light, or from minute elevations and depressions of feathers.

10AP87. A kinglet approached within 3 feet of me, hopping on sticks low to the ground.

11AP87. Maple Grove Forest Preserve, IL: Kinglets in trees, 10-40 feet up.

15AP87. Golden-crowneds done passing through.

4NO87. A Missouri state park south of St. Louis. Golden-crowned kinglets behaving much as I have seen them in spring migrations.

16AP88. Morton Arboretum. Flock feeding in forest treetops.

29AP88. Golden-crowned kinglets still present.

15OC88. First fall migrants, Warrenville Grove Forest Preserve.

18OC88. Foraging with yellow-rumped warblers.

31MR89. First of year seen, Willowbrook Back 40.

22AP89. Both kinglet species at Willowbrook. Both using a mix of hover-gleaning and even more pursuit.

24AP89. Still there. May only use movement-contact call when scattered out. Those on 22nd, foraging in easy view of one another, weren’t using it while today they are.

17AP90. Observed at Willowbrook.

31MR99. Many kinglets foraging along stream, Willowbrook.

12AP99. Willowbrook. Golden-crowned kinglets nearly gone (saw only 1), but ruby-crowneds have arrived. Last G-crowned in spring seen on 14AP.

5OC99. First migrant of fall noted at Willowbrook. Last seen 21OC.

11MR00. First kinglet of year at Willowbrook, only 1 seen. 3-syllable high-pitched contact call distinctive [for some reason it took me this long to learn to recognize this common call].

One reason I mentioned foraging technique so often is that, according to the literature, golden-crowned kinglets reach for food from perches more, while ruby-crowneds hover-glean and use flush-and-pursuit more. These behavioral differences are consistent with slight proportional differences in wing and foot length.

26MR00. West DuPage Woods. Today they are foraging high (20+ feet up), in canopies of white oak and other forest trees. One moving steadily, with hops of 1-3 inches mainly, occasionally larger jumps between major branches and trees, both reaching and hover gleaning. Hover-gleaning pursuits of 1-2 feet. In mixed flock with creepers and 2 white-breasted nuthatches. Another kinglet moved 6″-2′ between perches, remaining 2-3 seconds per perch with head constantly turning.

27MR00. Willowbrook. A number of golden‑crowned kinglets and 3 brown creepers observed. Kinglet contact notes usually more emphatic, in groups of 3 or 4. Creeper notes similar in pitch and tone, but a little fainter, more drawn out, and single notes evenly spaced as the bird flies between trees (spacing a little greater than the notes of the kinglets).

31MR00. Waterfall Glen, beside Sawmill Creek, several golden-crowned kinglets in apparent mixed flock with brown creepers and a couple white-breasted nuthatches. One moving 4″-2′ between perches, most often around 1 foot, with occasional flycatching move but most often flying to a perch and immediately reaching for something. The reach was done with no searching after landing, and so the bird had spotted the prey and flown to it. Later, I encountered another group of kinglets with chickadees nearby. One made shorter, 1-2″ hops with much looking around, 8-10 feet up in tree. I saw no foraging moves.

1AP00. Heritage Trail, Morton Arboretum. Several in mixed flock with chickadees and a white-breasted nuthatch. High, 40-50 feet in crowns of white oaks. Kinglets moving more constantly than chickadees, with smaller hops, doing a lot of reaching for prey.

13AP00. Willowbrook. Golden-crowned kinglets and ruby-crowneds both have been at Willowbrook all week.

22AP00. Morton Arboretum. Both kinglets still present.

2AP01. First golden-crown of the year at Willowbrook.

29-31AU01. Algonquin Park, Ontario. Small groups of golden-crowned kinglets frequently encountered, one of the more commonly observed birds, easily located by their contact calls. Almost always in association with black-capped chickadees. Once or twice, perhaps, not with other birds I could see. Usually seemed to be 3-5 individuals in a group, and almost always if not always in conifers. Note: the branches are fairly dense in these forests, promoting a reaching foraging style. Are forests more open farther north, where ruby-crowneds live, so that a hover-gleaning style is favored?

