Sunday, January 29, 2012

Red-breasted Satellites

While hiking at the MacCready Reserve in southern Jackson County a few weeks ago, I heard what I was pretty sure was a White-winged Crossbill fly over me twice, but subsequent attempts to find the bird (or the flock that it was hanging out with) were unsuccessful.  This Friday, Don and Robyn Henise found a small flock of crossbills at MacCready, so this morning I went out to try and make up for my missed opportunity to record crossbills last weekend in Washtenaw County.

To make a long and disappointing story short, I found no crossbills, though Craig Robson and Heidi Doman did have a single bird fly over just prior to my arrival.  We also found evidence of recent crossbill activity, such as bits of tamarack cones on top of the snow (indicating very recent activity, given the snow accumulation today) and mangled Norway Spruce cones.

After parting ways with Heidi and Craig, I stirred up a mixed flock of birds in a transitional area between a small spruce stand and the red pines that dominate the majority of the reserve.  I actually got the attention of the birds by playing a White-winged Crossbill recording, which prompted a single Red-breasted Nuthatch to call.

Instantly, the calling of the nuthatch prompted a mob of chickadees, a few Blue Jays, a couple of White-breasted Nuthatches, and a Downy Woodpecker to swoop down and begin mobbing me.  I had hoped to record the entire succession of the encounter to illustrate some of the dynamics of mixed species flocks.  Unfortunately, in addition to having a dead camera battery, my recorder was having problems with the memory card, allowing me to make only brief bits of recordings as the scene unfolded.  I would later find a single Ruby-crowned Kinglet in this flock, which really got me down about my camera being MIA, given the rarity of this species this far north during the winter.

During the winter in temperate North America, chickadees, nuthatches, kinglets, woodpeckers and a few other species (e.g. Brown Creepers) aggregate in small flocks that travel and forage together.  This is thought to be a strategy that is selected for based on the benefits individual flock members can accrue, such as increased foraging efficiency, reduced risk of predation, and reduced vigilance that is required from each individual to detect predators (Sullivan 1984, Dolby and Grubb Jr. 1998).

What I find particularly interesting is the fact that the two groups of birds that are almost always found in these flocks (Parids and Sittids) have distinct functional roles within the flock during a predatory encounter -- roles that reflect the differences in the ecology of the two groups.  Nuthatches are primarily bark-foragers that are usually found high in trees, while chickadees and titmice tend to forage lower in the canopy and can be found foraging in shrubs, on tree branches, the ground, and even the bark of trees.  These differences are maintained in mixed flocks and have given rise to the terms satellite and nuclear species, respectively, to describe the spatial relations of these two groups.  This concept is not restricted to temperate North America, and species in a variety of ecosystems at (almost) all latitudes engage in similar relationships.

Depending on where a potential predator is approaching a mixed flock from, either group might be more likely to alert other members of the flock with an alarm call.  I've often noticed that when a hawk flies over or I approach a flock of birds from a distance in an open area, nuthatches and woodpeckers are usually the ones to expose my whereabouts.  Conversely, many a time I've watched Snapper wander into a patch of thick bushes, rousing the suspicions of chickadees and titmice.  This fits well with the available literature, which indicates that nuclear species are more likely to detect terrestrial predators in low-visibility situations, whereas satellite species are likely to detect aerial predators approaching the flock from a distance.

I actually did a little project on mixed flocks for an independent study last year.  Specifically, I was interested in finding out if there are any key parameters of alarm calls that birds might hone-in on to assess the level of a threat.  In order to investigate this, I altered different parameters of a White-breasted Nuthatch alarm call that I recorded at Dahlem last winter and conducted playback experiments to birds in the field.  In short, I found that increasing the amount of time between notes (by 4/10 sec.) and increasing the length of the notes themselves (by 5/100 sec.) significantly altered antipredatory responses of birds.  I really have no intentions of publishing any of these data, so below are barplots depicting these results.

The responses on the x-axis are categorical responses, meaning there is no 'order' as you increase or decrease the value.  "0" denotes no apparent antipredatory response, "1" denotes a "freezing" behavior that I usually observed when birds were already in an area with sufficient cover, and "2" denotes a bird immediately fleeing to bushes or other forms of cover.  The trend for the second plot is at least intuitively easy to explain (insert multiple caveats), but I'm still a bit puzzled by the results from the first.  Much to my delight, Ellis (2007) found very similar results when investigating key parameters of alarm calls in White-throated Magpie-Jays, which just might spur me to redesign my study and have another go at publishing the results.

In highly unrelated news, I think it's worth mentioning that the trails at MacCready today were absolutely covered with Snow Fleas (Collembola), which seemed unusual given the relatively cool temperatures and overcast skies this morning.  My only guess is that they might have emerged in large numbers yesterday during the sunny afternoon.  I wonder if the extreme day-to-day variation in weather that we're seeing this winter will have any effect on these hardy little beasts.  Oh, and I also saw quite a few Skunk Cabbage peaking through the snow!

