Vocalizations are an
important, and sometimes critical, aspect of identifying flycatchers of the
genus Empidonax. Alder and Willow Flycatchers, for instance,
are so similar morphologically that many individuals cannot even be separated
in the hand, but their vocalizations are diagnostic. Mostly it is the song that birders learn,
but oftentimes the call notes are equally important to learn - and in the case
of Dusky vs. Hammond's Flycatchers, the call notes are more easily distinguished
than the songs.
But Empidonax flycatchers have more
vocalizations than are typically described in a field guide, and the line
between what is a "song" and what are "calls" is unclear in
this genus. In most Empidonax species, and in fact many other flycatchers (e.g. pewees
and phoebes), the male sings a "dawn song", given only at first light,
that is a longer and more complicated version of its daytime
vocalizations. Sometimes a vocalization
that is referred to as a song (e.g. the "FITZ-bew" of the Willow
Flycatcher) may actually be analogous to another species' "position
note" (e.g. the two-note call of the Cordilleran Flycatcher): in both
cases, these are calls uttered throughout the day, typically by males. However, males and females are identical in
all Empidonax flycatchers, so exceptions to these rules go unnoticed unless
one is studying a group of color-banded birds, whose sexes have been determined
in-hand. Below, I will use my experience
with a color-banded breeding population of Cordilleran Flycatchers in Colorado to
describe each vocalization, its context, and which sex uses it and when.
1. Dawn Song or Primary Song
Play Recording
The Cordilleran
Flycatcher has a three-part song, used only by the male during the breeding
season. Early in the season this may be
sung during the daytime, presumably by males that have not yet attracted a
mate. Later in the season, mated males
sing it only for a few minutes at dawn.
2. "Male Position Note"
Play Recording
This is the common call
heard throughout the day in summer, and during migration and winter, is the
only way to distinguish the Cordilleran Flycatcher from its closely-related
look-alike Pacific Slope Flycatcher. In
the literature, this two-note call is referred to as the "male position
note". I use quotes here, because
although I have found that the male uses this call consistently, I have also
observed females using it. Sometimes the
female utters a higher-pitched, slurred version; other times it is identical to
the male's call. The most frequent
context seems to be territorial advertisement - saying "I'm here and this
is my territory". The male utters
this call non-stop throughout the day early in the season, when territorial
boundaries are being established. He
then goes quiet much of the time while the female is incubating and while he
and his female are feeding nestlings.
Later in the season though, I've noticed that the male resumes his
near-constant use of this call throughout the day; this coincides with two things:
1) fledging, which leads to a breakdown in established territories as the
fledglings wander around; and 2) arrival of early migrant Cordilleran
Flycatchers, most likely failed breeders from nearby who, with no time left for
a second nesting attempt, have abandoned their territories and begun
pre-migratory wandering. These forces
put pressure on the pair to defend their territory, and it is during this time
that I have seen the most frequent use of the "male position note" by
females.
Nothing yet is known
about the Cordilleran Flycatcher's behavior on the wintering grounds, but stay
tuned - I have received some funding to work on this species in Mexico, and I
bet you anything that both males and females defend winter territories using
this call. We'll see!
3. "Female Position Note"
Play Recording
Again with the quotes,
because while the female uses this vocalization far more frequently, I've seen
males use it on occasion. This is a
single, high-pitched call, and although I suspect it is used in multiple
contexts including communication with the male, most often it seems to be given
in alarm. Anytime I approach a nest or
fledglings, the female gives this call repeatedly, accompanied by nervous
tail-flicking. Her fledglings know what
it means, too - they go quiet and still when they hear this call.
After two seasons of
close observation, I've noticed slight variations in this call, even within
individual females - sometimes the note is flatter, sometimes sharper, and I
strongly suspect this variation is related to context. I'd love to get some high-quality recording
equipment and study this.
4. "Gurgle Call" or "Interaction Calls"
Play Recording
This is a call I've
never seen mentioned in any field guides.
It's a soft series of rolling or gurgling notes, used by Cordilleran
Flycatchers when in close proximity to each other. Pairs use it when approaching each other,
such as passing one another while feeding nestlings, and strangers use it while
chasing each other. Thus is it often
used in aggressive contexts (both among strangers/neighbors and within the
pair), but might also have a non-aggressive context within the pair. It is used by both males and females.
5. "Soft Interaction Calls"
Play Recording
This is another type of vocalization used in close interaction between individuals. It is soft, lower-pitched than the position
notes but not as low and growling as the aggressive "gurgle
call". Both males and females use
this, and the most frequent context I've noted is around fledglings, especially
when the parents are trying to gather up a scattered brood.
It's a joy to be able
to study a species intensively, to learn the context of its various
vocalizations and to come to know calls that are not described in most field
guides. I want to acknowledge Xeno-Canto (www.xeno-canto.org) as the source of the vocalizations used in this post - this is a fantastic repository for bird vocalizations. Someday I hope to purchase some nice recording equipment and contribute my own recordings to this site.
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