1FE02. One or two feeding with chickadees at Waterfall Glen, just east of Poverty Savanna area.

18AU04. Sleeping Giant Provincial Park, Ontario. A golden-crowned kinglet showed very unusual behavior as it foraged among balsam fir branches hanging out on the trail. It did a lot of hovering just beyond the branch tips, visually scanning as it did so. Perhaps it’s a young bird that will learn to abandon this energy-wasting behavior.

9OC05. West DuPage Woods. Golden-crowned kinglets foraging in crowns of trees while ruby-crowneds are mainly within 4 feet of ground in herbs and shrubs beneath, only occasionally and briefly venturing into the lower canopies. Ruby-crowneds have a quick, chattering-quality “checkit” call. Hover-gleaning their most common foraging method today.

5-11NO05. During my southern vacation, I found golden-crowned and ruby-crowned kinglets all the way to the Gulf of Mexico.

16AP09. Golden-crowned kinglet, late in migration and apparently alone, uttering a different call. Same pitch as usual, but a longer burred call much like the rougher waxwing call.

Black-capped Chickadee Dossier

by Carl Strang

I have mentioned black-capped chickadees from time to time in this blog, most notably when introducing the topic of mixed flocks. Today I want to share my dossier on this species. In my dossiers I try to summarize what I know of a species from my own observations, as opposed to information from the literature or other outside sources. I began writing the dossier in the mid-1980’s. Observations begin with my date codes.

Chickadee, Black-capped

Ca. 1979. I remember sitting on the hawk watch at Reineman Sanctuary in PA in fall and watching as a sharp-shinned hawk zipping along the ridge suddenly turned its course so as to enter the tree canopy and caught a chickadee.

Boiling Springs, PA, 1980. A pair nested in hollow Ailanthus branch. One bird was electrocuted by a nearby electric fence. The other completed incubation and at least began to rear the brood alone. “Cheeseburger” call (more formally known as the fee-bee call) used early as apparent territorial signal.

Lombard, IL, 1981. A pair nested in a wren house, raised a brood, then returned and raised a second brood in the same house. In both cases, the pair traveled the neighborhood with their groups of fledglings.

Maple Grove Forest Preserve (F.P.), 1986. A pair was cleaning out an old cavity in a 10 foot snag in the maple forest. The excavating bird periodically removed beaks full of sawdust. Other bird remained nearby, giving occasional “chickadee” contact call.

Meacham Grove F.P., 24MY86. For the first time, I saw a chickadee taking advantage of tortricids hidden in folded leaves. One individual moved from one folded leaf to the next, vigorously tearing them open. I expected to see it more frequently than I have, given the lack of other birds with the appropriate foraging behavior in their repertoire, and the abundance of this food resource.

Willowbrook F.P., 1984-86. Chickadees have broods in the wooded riparian strip each spring. One pair appears to control the entire 1/4 mi. X 100-foot strip. Groups of more than 2 chickadees stay together through the winter. “Chickittaperk” vocalization appears to be an interspecific agonistic (dispute) display.

Chickadees weren’t common in Culver, Indiana when I was growing up. I remember being pleasantly surprised that a pair was present, nesting, at Miracles’ house in summer. This implies they were more easily seen in winter, at the feeder. Old trees and branches were scarce in our neighborhood.

Alarm call: one used a sharp “chiburr,” another answered with the same call.

11FE87. Willowbrook. Widely scattered chickadees in the Back 40 old field are maintaining contact mainly via the feebee call.

28FE87. A group of a half-dozen chickadees in trees: much sneeze-calling and chick-chick-chick-chick, but few chickadee calls, with much chasing and displacement. Later, many individuals made chickadee calls from widely separated perches. Then a period of silence followed.

