7/30/12
In terms of species, we are still on the downward
slope from week to week with the "bottom of the
abyss" coming in week 33, arguably the most
difficult walk of the year. Typically, this
means that the temperatures and/or humidity are
high and even the summer residents are trying not
to move around too much at noon. We lose our
mallards in August and the house wrens are gone.
Yellow-rumped warblers are a distant memory and
the latency of their return is still a couple of
months away. We have, however, been having a
mild summer, so there is some reason to hope that
next week's record of 15 and the following week's
nadir of 14 species are at risk. After week 33,
record numbers start to climb as we move towards
the Fall migration for most species and we have
an ever improving set of opportunities to
sidestep a heat wave. That's enough future
speak. If we consider the present in the context
of the comparable past, we do quite well. On one
level, it would have been nice to take the record
but I must admit that I would actually have been
sorry to see it. The longest standing record in
the Caltech birding walk is for week 31. In
1988, we saw (or at least Alan did), 17 species.
This record still stands but we have the tangency
of our own glory for 2012 with a species count of
17. We have tied the record for week 31.
See the plots at
http://birdwalks.caltech.edu/bird_data/species_time.html
and
http://birdwalks.caltech.edu/bird_data/two_plots.htm
Now, 17 is not a lot of bird species, even by
Caltech standards but my view is that this over
attention to high numbers is missing a key point.
If you are thinking about learning a little bird
identification, summer is the best time of the
year to get started in southern California. In
your neighborhood, you probably don't have to
deal with more than a couple dozen species and,
probably only a handful of regular callers.
Think of them as your Berlitz to birding. They
are the foundation. Get these locked in and you
will have an ability to recognize the oddities of
Fall migrators as they arrive. Summer also
brings an opportunity to appreciate the finer
details of behavior for your summer residents.
You know (or will know) what the bird is. Now, you
can pause to appreciate. The game isn't over
just because you know that the backyard
flycatcher in a tux is a black phoebe. You will
notice that he has favored perches. Does he use
them systematically or at random? Does he have a
schedule? Does he avoid or spit out certain
flying insects? Does he tolerate other black
phoebes? If he roosts in your back yard, when
does he get up in the morning and when does he go
to bed? If your hearing is not so deprived as
mine, you should be able to detect his calls.
Does he call in flight or on perch, as soon as he
lands, or just before lifting off; or is it after
catching an insect? These are all questions you
can answer if you don't stop looking at or
listening to your bird immediately after the
words "black phoebe" passed through your mind.
It need never get old. Last Tuesday, I was
walking by the rose planter near Millikan's head
and noticed a black phoebe perched on its lip.
Now, we have a resident black phoebe that owns
the entire area immediately surrounding Millikan
library and I thought nothing of it. However, I
then notice a second phoebe come into land on a
Jacaranda twig. This was unusual and I stopped.
I don't think I've ever seen multiple black
phoebes in this area outside the breeding season.
Up to this point, the resident had either not
seen or had not deigned to notice the new bird
but when this bird leaps off the Jacaranda perch
to chase an insect near the planter, there is no
mistaking intent and no ambiguity that we have an
interloper intent on catching the resident's
insects. Our resident lifts off and flies, not
at the insect, which was within easy reach, and
which all three of us could see, but straight at
the new bird. The new bird banks and makes as
sharp turn towards me, only a meter or so away,
he banks again. The resident is on his tail, not
more than a body length behind and I hear what I
can only describe as a tiny scream. I don't know
whose vocal expression this was but I can say
that it is the first time I have heard a black
phoebe. The new bird continues flying as fast as
he can and lands on the root ball of a jacaranda;
the resident returns to the rose planter. After
a few seconds, the resident decides to fly
directly at the new bird. He is not moving as
fast as he was the first time but this is clearly
a formal challenge and the new bird has had
enough. He quits the field and flies away, out
of my field of view. Our resident, having
defended his territorial integrity, returns to
the planter. The insect that started this tete a
tete is nowhere to be seen. I was reminded of an
old General Schwarzkopf briefing in which he
showed "the luckiest man in Iraq". The man is a
truck driver who is driving onto a bridge just as
allied missiles that aren't waiting for anybody,
strike the bridge immediately in front of and in
back of him. He stops the truck and gets out.
He is still alive. He is incredibly lucky. I
was lucky.
It seemed like there should have been some
excellent thermals rising during the walk but we
saw only one raptor, naturally a Viveca capture.
It was probably a Cooper's hawk, although too far
off to be sure. Cooper's hawks used to be
exclusively migrators, wintering in southern
California and migrating north to breed but, in
recent decades, some Cooper's have decided to
stick to the southland and become year-round
residents (most of them still migrate north in
the Spring). This is a testament to our strong
support of urban prey species.
The hummingbird feeder house outside Tournament
Park yielded several Selasphorus hummingbirds and
a couple of black-chinneds, leading to another three
hummingbird day. The black-chinned hummingbirds
are getting ready to head back to Mexico, where
they winter, but we should still have a good shot
at them over the next couple of weeks.
