Trilling 22 Birds with One Tone: The Northern Mockingbird

It was 10 in the morning and I was walking down Westheimer as the hustle and bustle of the city began to bloom. Noted journalist John Nova Lomax once referenced Houston’s infamous Westheimer road saying, “more than any other thoroughfare, [Westheimer] embodies Houston’s car-enamored, zoning-free ethos, a damn-near 20-mile phantasmagoria of strip malls, storage facilities, restaurants, big-box retail, office parks, apartment complexes, strip clubs, malls, supermarkets and the occasional church.” That’s probably the best way anybody will ever describe it.  So you can imagine why I was surprised to hear, above the car honks, bulldozers, café chatter, and shouting workers, a birdsong. Actually it was not only one, but many birdsongs. I thought to myself, I didn’t know Westheimer was a mecca for birds. Well, it turns out it was one bird…a mockingbird. He perched at the very top of a tree and sang his heart out to the world. And I assure you, the whole world could hear.

Northern mockingbirds (Mimus polyglottos) stand true to their name: they mimic the songs of other birds or even mechanical sounds and they are very good at it. When I first heard this guy singing on Westheimer I thought he was a Carolina wren. At that moment I was proud of my newly acquired skill of detecting birds by their songs (something I learned through the great Field Bird Biology lab I am taking this semester). Seconds later though the song switched and I knew something fishy was going on. Mockingbirds can only memorize bits of sounds, which they repeat several times before moving on to a new sound. Consequently, they are great at mimicking birds whose songs are repetitive, but birds with longer tunes like the Song Sparrow pose somewhat of a problem.

I was curious. As I sat and listened to the performance that day I began to count the different songs I heard. I got up to 22 and then gave up counting – I didn’t want to be there all day! I later discovered that however limited they may be in mimicking a lengthy tune, a male mockingbird’s repertoire can contain more than 150 songs! This is no small feat! (Listen to the mockingbird’s song here!) They build up their repertoires every season. Burnett found that spring and fall song repertoires have only 1% of their song types in common and that a minimum of 35%-63% of song types in a given spring repertoire occur again the subsequent spring; the rest are new. In addition, Kim Derrickson studied 4 male northern mockingbirds, analyzing over 10,000 song bouts, which are repetitions of a particular song type, over the course of two years. Between 102 and 412 distinct song types were identified for each male in a given year. Many of these song types (25.8-57.4%) occurred only once in this sample of singing behavior. Talk about fast learners!

I was expecting the physical appearance of the bird to match its colorful and varied singing repertoire. I was a little disappointed to find that this opera was coming from a gray-brown bird with a paler breast and belly and two white wingbars on each wing. Being about the size of a robin but a little slimmer, its size was not too impressive either. If I was a female I would say, “Why should I date you?” Because they have amazing vocal skills, that’s why. Charles Darwin once said, “The sexes of many animals incessantly call for each other during the breeding season; and in not a few cases, the male endeavors thus to charm or excite the female. This, indeed, seems to have been the primeval use and means of development of the voice, as I have attempted to show in my ‘Descent of Man.’ Thus the use of vocals will have become associated with the anticipation of the strongest pleasure which animals are capable of feeling.” Merritt supported Darwin’s observation in a study in which he studied populations of mated and unmated northern mockingbirds on the main campus of the University of Miami. He collected data during 2040 2-minute sample periods in which he listened for singing. He found that mated males sang continuously 13.9% of the time while unmated males sang continuously 41.8% of the time. Furthermore, the amount of singing by the male that lost his mate increased from 4.2% to 65% and that of the male that attracted a mate decreased from 45.8% to 6.7%.

Derrickson, besides looking at the frequency of singing like Merritt, also studied the variation in song at different periods of the mockingbird “relationship”. His data show that the frequency of occurrence of singlets, song types occurring only once in a sample, is 305 during ‘courtship’ as opposed to a much lower ‘prefemale’ (104) and ‘nest building’ (85). So this just goes to show how much more diverse the song types are when males are trying to woo females. Those males really up their game to impress the ladies! Some even continue to sing late into the evening. I have to admit all this is really beautiful on a pleasant summer day but for those of you who have had mockingbirds claim your backyards as their territory, good luck trying to get some shut-eye if that’s going on outside your bedroom at 11 pm!