14MR87. Maple Grove F.P. Seven chickadees moved together with a mix of chickadee and sneeze calls, occasionally briefly chasing one another. The group spread out widely, then used very high-pitched brief “cheeks” for contact.

29AP87. Chickadee caught adult noctuid moth, pecked body (scales puffed into the air), removed wings one at a time and they drifted to the ground, landing at least 3 feet apart.

1JL87. Willowbrook F.P. Chickadee pecking at mulberries.

10SE87. 0.5-3 seconds per perch in foraging, flying or hopping a few inches to 6 feet or occasionally 10 feet between perches, acrobatic hanging or hover-gleaning, pecking at dried leaves, turning and lowering body almost to upside down position to peer different ways.

13SE87. At West DuPage Woods F.P., several chickadees in a mixed flock with a redstart and a bay-breasted warbler.

17JE89. A broad-winged hawk callied repeatedly, in north end of Maple Grove F.P. Jays, flickers and grackles were highly agitated, flickers the most continuously vocal with “keels” every 2 seconds (2 birds). Grackles gacking frequently, too. A great crested flycatcher near, also vocal, but not clearly in response to the hawk; same with chickadees. Robins definitely disturbed, with nervous dee-dee-dee’s every 20 seconds or so. Jays in bursts, with several birds mobbing.

10JE90. Warrenville Grove. Chickadee saw me at sit near edge of woods. Alarm call “chicka-chicka-…(rapid)-dee-dee-dee”

3JL90. Chickadee plucked 2 unripe (white) mulberries from the branches. Dropped the first, then went for the second. Worked on it several seconds, holding it against a twig with its toes. I couldn’t tell if it ate the whole berry or just extracted seeds. Suspect latter.

7SE90. 2 chickadees eating dried crabapples, eating, pulling out and eating little bites.

30SE90. Chickadee and downy woodpecker eating poison ivy berries at Ann’s business property near Lafayette.

8FE00. Chickadees heard singing for the first time of the year at Willowbrook, and continuing in the following days. Also vigorously chasing each other this day, with agonistic vocalizations.

10FE00. Chickadees singing (feebee song) at Willowbrook.

1AP00. Morton Arboretum, Heritage Trail. A mixed flock with at least 1 brown creeper, 2-3 chickadees; juncos and robin in area. Chickadees longer on each perch than golden-crowned kinglets observed yesterday. A lot of looking around, not so constantly moving between perches, and making larger jumps between perches, 3′ common. Later, another association of chickadees, golden-crowned kinglets and a white-breasted nuthatch. These mixed flocks stand out because after going through a long segment of forest path where there are essentially no birds, suddenly there are many at once of several species. Again, chickadees sitting longer in one place and moving farther between perches. All moving together in same direction through forest, and moved away from me as I observed them. Later still, a couple of chickadees without associates. Perhaps this is the kind of observation that led to the local core species idea.

25JE00. This spring I have observed 3 chickadee groups with parents and fledglings, one at the Arboretum on 1JE, one yesterday at Willowbrook, and a third in another part of the Arboretum today. Instead of being spread out, in each case the groups were clustered in a small area no more than 20 feet in diameter, and they moved only very slowly. Feedings were frequent, so apparently the parents directed or led their young to food-rich locations.

11MR01. A chickadee at Timber Ridge Forest Preserve with a variation on the fee-bee song: the “bee” syllable is repeated, and each syllable has the usual hinged quality, i.e., “fee-bee-ee-bee-ee.”

More recent observations have focused on the role of black-capped chickadees in mixed flocks.

29AU01. Algonquin Park, Ontario, Mizzy Lake Trail. Flock 1: Golden-crowned kinglets, a young-of-the-year black-throated green warbler, black-and-white warbler, black-capped chickadees. Flock 2: At an edge between mixed forest and a lake. Black-capped chickadees, several black-throated green warblers (appear to be sticking together to form their own group within the flock), at least 1 blue-headed vireo, 1 female or young blackburnian warbler, 1 chestnut-sided warbler, and 1 Tennessee warbler. The black-capped chickadees are very abundant here, the most apparently numerous birds in the forest (because of their frequent calling and frequent presence). It is easy to see how migrant birds accustomed to forming mixed flocks with them here in the north could attach to resident birds they encounter on the trip south. Flock 3: Black-capped chickadees, Swainson’s thrush.