We came to the Bewick's wren territory just west
of the hummingbird house and Alan tried a song
sparrow song on his iPhone; Bewick's wrens are
known to have an antagonistic relationship with
this species because, during the breeding season,
song sparrows actively forage for insects for
their young, the same insects that the Bewick's
wants for himself. He gets no response.
Perhaps, this bird never had his lunch stolen by
a sparrow. Alan tries a western Bewick's wren
song for good measure. No response. We start to
leave but, before we get up a full head of steam,
the Bewick's wren pops out and berates Alan,
following him for several meters just to make
sure that he understands whose territory this is.
Alan seemed oblivious, perhaps because he knew
that he was safely in the neutral zone of the
driveway but had he been a wren, I'm sure that he
would have been seriously intimidated.
The end began with the shadow of a butterfly,
which led to looking up and seeing lots of
bushtits, which led to seeing a larger bird to
the right. It has a pale yellow belly and a
russet tail. It acts like a flycatcher. It is a
flycatcher. We have an ash-throated flycatcher.
They pass by us heading north for several weeks
centered around week 21 and then dribble past us
going south between weeks 30 and 38. So, this
sighting fits right in and is a fitting end to a
record-tying day.
The date: 7/30/2012
The week number: 31
The walk number: 1154
The weather: 82 F, sunny
The walkers: Alan Cummings, Viveca Sapin-Areeda,
John Beckett, Kent Potter, Vicky Brennan
The birds (17):
Mourning Dove
House Finch
Anna's Hummingbird
Acorn Woodpecker
American Crow
Mallard
Bushtits
Black Phoebe
Hummingbird, Selasphorus
Lesser Goldfinch
Red-masked Parakeet
Black-chinned Hummingbird
Bewick's Wren
Hawk, Species
Yellow-chevroned Parakeet
Ash-throated Flycatcher
Swallow, Species
--- John Beckett
Respectfully submitted,
Alan Cummings
8/3/12
http://birdwalks.caltech.edu/index.html
7/23/12
Sometimes the beginning tells the tale. Kent had
a productive pre-walk stroll to the starting
point, picking up the mallard, who seems to have
molted her entire tail, and a pair of rock
pigeons lounging around on the roof of Arms (at
least that's where they were when Vicky and I
passed by a minute or two later). If that had
happened last week, we would have tied the record
for week 29. Unfortunately for us, this was week
30 and the record was a much sturdier 19.
Although we welcomed the pigeons, they were
flirts at the party, helping us taking us to a
view overlooking the promised land. We could
look but we could not kiss the ground and we
could not surpass. Our species count for the day
ended at 17, which is still well above the median
(13) and low (9) for week 30.
See the plots at
http://birdwalks.caltech.edu/bird_data/species_time.html
and
http://birdwalks.caltech.edu/bird_data/two_plots.htm
So, there is little cause for complaint and the temperature,
although mildly toasty, was not oppressive. My
usual test for deciding whether or not to call a
walk hot lies in watching Alan working the
shadows. If he is hopping from shade to shade,
it's a hot day. There was no hopping today.
I saw Kent all by himself at the walk starting
point at 11:58 but Vicky, whom I had intersected
along the way, and I decided to see if the
mallard was present before joining him. She was.
This would still have made the starting gate on
time but we got sidetracked trying to turn a
hummingbird species into something specific. We
managed to get there (Selasphorus) but only at
the cost of being a couple of minutes late.
The Maintenance yard is often open but it is also
gated with a multiple lock system that is
designed to allow anyone with one of the several
different keys to get into the yard. If the gate
is properly locked, it is not difficult to get
in, provided you have one of the designated keys,
something Alan has. Unfortunately, it is also
possible to lock the gate so that only one key
can open it up, which is what happened. We
didn't have the magic key and nobody except I was
up for a keyless entry. It must have something
to do with that horse thief ancestor of mine. He
obviously managed to pass some genetic material
my way before getting hanged.
Morrisroe brought a couple of interesting events.
We had several red masked parakeets crunching
nuts in a tree, aware of us a few meters away but
uncaring. This led to some great views for both
species. More unusual was Viveca's discovery of
the bottom portion of what appeared to be a
bushtit nest. In the midst of a bowl of feathers
was an off white, centimeter sized egg. It was
pointed at one end, much more than the bushtit
eggs you see on-line. So, perhaps, this is an
egg that failed to hatch. The other possibility
is that this is the fortuitous remains of a
predated nest but it seems unlikely that such a
predator would have missed out on one last juicy
egg. Alan recoiled form the potential feather
mites but Viveca cradled the nest and egg all the
way to Avery garden before deciding that she
didn't really want it.
I think the highlight of the day is not a bird or
a time but a place. In the past, there have been
two or three hummingbird feeders scattered around
the yard of the house next to the entrance of
Tournament Park. The feeders were surprisingly
weak as a producer of hummer sightings but we
could often pick up one around the yard. This
time, there are three hummingbird feeders next to
the window and we see half a dozen hummingbirds
sitting around the bar getting drunk on sugar
water. Basically, once a hummingbird takes on a
big load of sugar water it takes him a while to
recover, so if your feeder is one of the
perchable varieties, he will end up just sitting
there for several minutes while he digests the
sugar.