Back on Westheimer, I couldn’t help but giggle at the mockingbird on the leafless tree in front of me. He kept hopping excitedly from branch to branch, all the while not ceasing his song. He sure liked to show off! When he opened his wings to fly the short distance between one tree and another, I could see beautiful white patches on them that were not visible when they were folded. I was able to get very close to him, maybe 5 feet – and the best part is he wasn’t even fazed! What a brave little guy. As I inched a little closer he cocked his head and looked at me while whistling out the lilting tune of a warbler. By the way he looked at me, I felt like I was meeting a bird that would never forget my face. In a way I was right! Douglas Levey did an interesting study about mockingbird recognition. His team asked a volunteer to stand near a nest for 30 seconds and touch it for half of that time on four consecutive days while the mother mockingbird was present. On the fifth day he sent a completely different person to do the same thing. The mother flushed (flew to the nearby bush to shout out alarm calls) from the nest at progressively greater distances when approached by the same intruder on consecutive days. Flush distance was significantly greater on days 3 and 4 than on day 1, increasing on average 320% over 4 days. By day four, mom was out of her nest when the volunteer was almost 15 meters away!  Flush distance for the control intruder on day 5 did not differ from flush distance for the first intruder on day 1. It’s amazing what these bird brains can do!

I revisited that spot on Westheimer two days later. Surprise, surprise – there was my little friend! I listened to his performance for a bit and then started whistling a repetitive measure. He stopped singing and listened to me. After a few bouts of my own I stopped and he started again. This time though, he incorporated my sound in his song! And so our conversation continued. You know, mockingbirds aren’t always a birder’s favorite – they chase off other birds, sing at the top of their lungs all day (and all night sometimes), and are not exactly exciting to look at. But I have to admit that the mockingbird is one of my all time favorites. You know why? He’s got personality.

REFERENCES

Burnett, L. J. 1978. Mockingbird song (Mimus polyglottos): An investigation within and across seasons. M.S. thesis, Univ. North Carolina, Greensboro, NC.

– Looks at variation of song in northern mockingbirds within and across the Spring and Fall seasons

Derrickson, K. C. 1987. Yearly and situational changes in the estimate of repertoire size in Northern Mockingbirds (Mimus polyglottos). Auk 104: 198- 207.

– Studied the singing behavior of 4 male Northern mockingbirds and analyzed them spectrographically to estimate repertoire size during different social situations

Derrickson, K. C. 1988. Variation in repertoire presentation in Northern Mockingbirds. Condor 90: 592-606.

– Studies the presentation of northern mockingbirds’ extensive repertoire in various reproductive stages using five measures (three versatility measures, bout length, and recurrence interval)

Levey, D.J. et al. 2009. Urban mockingbirds quickly learn to identify individual humans. Proceedings of the National Academy of Sciences.

– Explores the ability of Northern mockingbirds to adapt well to urban settings and how well they are able to recognize individual humans as threats and react accordingly

Merritt, P. G. 1985. Song function and the evolution of song repertoires in the northern mockingbird, mimus polyglottos. Doctoral dissertation. University of Miami, Coral Gables, FL.

– Examines the functional significance of song in the northern mockingbird and how it evol

Most consider the mockingbird to be plain but in my opinion they are beautiful in a simple way. Besides, why would you need colorful feathers when you are a professional singer?!

Oh, and what a wonderfully long, loud and varied song! The mockingbird is an excellent mimic. He can copy the melodious tune of a warbler, the clucking of a robin or the cawing of a crow. Mix in the sweet cadence of a veery and you have a performance that has no match!

A Northern mockingbird in flight - although they are decked in mostly gray plumage, the mockingbird is anything but dull. When you see him in flight, the first thing you’ll notice are his flashy white wing patches contrasted against his dark feathers.

Mockingbirds are quite territorial and aren’t afraid to chase or dive at animals that they don’t want on their kingdom. They will bother blue jays, hawks, eagles, and even your cat or dog!

Mockingbirds love to show off, making their presence known by perching boldly at the top of large shrubs and small trees.

Year-round range of the Northern mockingbird (The Birds of North America Online)

FIG. 1 from Derrickson 1987 - Spectrograms of early spring song by a male Northern Mockingbird. Fifty-six songs are organized into 11 bouts of different song types. The first complete example of a song type is underlined.

From Merritt 1985

TABLE 7 from Derrickson 1987 - This table shows the frequency of occurrence of singlets (song types occurring only once in the sample) and more common song types during several breeding stages and situations.

FIG. 1 from Levey et al. 2009 - Response of incubating mockingbirds to intruders approaching the nest on 5 consecutive days. Black points and lines show responses to the same intruder over the first 4 days; gray points and lines show responses to a novel intruder (control) on the fifth day.

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2 Responses to Trilling 22 Birds with One Tone: The Northern Mockingbird

  1. dahvdhbv says:

    very nice work i think mockingbirds are amazing

  2. bellasbirds says:

    Thank you! I agree – they are wondrous birds. We are so lucky to have so many in Texas where I go to school!

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