30AU01. Algonquin Park, Bat Lake Trail. Flock 1: Black-capped chickadees, a black-and-white warbler, the latter singing. Flock 2: Black-capped chickadees, red-breasted nuthatches, golden-crowned kinglets, 1 or 2 black-throated blue warblers, at least 1 Tennessee warbler, yellow-rumped warbler. The first three species are the vocal ones. These flocks are distinctive: you go for hundreds of yards seeing or hearing no small birds, then suddenly there is one of these diverse groups in a small area.

31AU01. Algonquin Park, Spruce Bog Trail. Flock 1: Yellow-rumped warblers, black-capped chickadees, red-breasted nuthatches, golden-crowned kinglets. Do more northern birds, living in more open forests, either not have chickadees to associate with, or perhaps the scattered trees (if they are) remove the advantages of mixed flocks? See if it’s true that the non-mixed-flock species tend to be more northern.

12SE01. Willowbrook. Flock 1 around west end of cross trail. 2 chickadees and 1@ of black-throated green, magnolia, Tennessee (sang a couple times), and 1 unidentified species. Flock 2 near the NW corner of nature trail, a magnolia warbler apparently alone.

13SE01. Willowbrook. A large but difficult to view mixed flock near office building: 3 chickadees, 2 redstarts, a blackpoll warbler, a red-breasted nuthatch, and many others.

14SE01. Willowbrook. Flock 1 around NW corner of nature trail: redstart, chickadee, downy woodpecker, Tennessee warbler, black-throated green warbler, magnolia warbler, red-eyed vireo. Flock 2 between eastern part of animal exhibit and bridge. Chickadee, 3 redstarts, downy woodpecker, blackpoll warbler (it is possible that the one seen earlier joined this flock; it was near this location).

17SE01. Willowbrook. Flock 1: 3 chickadees, 1 redstart, others perhaps; near west end cross trail. Flock 2, base of savanna, 2 palm warblers only. Flock 3, brush area east of Nature Trail, 2 chickadees only. Flock 4, another part of same brush area, 2 chickadees, a magnolia warbler, 1 other unidentified.

19SE01. Willowbrook. Flock 1, east exhibit area to bridge: 2 chickadees, 1 black-throated blue warbler, 1 redstart, possibly others. Flock 2, west end cross trail: staying around berry-feeding robins, waxwings and catbird, with no chickadees around: a black-and-white warbler, 2 downy woodpeckers, a redstart, a blackpoll warbler, possibly others.

25SE01. Elsen’s Hill, plateau above river. Flock 1: at least 8 vocal, active yellow-rumped warblers, and a ruby-crowned kinglet. Flock 2, very large and diverse, only some individuals identified: 2 chickadees, black-throated green warbler, blackpoll warbler, 2 Nashville warblers (1 low in an aster thicket another in low tree branches), downy woodpeckers, a parula behaving like the Nashville, 2 redstarts, a chestnut-sided warbler.

26SE01. Willowbrook, between bridge and animal exhibit. 2 chickadees, and at least one @ of vireos (Philadelphia, red-eyed, yellow-throated), warblers (Tennessee, magnolia, parula, black-throated green), scarlet tanager, red-breasted nuthatch.

27SE01. Willowbrook. Flock between bridge and exhibit fence. 2 chickadees, 1 Tennessee and 1 magnolia warbler.

30SE01. Fox River and Island Park, Batavia. Many yellow-rumped warblers spread out all over, some hover-gleaning, some flycatching, others reaching for poison ivy berries. With them, a chickadee, a male Cape May warbler in the top of a silver maple, very active in the short time I saw it.

14SE02. Elsen’s Hill. I walked for several minutes, seeing apparently independent Tennessee warblers (2 together) and a Nashville warbler before encountering a large flock. This flock seemed to be changing composition over time, i.e., after my initial observations I walked a short distance away, then returned, and when I came back, some birds were the same but there were several new ones, as well. Later, after following the flock for 50 minutes or so and losing them in a direction I did not want to pursue in the brush, I returned to the starting point and a small mixed flock was there, with some of the birds I saw initially (apparently, none were marked of course) and a couple added ones. Initial group: a blackpoll warbler, 2 red-eyed vireos, 2 redstarts, an essentially silent chickadee, a black and white warbler, a Tennessee warbler, a Swainson’s thrush, a female or young black-throated blue warbler that was the only flock member calling consistently, all foraging in brush understory within 15 feet of the ground (the redstarts were the only ones consistently going above 10 feet; this was after 9 a.m.). Flock after my return: golden-winged warbler (like the redstarts, up higher, and very active, including flush and pursuit), a male and 2 female or young black-throated blue warblers, 2 Tennessee warblers, a black-throated green warbler, 3 redstarts, 2 blackpoll warblers, a black and white warbler, a blackburnian warbler. After it had warmed up some, later, a magnolia warbler foraging 20-25 feet up and the other birds also have gone higher. Doing a lot of reaching, and spending much time looking from each perch. At 10:45 I returned to the starting point: 4 noisier chickadees, 2 red-eyed vireos, a blackpoll warbler, a male redstart, a magnolia warbler, all except the chickadees foraging higher, throughout the tree canopies. Also a downy woodpecker, black-throated green warbler, Swainson’s thrush.

25AU08. Fullersburg Woods. First mixed flock of the fall migration has 2 chickadees, a downy woodpecker, a Tennessee warbler and a Canada warbler.

28AU08. Fullersburg Woods. Mixed flock just S of Willow Island bridge: 2 chickadees, 2 Tennessee warblers, 2 magnolia warblers, a gnatcatcher.

29AU08. Fullersburg Woods. Mixed flocks: One with four chickadees, two Tennessee warblers, a magnolia warbler and a black-and-white warbler. Also, 2 Tennessee warblers together apart from mixed flock. At mid-day a mixed flock near the junction of trails with 3 chickadees, 3 Tennessee warblers, a white-breasted nuthatch, a magnolia warbler, a parula. Chickadees were doing a lot of hanging upside down, Tennessees less acrobatic running along tops of branches and reaching, magnolia and parula more rapid movements, hopping between branches, nuthatch on bark, all in top half of canopy.

13SE08. Kettle Lakes Provincial Park, Ontario. Large, mixed flock in an area around 75 yards in diameter: at least 2 black-capped chickadees, 5 golden-crowned and 4 ruby-crowned kinglets, 4 yellow-rumped warblers, 2 red-eyed vireos, downy woodpecker, black-and-white warbler, black-throated green warbler, redstart, red-breasted nuthatch. I’m hearing white-throated sparrows, but they seem all near the ground rather than up in the trees with the others. Weak songs from ruby-crowneds, the black-throated green and the black-and-white. This is mainly an area of aspens with some jack pines. Mixed flock: at least 2 chickadees, at least 2 golden-crowned kinglets, 2 ruby-crowned, and a yellow-rump. Aspen grove again with some jack pines and a couple white pines.

15SE08. Nagagamisis Provincial Park. On trails, encountered a little flock of at least 7 ruby-crowned kinglets. Nothing up with them first time through, but white-throated sparrows lower down in that area (on the way back a chickadee, a brown creeper, 3 golden-crowned kinglets and a Swainson’s thrush added). Birds have been few, and I cannot discount the possibility of an association of the white-throated sparrows with this group. On the Time Trail, balsam fir the dominant tree with plenty of white spruces, some black spruces, white cedars, paper birches. Another mixed flock with at least one chickadee, 2 ruby-crowns, 3 golden-crowns.