Generally, if you put out one hummingbird feeder,
you will get one hummingbird because he/she will
defend this food source against other
hummingbirds. If you put out two hummingbird
feeders at opposite ends of the yard, you are
likely to get one or two hummingbirds because the
individual feeder can and will be defended. Put
out two or three or four or five close together
and you will get many hummingbirds, the critical
mass of feeders depending on just how feisty the
owner is. The resource has become so abundant and
so concentrated that your resident Anna's will
not be able to defend it. Once he/she gives up,
comity prevails, antagonism ceases, more or less,
and everybody who wants to can come and get a
drink. In this case, we saw several Anna's, a
striking adult male black-chinned hummingbird
with a sharp white scarf, and a juvenile
black-chinned. We already had a Selasphorus
acquired in the pre-walk phase, so we were up to
a three hummingbird day. The only thing that
could have brightened the event even more would
have been a Costa's hummingbird but no luck.
So you want to attract hummingbirds? You can do
it the natural way by planting hummingbird
friendly flowers like Garten meister fuccias or
penstemons (basically anything with elongate
flowers), which is what I do, or you can do it by
buying one or more hummingbird feeders. If you
are going to go the feeder route, it's very
important that you take the same attitude that
you would for a child bringing a cat or a dog
into the household. Somebody must be willing to
commit to proper maintenance of the feeder or you
will be killing hummingbirds. What does that
mean? Boiling sugar water (never use honey),
swapping it out every couple of days, cleaning
the feeder frequently (1/4 cup of bleach or
vinegar to a gallon of water, soak for an hour
and rinse thoroughly is the standard recipe,
although I would personally be inclined not to
use bleach if you have a plastic feeder because
of the potential for leaching the plastic, and
constant vigilance for the onset of mold (take
off line immediately). Ease of cleaning, which I
define as access to all surfaces, is very
important. If a bottle brush can't get at every
surface, you are asking for trouble. There are
many sites on-line that you can visit for advice
and your neighbors probably have an opinion, too.
Ask your local experts. Mostly, you will get
hummingbirds once they figure out that the feeder
is a food supply but the unexpected can also
happen. One day a couple of years ago, my
neighbor told me that he had been forced to take
down his feeder because a big black bird with a
yellow belly had been attacking it. I admitted to
being curious, so he put it back up and we soon
had a Williamson sapsucker bashing away at the
fake yellow flower ports! Somehow, this bird had
discovered that there was food to be had for the
taking, provided he was willing to batter the
port into submission and leakage.
I bring you in the end to our midden minds that
forget to feed the dog but leave the cat food out
at night for raccoons. They wash it down with
mallard eggs and take an aperitif of a dying
Anna's. He was full of moldy sugar water and
then he starved, not so happy coloring your day
for a little bribe. We have a killing winner.
Behind the promise of free beer and eternal
salvation, it is the aggregating power of a
highway right of way. Did you sell? Did you
buy? Did you acquiesce? Do you vote? Your
hummer will never know. He's dead and the serial
killers look to your windows and smile. Your cat
caught a sparrow in his dream.
The date: 7/23/2012
The week number: 30
The walk number: 1153
The weather: 82 F, sunny
The walkers: Alan Cummings, Kent Potter, John
Beckett, Viveca Sapin-Areeda, Vicky Brennan
The birds (17):
Rock Pigeon
Northern Mockingbird
House Sparrow
Mourning Dove
House Finch
Anna's Hummingbird
Acorn Woodpecker
American Crow
Mallard
Hummingbird, Selasphorus
Lesser Goldfinch
Red-masked Parakeet
Nuttall's Woodpecker
Black-chinned Hummingbird
Bewick's Wren
Bushtit
Black Phoebe
--- John Beckett
Respectfully submitted,
Alan Cummings
8/1/12
http://birdwalks.caltech.edu/index.html
7/16/12
It could have come from a disappointed sigh that
turned in one frame from something we had to
something we didn't have. One person could have
scanned the sky or a bush at just the right
moment to catch the signature of an avian motion.
It could have come from not making the mistake of
turning a new species into one on the list.
Somebody could have heard something. It could
have come from our two rock pigeons, stalwarts of
the last couple of weeks, not deciding to be just
a little different today, so that we missed them.
One more bird, one more dying quail, one more new
species and we would have tied the record for
week 29. As it is, we ended the walk with 15
species of birds, one shy of the record, three
above the median, and seven above the worst
score. I didn't calculate it but we undoubtedly
had a positive score on the Alanometer because we
were well above the median. It was a successful
walk.
See the plots at
http://birdwalks.caltech.edu/bird_data/species_time.html
and
http://birdwalks.caltech.edu/bird_data/two_plots.htm
Last week, Alan picked up an acorn woodpecker and
I had been hoping that we would get another one
this week. It was not to be. I grant you that
lunchtime is not the best for an acorn woodpecker
check, so I remain hopeful for next week, but the
early returns are not strongly suggestive of a
new family moving onto campus.