Dolby, A.S., Grubb, jr T.C. 1998. Benefits to Satellite Members in Mixed-Species Foraging Groups: An Experimental Analysis. Animal Behavior. 56(2): 501-509.
Ellis, J.M.S. 2007. Which Call Parameters Signal Threat to Conspecifics in White-Throated Magpie-Jay Mobbing Calls? Ethology. 114(2): 154-163.
Sullivan, K.A. 1984. Information Exploitation by Downy Woodpeckers in Mixed-Species Flocks. Behaviour. 91(4): 294-311.

Saturday, January 21, 2012

Crossbills and Butterbutts

Much to the neglect of my neurobiology homework, I opted to chase a large flock of White-winged Crossbills reported a few days ago from Park Lyndon North in Washtenaw County.  Reports of large crossbill flocks were abundant from the Upper Peninsula early this winter, giving me hope that a few might wander into southern Michigan this year.

Yellow-rumped Warbler

Immediately after stepping out of my car, I saw a sizeable flock of birds foraging low in a shrubby edge to a pretty steep hill covered in deciduous trees.  To my delight, the majority of the birds turned out to be Yellow-rumped Warblers!  Dan Sparks-Jackson has reported a few hanging out in this area for a few weeks now, so I wasn't entirely surprised to see and hear them 'cheking' away.

Berry wars!

These birds seemed to be doing a lot of foraging on a patch of poison ivy berries, but I also noticed a blue-colored berry of some sort in the bill of the bird in the first picture (also pictured just above).  If you have any idea what it might be, I'd love to hear from you!  The flock of at least 9 birds was associating with a few Eastern Bluebirds, a Downy Woodpecker, and a White-breasted Nuthatch and spent the majority of their time right on the edge, which was receiving a lot of sun (which felt great to me as well!).  As of late, I've been collecting data on overwintering Yellow-rumped Warblers in central and southern Michigan as a part of a little personal project aimed at documenting habitat selection by overwintering butterbutts.  So far, it seems that areas around small, wooded streams with shrubs and poison ivy berries are the preferred environments of this hardy warbler.  This particular spot is a bit of an oddity as, for all I could tell, there is no nearby water.

And to think, come May, no one will care

After a bit of a walk that yielded little else in the way of birds, I found myself in the tamarack swamp that the crossbills had been spotted in.  While the cone crop was very good here, nothing was seen or heard for around an hour.  Even when the silence was eventually broken, it was only done so by a single female/juvenile crossbill that flew briefly over the swamp.  Eventually this bird returned for a few minutes, affording long looks at little more than a silhouette feeding on tamarack seeds.


After a couple hours of patiently waiting with little more than distant call notes and chatter, many of the 10 or so birders that had gathered in the area left rather disappointed.  On their way out, however, a pair of birders spotted 5 or so crossbills and called the rest of us over.


As we marveled at the chromatic brilliance of the adult male pictured above, it soon became apparent that there were many more birds.


Birds continued to congegrate in the same tree, seemingly coming out of hiding from every possible direction.  The highest count anybody managed was somewhere around 40 individuals.  Unfortunately, malfunctioning recording equipment (i.e. me forgetting to replace the batteries) prevented me from recording the incredible diversity of vocalizations produced by this flock, not to mention the surprisingly audible tune of tamaracks getting pwned in an evolutionary arms race.  Disappointing as that may be, my incompetence did allow me to focus all of my attention on photographing crossbills, which is never a bad way to end an afternoon.

Interestingly, I noticed that the birds would often forage in trees that had far less cones than others mere feet away, but that the preferred trees were less cluttered than the others both in terms of branches and vegetation structure and proximity to other trees.  A fellow birder celebrating his life White-winged Crossbills and I speculated that these 'more open' trees might be preferred for detecting/evading aerial predators.

The northern skies were good to me today, even if they did not deliver the spectacle of charged solar particles that I was hoping to marvel at tonight.

Friday, January 13, 2012

Thursday, January 12, 2012

Monday, January 9, 2012

Bananas and Peanut Butter

So the title is a bit of a digression from the usual content of this blog.  Classes started today, meaning I'm a bit short on sleep and enthusiasm.  This is not to say, however, that the sweet and salty title of this post has no relevance to my experiences in nature.  Indeed, as a generally poor manager of time, I often find myself without any time for the trivial pursuit of adequate nutrition (this is especially true when birds are involved).  For this reason, this quick, protein- and carbohydrate-rich snack has fueled the wanderings that are the basis for many of my posts.  Long may it be so (though climate change may have other plans).  If the demise of the bastardized remnants of Hawaii's avifauna, the integrity of the boreal forest, and the salinity of the oceans are not enough to prompt our country to action, then perhaps the loss of PB&J will.

A future relict snack?