21SE. Mayslake. A mixed flock at edge of Area 9 and grounds containing a black-throated blue warbler (new preserve species), black-throated green, 2 redstarts, 2 blackpolls, chestnut-sided, Nashville, black-and-white, magnolia, and a chickadee.

The Grebe and the Mallards

by Carl Strang

For more than a week, a migrating pied-billed grebe stayed on May’s Lake in late November.

This bird was constantly in the company of a group of mallards. Even when the ducks were standing on fallen logs near shore, the little diving bird floated close by. Here the grebe is at the far edge of a feeding mallard group.

The ducks were diving for aquatic plants. Mallards are not very good divers. The splash in the following photo is characteristic of their inefficient plunges.

They stayed beneath the surface 3-5 seconds, which in the relatively shallow water was enough for them to acquire a snack. If I were a children’s book author, I might be inspired to write a story about how the grebe was lonely, made friends with the ducks, then taught them how to dive for food in exchange for their companionship. While that story has emotional appeal, I’m pretty sure none of it was taking place.

Notice how two of the mallards are taking a peek below the surface before diving. The area where they are feeding is only a little farther out from depths where they can get food by tipping up. Mallards don’t dive often, but do so occasionally when bathing or when chasing one another. I’m pretty sure the ducks would be diving for food even if the grebe weren’t with them.

So what of the grebe’s behavior? This is a fairly solitary species, except during the breeding season. They don’t travel in flocks, or even family groups. Young make their way south on their own, entirely by instinct. Nevertheless, a grebe wanting others to hang out with could find them, and wouldn’t need to affiliate with ducks (grebes are now known to be more closely related to flamingos than to ducks, thanks to genetic comparisons made at the Field Museum).

Pied-billed grebes frequently can be seen in the vicinity of flocks of diving ducks or coots on larger lakes during migration, and my impression is that this is more than a random association, though some grebes also are off by themselves. I think the affiliation probably is more like what we see in mixed flocks of migrant songbirds than a social expression. There is evidence that mixed flocks have two advantages for their members. First, they provide more sets of senses for detecting the approach of predators (and the lucky bird that first spots such an approach can place itself on the far side of the flock). Second, the activity of so many birds foraging in close proximity stirs up prey which may escape the individual that first flushed it, but then can be caught by one of the others. It seems likely to me that something like this is going on with the grebes, too.

Mixed Flocks

by Carl Strang

 

Yesterday at Mayslake I saw 15 juncos, 2 song sparrows, 3 downy woodpeckers, a goldfinch and a white-breasted nuthatch apparently moving together as a mixed flock. I’m more accustomed to seeing such behavior in the fall, so today I want to provide some background for this phenomenon.

 

 

 

At the September peak of the fall songbird migration, I have found that the quickest way to the greatest diversity of warblers and other migrants is to listen for the chickadees.

 

chickadee-1b

 

Black-capped chickadees are on the verge of forming their winter flocks and are very vocal at that time of year. From the standpoint of a naïve migrant, tired and hungry from the night’s migratory jump south, the chickadees represent a familiar bit of normalcy in an unfamiliar location.

 

Yes, I know, I’m projecting human emotions onto distinctly non-human animals that in fact are closer to dinosaurs than to us. But hear me out. I’ve gone north in the late summer and early fall, and I have seen how the black-capped chickadees up in Canada attract other birds to them like dung beetles to, well, dung. Chickadees are active and vocal, easy to find in the quiet autumn forests. Other birds easily can keep track of where the flock is going just by following the chickadees. When the migrants drop down out of the sky at dawn they are entering unfamiliar territory. Where’s the food? Where do the local predators hang out? The chickadees know. They are in the area year ‘round. They are active, vocal, and easy to follow.

 

chickadee-2b

 

There is evidence in the scientific literature supporting both predator avoidance (lots of eyes and ears on the watch, also the ability to hide in the flock) and improvement in individual foraging efficiency (for instance, one bird may catch an insect that is flushed by another) as reasons why mixed flocks form. I see no reason why both advantages can’t play a role, perhaps with different importance at different times.

 

I have thought that it would be an interesting inquiry to see if there are consistent patterns in the structure of mixed flocks. Patterns could be spatial, with different species or individuals holding consistent places within the arrangement of the individuals of the moving flock. There could be rules governing the number of species, number of individuals, or distribution of individuals among species. But so far, I just have some partial counts of the members of a few mixed flocks.

 

How to collect the data? In September the trees still are fully in leaf, and it’s a challenge just to find all the members of a flock let alone keep track of them all. But it’s fun to find the flocks and tally their members, keeping alert to possibilities, hoping a hint of a pattern might show itself.

 

Here are just a few examples of flocks I’ve seen:

 

  1. Algonquin Park, Ontario, Mizzy Lake Trail, 29 August 2001, at an edge between mixed forest and a lake. Black-capped chickadees, several black-throated green warblers (appear to be sticking together to form their own group within the flock), at least 1 blue-headed vireo, 1 female or young blackburnian warbler, 1 chestnut-sided warbler, and 1 Tennessee warbler.
  2. Algonquin Park, Bat Lake Trail, 30 August 2001. Black-capped chickadees, red-breasted nuthatches, golden-crowned kinglets, 1 or 2 black-throated blue warblers, at least 1 Tennessee warbler, yellow-rumped warbler. The first three species are the vocal ones. These flocks are distinctive: you go for hundreds of yards seeing or hearing no small birds, then suddenly there is one of these diverse groups in a small area.

 

Golden-crowned Kinglet

Golden-crowned Kinglet

 

 

 

  1. West DuPage Woods Forest Preserve, West Chicago, Illinois, 7 May 2000. Several blackpolls in a mixed flock with yellow-rumps, chestnut-sideds, a golden-winged, a blue-winged, some Tennessees, a couple black-and-white warblers, several scarlet tanagers and rose-breasted grosbeaks of both genders, a Swainson’s thrush or two, a couple indigo buntings. No chickadees in this flock, but in spring migration many birds are singing so flock cohesion is easier.
  2. First mixed flock of the 2008 fall migration observed at Fullersburg Woods, Oak Brook, Illinois, on 25 August has 2 chickadees, a downy woodpecker, a Tennessee warbler and a Canada warbler.
  3. Fullersburg, 29 August 2008, a mixed flock with 3 chickadees, 3 Tennessee warblers, a white-breasted nuthatch, a magnolia warbler, a parula. Chickadees were doing a lot of hanging upside down, Tennessees less acrobatic running along tops of branches and reaching, magnolia and parula more rapid movements, hopping between branches, nuthatch on bark, all in top half of canopy.
  4.  Kettle Lakes Provincial Park, Ontario, 13 September 2008. Large mixed flock in an area around 75 yards in diameter: at least 2 black-capped chickadees, 5 golden-crowned and 4 ruby-crowned kinglets, 4 yellow-rumped warblers, 2 red-eyed vireos, downy woodpecker, black-and-white warbler, black-throated green warbler, redstart, red-breasted nuthatch. I’m hearing white-throated sparrows, but they seem all near the ground rather than up in the trees with the others. Weak songs from ruby-crowneds, the black-throated green and the black-and-white. This is mainly an area of aspens with some jack pines.

 

Clearly there are many species that can be found in these mixed flocks, and resident birds like downy woodpeckers and white-breasted nuthatches are common members. Descriptions like these are the only data I have so far, but it’s fun just to find the flocks and try to account for all their members. Maybe some day a pattern will show itself.

 

 

 

For now, I’ve got yesterday’s mixed flock to ponder. No chickadees were present, but with the vegetation open, now that leaves have dropped, maintaining visual contact is easier especially with so many individual birds involved. Yet another observation for my growing files on the subject.