This week's curiosity and highlight has to lie in
the presence of numerous Bewick's wrens, at least
three that I remember, and I might not have seen
them all. It would be a serious stretch to
suggest that Bewick's wrens are a rare sighting
for us. After all, we saw them on 18 walks last
year, so we had a one in three chance or so of
seeing one on any particular week. Ubiquity is a
recent phenomenon, however. Last year was the
best Bewick's wren year in the history of the
walks (we had 14 sightings each in 2009 and 2010
and have had seven so far this year). Bewick's
wrens are another example of shifting avian
demographics in our neighborhood. We didn't see
any Bewick's wrens before 2002. We bounced
around between four and seven sightings per year
between 2003 and 2008 and then doubled up to 14 -
18 over the last three years (we now have seven,
so far this year). House wren sightings date
back to 1989 but they were rare (0 to three
sightings per year, averaging 0.7) until 2006,
when the numbers ballooned. So, we appear to
have had a significant range expansion of wrens
onto campus over the last decade and the two
species appear to be reasonably compatible
overall since numbers of sightings have been
increasing for both.
A house wren will not tolerate a Bewick's near an
operative nest but Bewick's wrens are like cats.
They are really good with boundaries once
established and you will often have multiple
house wren territories enclosed within a Bewick's
wren's territory. It also helps that Bewick's
wrens tend to breed earlier than house wrens and
often stick to one clutch, even in Southern
California. House wrens generally double brood.
All of the wrens manage to get along, although
this collegiality is apparently a western
phenomenon. In the midwest, house wren range
expansion tends to come at the expense of
Bewick's wrens, although a lot of this is due to
human induced changes in habitat. House wrens
like open grassy areas with nearby trees; the
Bewick's like a mixed regime of open areas with
nearby dense underbrush. Also, Bewick's can
handle aridity somewhat better than house wrens,
so there is a natural parsing of range,
especially in places like the Sierras that are
susceptible to periodic droughts, and I would
expect that the Bewick's will do just fine
relative to house wrens over the next few
centuries.
Our house wrens are most frequently seen in the
Maintenance yard and, during the breeding season,
in the north end of Tournament Park where there
are two excellent nesting holes. I don't believe
that we have ever seen a Bewick's wren nesting in
one of the tree holes in Tournament Park. They
are much more opportunistic about site selection
than house wrens. They are certainly willing to
use an old woodpecker hole if one is available
but any good crevice will do and, given the massive
demand for nesting holes among secondary hole
nesting species, it is usually a crevice of some
sort that they get. There are examples of them
using discarded tin cans. As any local Bewick's
could tell you, "If a house wren wants one of
those tree holes, I let him have it. It keeps
him quarantined in the south corner of my
territory and it's not like I need one for
myself. Besides, he'll be gone soon enough."
That last comment was telling. Bewick's wrens
are resident, although there is some down-slope
migration leading to some extra Caltech sightings
in the winter, and the house wrens tend to
migrate south out of our area after breeding,
although I was unable to find out just where they
go (presumably, someplace in Mexico but perhaps a
little further south). It's fairly common for
the local Bewick's wren to make use of or take
over an abandoned house wren's territory and I
suspect that this is at the root of the multiple
Bewick's sightings this week. In fact, one
reason I was pretty confident that our Tournament
Park house wrens had fledged is that we saw a
Bewick's wren on the fence in Tournament Park,
within the house wren's normal foraging area.
This would almost certainly have led to a verbal
and, perhaps, physical squabble last week when
there were definitely still house wrens in the
nesting hole.
Now, I don't want to give you the impression that
Bewick's wrens are completely cute, cuddly, and
laid back. They will destroy the eggs and
nestlings of other birds, a feature common to all
wrens, apparently. Also, if you want to tease a
little bigotry out of a Bewick's wren, just get
him talking about song sparrows. Song sparrows
and Bewick's wrens are directly competitive,
using similar foraging heights and have a liking
for similar insects (the parents eat seeds but
keep their young on a mostly insect diet). Also,
as our Bewick's interviewee would tell you, "A
song sparrow song is nothing but a disgusting
low-brow bastardized version of a proper Bewick's
wren song. Those guys shouldn't be allowed to be
heard in public and they definitely shouldn't be
allowed anywhere near my territory." He should
know. A male Bewick's wren will maintain his
territory throughout the year and he will sing
throughout the year. Most birds stop singing as
soon as the testosterone levels drop at the end
of the breeding season. Our Bewick's wrens take
their song singing very seriously, leading to
full year commitment to the art.
The week number: 29
The walk number: 1152
The weather: 73 F, sunny
The walkers: Alan Cummings, John Beckett, Melanie Channon, Viveca Sapin-Areeda
The birds (15):
House Sparrow
Mourning Dove
House Finch
Anna's Hummingbird
American Crow
Black Phoebe
Lesser Goldfinch
Red-masked Parakeet
Parrot, species
Bewick's Wren
Hummingbird, Selasphorus
Black-chinned Hummingbird
House Wren
Bushtit
Hawk, Species
--- John Beckett
Respectfully submitted,
Alan Cummings
7/30/12
http://birdwalks.caltech.edu/index.html
7/9/12
Our local pair of rock pigeons seem to be on a
timer that just happens to work for us. The
residue of their flight along California
Boulevard at noon is an early capture. We take
it but it is the most delicate of captures. If
they shift schedules by a few minutes in either
direction or change route by half a block or even
a building, we will miss them. Still, we are off
to a good start and in the end, we have a record
breaking day with 17 species. Seventeen may not
sound like much to those brought up on 30 bird
walks of the Spring but the previous record was
only 15. So we have a new record for week 28.