On a lighter note (sort of), last week was my final week of winter break, which I usually spend sulking around my house in despair over the days to come, when birds and sunlight are but distant memories of life in the 'before time'.  This year I opted to change this depressing pattern, even if it meant simply getting out of the house in search of birds that I had little chance of finding.

First winter White-throated Sparrow

Inspired by my luck on the Waterloo Christmas Count and Joyce Peterson's find on the Albion Christmas Count, I started out the week searching for Yellow-rumped Warblers in Jackson County.  Based on observations of this species in southern and central Michigan during this winter, it appears that they tend to prefer shrubby, riparian areas with a good supply of berries (particularly poison ivy) and open water.  As luck would have it, such habitat exists mere minutes from my house at Ella Sharp Park.  But despite perfect habitat, I came up empty on butterbutts, though the place was loaded with White-throated Sparrows, which I haven't been able to find anywhere else in the county.

Adult, (putative) tan-striped morph

Within the four or five flocks I encountered, I only saw a couple of white-striped individuals, which seemed odd (though many may have been first year birds that simply haven't molted yet).  White-throated Sparrows exhibit a polymorphism that shows variation in morphometrics, behavior, and, most noticeaby, plumage (specifically in the crown stripes) (Lowther 1961).  Interestingly, this polymorphism has been linked to a very large inversion on the second chromosome that contains about 1,000 genes (Thorneycroft 1966).  Because inversions suppress crossing over (review your meiosis!), this means that the genes within the inversions that 'cause' the different morphs never get mixed together, allowing these sections of the genome to diverge from each other.  What's perhaps even more interesting is that individuals of this species almost always mate with an individual of the opposite morph (Falls & Kopachena 2010), a behavior that may be influenced by this very region of the genome.  Because of this, both morphs are stably maintained within the species and speciation has not occurred, even though this large area of the genome is diverging.  When you consider that this inversion is thought to have occurred around 2.2 million years ago (Thomas et al., 2008), and that it causes many substantial differences in behavior and morphology, it is easy to imagine that, without this quirk of mating behavior (disassortative mating), we might very well have had another Zonotrichia species in North America!  Science is fascinating.

Field Sparrow

After failing to find a butterbutt and having my camera die just before finding a huge flock of American Robins and a Hermit Thrush, I headed home to recharge my spirits and batteries before heading out again, this time with a more realistic goal -- Swamp Sparrows.  I don't know that I'd ever seen a Swamp Sparrow in the winter, though I certainly know they're around in small numbers.  I opted to first look in an area where flooded hardwoods borders cattail marsh near my home, which has been good for sparrows in past years.  Much to my surprise, the Field Sparrow pictured above was the first sparrow I saw.  I assume this is probably a bird from the consistent flock I've posted about previously, given the close proximity between locations.  Interestingly, while the flock is incredibly skittish and difficult to observe in the nearby meadow, this bird was foraging on Reed Canary Grass (I think?) seeds just a few feet from me, paying almost no mind to my phishing efforts directed at his (her?) evolutionary cousins.  This seemed like curiously bold behavior, given that this individual was apparently not in the company of any other birds.

Song Sparrow

No sooner had I forgone my efforts to stir up any other birds when this Song Sparrow and two others started cheking away at me, all while skillfully managing to prevent any decent photographs from happening on their behalf.  Curiously enough, it appeared that the Field Sparrow did react to the calls of the Song Sparrows by taking evasive action into thick shrubs.

Swamp Sparrow

With all sparrows out of sight, I decided to play a few chip notes from a Swamp Sparrow, just to see if one was lurking in the cattails.  Five seconds of the clip hadn't yet passed when this individual sprang up from a patch of grass, chipping away at my iPhone with the exact same calls that I was broadcasting.  I don't know that I'd ever noticed it before, but it appears that Swamp Sparrows have much thinner bills than Song Sparrows.  Interesting.

American Tree Sparrow

Just before I decided to head home, a flock of about ten American Tree Sparrows came dashing into the area and immediately took to foraging all over the place, including on the ice.  A few minutes after the cheerful, metallic chip notes of this flock had been bouncing all over the place, the Song Sparrows and Field Sparrow came out of hiding and joined the group in foraging on top of logs and in grassy patches around tree trunks, though they never strayed far from cover unlike the bold denizens of the Canadian tundra (perhaps a name change is in order).

I originally intended to add details about another unsuccessful warbler quest (this time for Common Yellowthroats), but realized that it would amount to little more than me continuing on about sparrow behavior.  In an attempt to keep you from not ever wanting to look at future posts containing sparrows, I'll just post a few pictures from the day.

One of about ten at Cascades Park

One of about five

How can you not adore chickadees?

...I mean, seriously.

One of many!

Blue Jay

Eastern Bluebird

One of at least six on the Hoffman Trail

Is there a better looking woodpecker in the eastern forest?


Falls, J. B. and J. G. Kopachena. 2010. White-throated Sparrow (Zonotrichia albicollis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: