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Archive for June, 2009

Female vocalizations in birds

by ocarmi on Jun. 27th, 2009 No Comments

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I received another comment to which I’d like to reply publicly:

Gay Bishop on Jun. 5th, 2009 at 10:52 AM
I am interested in information regarding female vocalizations in birds. I’m finding there is little information available on the subject. Is there a list of which native females do sing? thanks for your help. Gay Bishop”

This comment brings up a few very important issues, and I must admit that I’ve been quite neglectful. I’ve just returned from a week-long workshop on recording of natural sounds—birds in particular—and one message we received is that, while most people who record bird sounds like to focus on the most palatable ones—namely male song—there is a real need to document other vocalizations, among them call notes uttered under various circumstances, the vocalizations of young, and, of course, the vocalizations of females.

I’ve neglected female vocalizations, and, indeed, even female images, partly because I’ve aimed to keep my blog as simple as possible, and as accessible as possible, and the fact of the matter is that, often, the most easily visible and audible birds are males.

But there is no longer an excuse! I will therefore do my best to address the issues that I perceive in Gay Bishop’s comment.

First, female-specific vocalizations. In some birds, there are vocalizations that are specific to males, and others that are specific to females. This is true for several local species in the blackbird family (Icteridae). For example, when a male Brown-headed Cowbird (Molothrus ater) sings to a female, she often answers with a trill, or “chatter” call. An example of a male song can be found here. Males have several types of song—this is only one. Some more examples of song, as well as an example of the female chatter call, are posted here.
Male and female Brown-headed Cowbirds

Male and female Brown-headed cowbirds.
The female is on the right.
Photo credit: Tom Talbott, Seattle, WA

Male and female Red-winged Blackbirds
Male and female Red-winged Blackbirds.
The female is below the male
Photo credit: Jeff McCrory, Tacoma, WA
Male and female Red-winged Blackbirds (Agelaius pheoniceus, also in the blackbird family) form separate flocks in the winter, and I’ve noticed that their flight vocalizations are distinctly different. Unfortunately, I cannot find a recording of flying flocks of blackbirds. However, I did come across this page from a blog by Paul Driver, with examples of other Red-winged Blackbird calls unique to males and females. Paul Driver’s blog is incredible for documenting so many different kinds of vocalizations of so many species. The blog focuses on birds from the eastern United States, but many of the species occur here in the Bay Area as well.
Red-winged Blackbirds are common breeders in marshy areas. Flying flocks can be encountered in the winter in various places, such as Coyote Hills Regional Park in Fremont, where you might be able to see the birds close enough to tell whether they are male or female. A more impressive sight is the seemingly endless stream of giant flocks of blackbirds one sees in the winter in the Sacramento Valley.
Flock of blackbirds
Flock of blackbirds.
Photo credit: Mike Baird, Morro Bay, CA

Another bird with male and female specific calls is the Dark-eyed Junco (Junco hyemalis). This bird is very common in the Bay Area, and is often easy to find even during nesting. When you (unknowingly) approach a nest, the male may begin sounding deep “tup” calls. (A couple of examples of this call can be found on this page. Scroll down to the track labeled “Alarm call and other call notes.”) If you approach even closer, the female will appear and begin sounding sharper “tick” calls. (Unfortunately, I have not been able to locate a recording of this call.) The Dark-eyed Juncos’ local breeding season is quite long, beginning early in the spring and lasting well into summer, so you may still have a chance to observe these vocalizations firsthand. If you notice a male Junco tupping, approach it and see what happens.
Female Dark-eyed Junco
Female Dark-eyed Junco.
Photo credit: Jamie Chavez, California
Male Dark-eyed Junco
Male Dark-eyed Junco.
Photo credit: Nathan Hamm, Roseburg, OR
[But, please, don't harass the birds too long! You may expose the nest to predators. In some species, you may cause the parents to abandon the nest. With juncos, don't expect to find the nest! It is extremely well hidden in vegetation on the ground, and you are more likely to step on it than find it, or you may flush nestlings too young to survive out of the nest.]