The king is dead! Long live the king (at least
until next year)!
See the plots at
http://birdwalks.caltech.edu/bird_data/species_time.html
and
http://birdwalks.caltech.edu/bird_data/two_plots.htm
As a bit of a non sequitor before launching a
description of this week's highlights, I would
like to revisit the Cooper's hawk of last week
rooting around a jacaranda. After some thought,
I now suspect that the hawk was looking for finch
(or other bird) nests. It doesn't take a lot of
energy to look around and there are obviously
finches in the immediate area, so it seems cost
effective to check things out. Cooper's hawks
generally specialize in taking small songbirds on
the fly but they are also significant nest
predators in some areas. Hopping around a tree
seems like a reasonable strategy for nest
locating if you don't have anything better to do,
especially if you have just eaten one of the
parents. Now, back to your regularly scheduled
programming.
Sometimes, with a record, you can point to
unexpected captures providing a boost to the
species totals but, almost always, it is an
unusually good day with those birds that you
would normally expect to encounter. This time we
had a bit of both. It tends to be feast or
famine with acorn woodpeckers. In principle, the
campus is capable of supporting multiple families
of acorn woodpeckers. We have a fair number of
oaks, some excellent anvils, and a reasonable
collection of their preferred prey, large insects
like bees, wasps, and beetles. Unfortunately, we
also have a liability happy program of pruning
away dead wood and destroying the granaries where
a family of acorn woodpeckers store their nuts.
Lose your granary or a major oak and you are
going to leave town. Last year, we had at least
one family in the campus area, leading to a
string of sightings but they left rather suddenly
and we have since been pretty much bereft of
acorn woodpeckers. Today, Alan picks up a
solitary individual near the end of the walk. Is
this a dispersing juvenile, the edge of a family
territory centered off campus, or the start of
something big?
The acorn woodpecker may be more important in the
sense that it represents a future potential (we
may capture this bird or family members in future
weeks) but the highlight bird has to be a
fortuitous and much rarer bird walk capture. We
come out of the Maintenance yard and see nothing
except a small brown bird sitting patiently on
the high backstop fence at the opposite end of
the playing field from where we were. Usually,
these sightings turn out to be house finches or
house sparrows but there is always the
possibility of something more exotic like a
nutmeg mannikin, which is not yet on the Caltech
bird list, although I have seen them in Pasadena
and Sierra Madre. So these far field sightings
are always worth the price of a side trip by
somebody in the group and I volunteer to go over
and check it out while the rest of the group
proceeds to Tournament Park. I approach, and from
what I can tell from behind, this is an odd bird.
There are arcs of spots or pins (not yet grown
out feathers) on the wings and, when it turns its
head slightly, I can see a large asymmetric,
decidedly non-finchy/sparrow/grosbeak bill with
some yellow about the face. I eventually come
around to where the bird is facing out and I see
a breast criss-crossed in brown bands on a
lighter background. The bands intersect,
creating a mosaic effect, so this is clearly not
a weird house finch. What is it? Hopefully, you
won't take this in an apologist motif but, to me,
the key to being a goodbirder is to know when you
don't know. If you can resist the temptation to
plug your bird into a not very suitable
appellation, you will be more likely to get the
assignment right in the end. So, I stare at this
bird from multiple angles, which of course means
that I have completely lost contact with the
group. I keep looking. The bird says nothing
that I can hear. I keep looking. Finally, I
decide that I have stored away as many field
markings as I am likely to get and leave. I meet
the rest of the group on the driveway between
Wilson Ave and Tournament Park and announce that
I don't know what the bird is, that I thought it
was a "juvenile something in the starling size
range", and that it was still there when I had
left. This announcement was met with a mixture
of disbelief and good natured derision. I am
both optically and aurally challenged but,
usually, if I can get a good look at a bird, I
can identify it. This time, I do not have a
field guide and I am only certain that I do not
know. I had failed the group and could only hope
that I would either figure out what it was from
the Sibley, or on-line later, or that the bird
would stick around long enough for somebody else
to brand the species.
So, the group ambles out onto Wilson Ave. and,
for once, I am forcing the pace (for me) but Kent
and Alan make it to the gym first. Almost
immediately, they glom onto a bird on the fence
and almost immediately conclude that this is a
house finch. I'm starting to get some smirky
looks. Fortunately, Alan then spies my bird and,
after a quick look, he heads for his Sibley
(thank God!). After trying on a suit of grosbeak
juvenile, we land on the correct answer, a
brown-headed cowbird juvenile. A later check on
line confirms the identification. We had our
first cowbird of the walk in over six years.
