Spring has been summoned and I am a bit behind. That is what a broken timing belt and efforts to buy a new car will do, but that is a tale for another time. A few of the American Goldfinch and Lesser Goldfinch remain. Back in February when I was inspired to record the Lesser Goldfinches song they had just begun to sing. I had only recently learned that they mimic other bird’s songs. A couple of years ago I had learned about Cassin’s Finches and their delightful mimicking and last fall tuned into the profoundly talented European Starling. I have since learned that many many more birds than I realized add the sounds of other birds, and some mammals and machines, into their repertoire.
Lesser Goldfinches, like many birds who mimic, have a long song with much variation. February in California can afford some lovely days outside on the patio listening to birds. I began to notice that some of the Lesser Goldfinch had switched from calling to singing above me in the oaks, and the closer I listened I clearly heard Kestrel and Robin calls. Cool! I utilized this opportunity to play with my new toy, an iPod Touch. I had already recorded some spectrograms of bird sounds with it. Why not record the song directly and use it to learn how Raven Lite works? Below is a sample I captured. It is rough and there are songs and calls of other birds present, but WOW household technology has come a long way from tape decks and voice recorders.
The more I listen the more I hear other songs and calls mimicked. What do you hear? Recently, I co-lead a local Audubon trip and someone asked, “what is that?” I had to tune in to the varied, melodious song for just a couple of seconds before I knew it was a Lesser Goldfinch signing above. We listened and I explained what I had been learning, that they had a varied song which included mimicry, when suddenly I heard a Canyon Wren song included in its repertoire. More Cool!
In attempting to research why they mimic, I learned a few things. For one, there is not much out there, at least in the realms that I am aware of currently, on why birds mimic. The best reference I could find on this query was The Straight Dope and David Sibley. I guess you could say that I have been living under a rock because I had never heard of The Straight Dope, but apparently it is the disseminator of facts about all things. It states:
“But many birds mimic the calls of other species, and have been known to imitate such things as telephones, alarms, and chainsaws. Why? The best guess is that imitation is the easiest way to increase the repertoire of calls a given individual can make. And what’s so good about having a big repertoire? There are several possible benefits: (1) A big repertoire can indicate to a female that a male has been around awhile and thus is a good survivor, with enough experience to be a suitable mate. (2) The response of a female or rival to a particular song is likely to decline after long repetition. Constantly changing songs may help to maintain interest in the listener. In fact, it is often species that sing continuously for long periods like the mockingbird that have the largest repertoires. (3) Changing songs could interfere with a rival’s–or perhaps a predator’s–ability to track the singer’s wherabouts.”
Sibley writes in his Guide to Bird Life & Behavior, “…mimicry may be a way individual males can quickly add new sounds to their repertoire…if the variety of sounds…is an important part of the signal.” He goes on to suggest, “Perhaps for mimicking species, males with large repertoires are advertising themselves as fast learners, rather than as individuals with some other trait such as old age,” adding to what The Straight Dope included as possible reasons why birds mimic.
I found a post by Sibley where he was responding to an inquiry into whether or not Lesser Goldfinch include certain songs and calls of other birds at particular times of the year. He wrote,
“That leads me to suspect that the imitating birds are responding to the season and not to the presence of the species being imitated. In other words, maybe the goldfinches learn a “spring song” and incorporate sounds they hear during spring, so the next year when spring comes their spring song just happens to include those imitations.
Mockingbirds are known to sing different spring and fall songs, with different amounts of mimicry and different phrases in each one. There could conceivably be more subtle shifts, adding or dropping phrases from their repertoire by weeks or months during each season.”
I find all of this fascinating.
Other tid bits I learned reading The Birds of North America Online, Kaufman Field Guide to Advanced Birding: Understanding what You See and Hear, Sibley Guides online blog, and Earbirding.com are that mimicked phrases were rarely repeated unless the song was long, some birds were mimicked even though they are not present in the goldfinches breeding habitat, some mimics learn new vocalizations throughout their lives continually adding to their repertoire, unlike most song birds which have critical learning periods during early stages of their lives, and interestingly close relatives do not seem to be mimics as in House Finches do not mimic yet Cassin’s Finches do, Lesser Goldfinches mimic and American Goldfinches do not.
Although, as Nathan Pipelow over at Earbirding.com suggests, perhaps we just do not know enough. He questioned whether or not we really know enough about the mimicking habits of House Finches and American Goldfinches back in his June, 2009 post and not a month later Sibley posted on mimicry observations in American Goldfinches among other species. It seems that the more we keep looking the more birds we find that do some form of mimicry.