Bishop asked specifically about female song. In some species, females do indeed sing. In Black-headed Grosbeaks (Pheucticus melanocephalus), females sing a song similar to, but not quite exactly like, that of the males. They can however sing the male version of the song. I learned from Dr. Alan Kaplan, former naturalist at Tilden Regional Park in the East Bay, that females will sometimes take advantage of this ability when sharing incubation duty with males. If a male has been out foraging a bit too long for the female’s taste, she will sing a male song. He, interpreting her song as that of an intruding male, will rush to the nest, at which point she will relinquish her post to leave him to incubate the eggs for a while.
Female Black-headed Grosbeak
Female Black-headed Grosbeak.
Photo credit: Maggie Smith, San Luis Obispo County, CA
While I have never knowingly heard female Black-headed Grosbeak song, as opposed to male, here is an example of the song of this species. Black-headed Grosbeaks are native to the Bay Area. However, I recorded this particular bird during my sound-recording class in the Sierra Nevada. I never saw this individual, and do not know whether it was male or female.
Male Black-headed Grosbeak
Male Black-headed Grosbeak.
Photo credit: Steve Ryan, Groveland, CA

Wrentit with morsel in its bill.
Female and male wrentits look alike.
Photo credit: Larry Tunstall, Brookrails, CA
Another species where both males and females sing is the Wrentit (Chamaea fasciata), a unique denizen of thick chaparral restricted to coastal California, Oregon, and Baja California, and the western Sierra Nevada foothills. In Wrentits, both male and female song consists of an accelerating series of “yips,” reminiscent of the pattern of sound of a ball bouncing on a table. The male version of the song (a recording of which can be found here) accelerates to a trill, whereas the female version does not speed up as much. (An example of a song that does not speed up quite enough to end in a trill can be found on this page—I don’t know whether it accelerates little enough to qualify as female song.)

Finally, Bishop asked whether there is a resource that lists which native species’ females sing. I did not find such a resource! As may be evidenced by my blog entry, even recordings of female vocalizations are (surprisingly) difficult to find!

Some simple google searches, however, for ‘female vocalization in birds’ or ‘female bird song’ and similar terms, retrieved some very interesting information, and I managed to track down quite a few studies on the subject. I discuss just a handful of them briefly below.

First of all, it should be noted that female birds can often be induced to sing male song via implantation of testosterone, and this practice has been used by researchers to study the acquisition of song.

Naturally occurring female song is another story.

Perhaps the most provocative study I came across was a collaboration between researchers in Belgium and France (L. Z. Garamszegi et al., 2006, published in the journal Behavioral Ecology), who searched the literature for mention of female song in European songbirds, and used statistical and phylogenetic methods to ask whether the ability of females to sing is ancestral—in other words, whether it is the rule rather than the exception. Despite a dearth of available data, they still managed to show that female song is the norm in two families, and they suggested that, with more information, it may turn out to be the norm for all European songbirds.

Many families of songbirds are common to Europe and North America, and so, what is found to be true of European songbirds is likely to be true of our songbirds as well.

In fact, female song may be ancestral to all songbirds. Songbirds are thought to have originated in Australia, and female song, apparently, has been commonly noted in Australian songbirds!

Garamszegi and his colleagues mention several possible explanations for the existence of female song, and these are identical to explanations that have been pursued for male song: attraction of mates, fending off of competitors—two hypotheses that I have mentioned in a previous column—and several that I haven’t, including coordination of breeding activities, and maintenance of contact with mates.

A study by researchers from the University of Cambridge (N. E. Langmor and N. B. Davies, 1997, published in the journal Animal Behavior) has provided direct evidence that female song may evolve for the purpose of competing for mates. The study focused on Dunnocks (Prunella modularis, a European bird). The researchers experimentally removed males from the study area to increase competition for mates between females. Females use a “trill” call to induce their mate to approach them. When two females were in direct competition for a single male, they increased their trill rates. Also, some of the females who shared males produced complex “songs,” which summoned their mates, but females who had a male all to themselves did not produce these songs!

For me, this study raises an interesting question: What is female song? If we remain male-biased, we may fail to recognize a female vocalization as “song” if it does not match a male “song.”

And this, of course, harks back to the question of what “song” is, and how it is distinguished from a “call,” which, as I have also discussed before, is quite a murky question. “Song” seems to imply a complex, or a palatable vocalization. However, for the purpose of a rigorous definition of “song,” the function of the vocalization has often been invoked. If a female utters a relatively simple and (to us) unpalatable vocalization in order to attract a mate, is it song?

As you probably see, bird song in general is a complex issue, and female song not well enough studied. I have provided a few examples of female-specific vocalizations, a few of female-song, and a few of research on female song. However, I have failed to find any central resource on female song. If you come across such a resource, please leave a comment, and let us all know!

Vocalizing female Red-winged Blackbird
Vocalizing female Red-winged Blackbird.
Photo credit: Julie Falk, Southern Michigan