This bird was, presumably, dispersing after
fledging from the nest of some unknown host.
If you live near a horse stable or in an
agricultural area, you might not think much of a
cowbird but the flux through our area is modest,
which is a good thing for the locally breeding
birds because brown-headed cowbirds are obligate
brood parasites. The female lays her eggs in the
nests of other species (usually but not always
one to a nest) and the "foster parents" are stuck
with the task of hatching the egg and raising the
young to fledging. That's the ideal scenario
from the cowbird's perspective, anyway. This
type of parasitism is a unique behavior for a
North American bird. There are quite a few
birds, especially among shorebirds and gulls, who
will lay the odd egg in the nest of another
member of their own species but not many birds
lay eggs in the nests of other species.
So, how does this work? A day in the life of a
breeding season female cowbird begins before
dawn. She will have roosted with other cowbirds
near a concentrated food source where there are
insects to be stirred up and waste grain to be
scarfed up. In today's society, that usually
means a pasture, corral, or some other
agricultural endeavor. She awakes, perhaps does
a little preening, and then heads off on a
commute to her morning job that could be anywhere
from a couple of kilometers away to twenty. She
gets there, still before dawn and sets up
shop on her first observation post, a perch on a
tree with a good view of several bushes and
trees. She settles in and watches a pair of
Wilson's warblers bringing nest materials. They
come into the nest site from multiple angles and
via circuitous paths but she is patient and
figured out where the nest was a couple of days
ago. After they both leave to acquire some more
nesting material, she pops over to check out the
nest. Yes, it's almost finished (it's a several
day exercise). "The warbler will be laying eggs
tomorrow", she thinks. She goes back to her
perch and turns her attention to a pair of
warbling vireos. She laid an egg in their nest
yesterday and the female had accepted the egg
(this might not have gone as well for a cowbird
in the east where warbling vireos tend to reject cowbird
eggs by puncturing them and removing them from
the nest but we are talking here about west coast
birds that don't have a long history of cowbird
parasitism and haven't evolved defense
mechanisms; cowbirds didn't get to Pasadena until
the early 1900s and didn't make it up to the
Pacific northwest until the 1950s). She flies
off to another perch, where she can observe more
potential nesting activity. This is how her
morning goes. She has an elongate ten acre
breeding territory to cover. Fly and observe
carefully. Fly and observe, carefully. Try not
to provoke anybody until you have to. Today, our
female didn't happen to lay an egg but on most
days of the breeding season, she will and, when
she does, it is usually before dawn. A cowbird
can lay an egg in 30 seconds, so most of her
morning is taken up with observations on
potential hosting opportunities. It's quiet time.
Around lunchtime, our female will fly back to
join other cowbirds in a feeding area and engage
in foraging and courtship activities.
It's a full day's work for a female cowbird
during the breeding season and it is also
dangerous work. She has to pick the right nest
to lay an egg in and potentially take a lot of
abuse from larger birds that don't appreciate the
offering (one thrush attacked a cowbird laying on
her nest and gave her about thirty pecks and
bites by the time she managed to lay her egg; she
left, a bloody mess but alive). She lays an egg
on most days during the breeding season and as
many as 70 for the year (female cowbirds in their
first breeding season will only lay about thirty
eggs). This takes a lot out of you and leads to
highly skewed sex ratios in cowbird flocks (about
1.5 males per female for adults versus 1:1 for
first year birds).
Brown-headed cowbirds are generalist brood
parasites. If you are smaller than or not much
bigger than she is, you have an open nest, and
she thinks that you will accept her egg and can
raise a chick to fledging, she will try to give
you one, whether you are a grassland sparrow or a
red-winged blackbird, or a warbler, or a
flycatcher. Hole nesters are more or less immune
from cowbird parasitism. Even if she can get in
and lay an egg, she won't be able to get out.
Cowbird traps are based on a similar principle.
You leave a 1.5 inch gap between two boards. The
cowbird can drop through the gap to get at the
free millet, you conveniently scattered over the
floor but she won't be able to get back out.
Some potential open nesting hosts are not
suitable even if it looks like they might be and
cowbirds occasionally try. House finches fail
every time. Cedar waxwings fail every time.
Mourning doves fail every time. A cowbird chick
requires insects in its diet, so an obligate
frugivore like a cedar waxwing doesn't work
because the cowbird chick will starve to death on
a rich diet of berries. You are not, in general,
going to waste the egg. House finches will feed
the chick seeds and it will starve to death
because it needs insects to grow. Mourning dove
chicks eat mostly seeds and crop milk. They are
unsuitable hosts because of their diet and
because they do things backwards. In most birds,
the chick gets food by reaching to the sky with a
gaping mouth and manna from your parent drops in.
Mourning dove chicks have to reach down into the
throat of the adult and drink crop milk. They
are hard-wired to know that they have to do this.
The cowbird chick doesn't know this. He reaches
to the sky and starves.
Cowbirds have an atrocious reputation because
they eject host eggs, lay their own and sometimes
destroy entire clutches of eggs in the nest of
birds that had the audacity to reject the cowbird
egg, the idea behind this mafiosa approach being
to encourage renesting and to make it less energy
intensive for the potential hosts to accept a
cowbird egg than to reject your egg. The
downside of acceptance is loss of productivity.
If you are a small bird like a black-capped
vireo, it's a death sentence for all of your
chicks and the response tends to be nest
abandonment. Even if the foster parents
successfully fledge their own chicks, their
productivity will have dropped relative to
conspecifics that weren't parasitized. Just to
take one example, Bell's vireos in one study
averaged three fledging young in an unparisitized
nest, 2.4 if they deserted and built elsewhere,
and 1.5 if they accepted the cowbird. One pair
deserted six nests in succession as a cowbird
found them each time. On their seventh and last
nest of the season, they succeeded in hatching a
full clutch of vireos only to have the nest
predated. The cowbirds hatch faster than their
hosts, are bigger than their "siblings" and
require more provisioning. The host parents may
be able to keep up but this also has its costs.
They will have a reduced life expectancy because
of all the energy they have to put into the
cowbird chick at their own expense.
It's easy to blame cowbirds for the decline of
many bird species and people have, but this is, I
think, mostly bad press. Let's take the
Kirtland's warbler, which is the poster child for
a threatened species heavily parasitized by
cowbirds. If the problem was all about cowbirds,
you would think that getting rid of any cowbirds
in the breeding grounds would solve the problem.
So, we institute a very effective cowbird removal
program and knock the local parasitism rate from
93% to 3%. Kirtland warbler numbers stabilize
(i.e., the population is no longer in free fall)
but the numbers have not been increasing. What's
the problem? We got rid of the cowbirds. Well,
we don't just do proactive stuff like trapping
cowbirds. We also have the nasty habit of
destroying habitat and fragmenting forests
(cowbirds don't do well in deep forest but they
love a good road and so do most nest predators).
Kirtland's warblers have very specific nesting
requirements (Jack pine forests found in a few
counties of Michigan and bits of Wisconsin and
Ontario) and very restricted, wintering grounds
on a few Caribbean islands that are highly
vulnerable to development. It's a bad
combination and killing off a bunch of cowbirds
is only buying us a little extra time to peer
into our own souls. We have a somewhat similar
problem with Wilson's warblers breeding along
coastal California. They are in serious decline
and stresses do include cowbird parasitism but
there are also corvids, cats, and raccoons, all
of whom are taking advantage of the fine dining
facilities and foraging opportunities that we
provide; they are eating the odd Wilson's warbler
and their eggs or nestlings on the side and the
numbers add up to an unsustainable warbler
population. They are looking into the eyes of
local extirpation.
Finally, I just have to mention screaming
cowbirds. Not every cowbird is a brood parasite
but screaming cowbirds are. They are South
Americans who work with just one species, the
bay-winged cowbird who, incidentally, is not a
brood parasite. Brown-headed cowbirds are
generalists and their eggs and young often don't
look much like those of their hosts. Adult
screaming cowbirds and bay-winged cowbirds have
totally different appearances but the eggs and
nestlings are virtually identical. Charles
Darwin would have loved them.
The date: 7/9/2012
The week number: 28
The walk number: 1151
The weather: 89F, sunny
The walkers: Alan Cummings, John Beckett, Viveca
Sapin-Areeda, Vicky Brennan, Kent Potter
The birds (17):
Rock Pigeon
Northern Mockingbird
Mourning Dove
House Finch
Anna's Hummingbird
Acorn Woodpecker
American Crow
European Starling
Lesser Goldfinch
Spotted Towhee
House Wren
Bushtit
Hummingbird, Selasphorus
Brown-headed Cowbird
Swallow, species
Black-chinned Hummingbird
Black Phoebe
--- John Beckett
Respectfully submitted,
Alan Cummings
7/27/12
http://birdwalks.caltech.edu/index.html
7/2/12
We acquired no new record this week. We did
reasonably well with 16 species but there seems
to be an infinite gulf between what we saw and
the existing record of 18. Do not construe this
as a complaint, however. It was a walk of
considerable interest.
See the plots at
http://birdwalks.caltech.edu/bird_data/species_time.html
and
http://birdwalks.caltech.edu/bird_data/two_plots.htm
We had a nice view of a house wren foraging near
the entrance of Tournament Park. He flies over
to one of the slides and roots around for a while
and then flies back over to his nest hole,
carrying what appears to be a ground beetle.
Bedlam! Viveca and Vicky were almost directly
underneath the nest and report a full concert but
I don't think the beetle was too happy about it.
A few seconds later, the wren pops out with a
fecal sac. Holes may provide a relatively
protected environment for bringing up birds but
there's no indoor plumbing. Some birds actually
eat the early fecal sacs because the chicks'
digestive systems are inefficient and there is
still significant energy to be pulled out
provided your palette isn't too discriminating.
As the chicks get a little older, there is not
much you can do except to cart it off to the
local landfill.
Another highlight came towards the end of the
walk. We see two black beaks protruding up from
the black-chinned hummingbird nest. We didn't
see a feeding but this probably means that they
are within ten days or so of fledging.
Although these were interesting vignettes, I
would propose the highlight of the walk to have
been in the walk before the walk. Viveca, Vicky,
and I all congregate near a jacaranda outside
Millikan. We can hear multiple house finches
flinging out whistled whets but the center of
attention for us and, I am sure, the finches, is
a large (hence likely female) adult Cooper's
hawk. She hops from branch to branch, stooping
to peer under branches and lifting her head to
peer over them. If she had been a lot smaller, I
would have said that she was foraging for insects
or lizards. I could only classify the activity
as strange without coming to any resolution over
why she was engaging in such an odd behavior
because we had to leave to make the entry point
of the walk. Enlightenment would have to wait
and, I must admit, probably never come. We
didn't see the hawk again but, as we stride up
the path around Throop ponds to end the walk,
Alan, who seems to know about 10% of the people
on campus by name, is accosted by an acquaintance
coming down the path. She is simultaneously
excited and repulsed as she describes having seen
a hawk by Millikan catch and eviscerate a
"sparrow" (almost certainly a house finch).
Nature was in action and this seems to be at the
root of our Cooper's capture at the beginning of
the walk. Either our hawk had just eaten a finch
and was looking around for more or she was hoping
for lunch and hadn't caught one yet. Given all
the finch chatter surrounding her, I'm inclined
to think that a kill had already happened.
So, in the end it comes to this. You are a
songbird and everybody loves you. The local
hawks love you. The local cats love you. The
local ravens and crows love you. Even the local
snakes love you. With all this love surrounding
your world, it is really important to signal
fitness and genetic quality to prospective mates
so that at least one conspecific songbird can
also love you. How can you do this with no
ascending acquisition of killing love? How can
you disappoint your fan club? You could just
advertise with an in your face red like a tanager
and take your mortality lumps or you can go for a
willful subterfuge. It's all a matter of
perception. Let's take mammals, high on the
enemies list. We can see red reasonably well but
humans tell color using just three cones or
channels, one most sensitive in the yellow/red
part of the visible light spectrum, another in
the greens and a third in the blue/violet. So, if
you want to fool a human with a glaring color
scheme, you probably don't want to do it in the
middle of the visible light spectrum. Humans
are, however, blind in the UV, wavelengths of
light below about 400 nanometers, because our
eyes absorb UV light (what goes in, never gets to
the bottom where it can be processed). Cats
don't do any better. They have excellent night
vision and are terrific motion detectors but
don't ask one to work out a UV signal. If she
doesn't merely ignore the request, she will
rather stiffly inform you that this sort of light
doesn't exist. It's a boring topic. What about
raptors? Hawks and corvids like ravens and crows
have four cones to our three and one of these is
optimized for violets. They are not, like us,
entirely blind in the UV and kestrels are known
to pick up on some UV signals but all of these
birds have very poor vision in the UV. Snakes?
They don't tend to use color as a hunting guide
unless you want to count thermal imaging and
using heat signatures for courtship would take an
awful lot of energy. Something more energy
neutral is needed. So, we must have an answer to
a possible courtship mechanism for a songbird
that minimizes risk of consumption with the
songbird as the consumee and it's not in the
infrared. If you are a songbird, a good way to
go is to be flamboyant in the UV and use the
visible light spectrum for camouflage. So, most
songbirds optimize one of their cones in the UV.
A good example of how this comes into play is
provided by budges. They have fluorescent
pigments in the crown and cheek feathers and
these are used to signal fitness. Put some sun
block on the head and you turn Casanova into a
complete dud. Not convinced. Want something
less colorful in the visible light spectrum?
Consider bushtits. Can you tell me how to tell
the difference between an adult male and female?
"Sure", you say. The male has dark brown eyes
and the female has yellow eyes with a dark iris.
Ok. That can work if you are a meter or two away
and the bird isn't moving around too much. What
do you do if you can't make out the eye color?
Ah, silence. If only you could see in the UV,
you wouldn't have this problem. Bushtits are
extravagantly flamboyantly beautifully dichromic
in the UV and if you could see them in the UV you
would have about as much trouble telling sexes
apart as you would a perched pair of western
tanagers in breeding plumage. So, the next time
you look at a drab, drab, drab bird consider the
possibility that you are actually blind, blind,
blind, blind. It's all a matter of perception.
Bushtits have it and we don't and that's just the
way the bushtits like it.
The date: 7/2/2012
The week number: 27
The walk number: 1150
The weather: 78°F, sunny
The walkers: Alan Cummings, Viveca Sapin-Areeda, Vicky Brennan, John Beckett
The birds (16):
Northern Mockingbird
House Finch
Anna's Hummingbird
American Crow
Cooper's Hawk
Black Phoebe
White-throated Swift
Lesser Goldfinch
House Wren
Bewick's Wren
Band-tailed Pigeon
Bushtit
Common Raven
Northern Rough-winged Swallow
Hummingbird, Selasphorus
Black-chinned Hummingbird
--- John Beckett
Respectfully submitted,
Alan Cummings
7/13/12
http://birdwalks.caltech.edu/index.html