lit review: light pollution and singing robins

March 1, 2006

in Science

An interesting paper in the most recent issue of the Condor, the journal of the Cooper Ornithological Society:

Miller, M. W. 2006.  Apparent effects of light pollution on singing behavior of American Robins. Condor 108:130-139.

The author recorded the initiation of the morning song of American Robins in several locations in the eastern U.S. during the breeding seasons in 2002 and 2003.  The sites varied in the intensity of artificial nocturnal light. Two historical data sets were also used for comparison. He found that there was a positive correlation between the time of chorus initiation, relative to civil twilight, and the amount of artificial light.  Robins in areas with a lot of artificial light often began singing during true night, WAY before robins in low-light areas, which still began singing at times comparable to those recorded historically.

I thought the study design left a little bit to be desired. Individual sites were sampled (robin chorus time recorded) only 5 to 19 times. All sampling was done in the April to June time frame, and robins will nest later in the season. I'd like to see this study repeated with a larger sample sizes, at different periods in the breeding season, and in different geographic areas, as well as with different species.

Nonetheless, the results were more than just suggestive — there was a whopping difference in the time robins began to sing in low light areas (less than half an hour before civil twilight) and in high light areas (two or three hours before civil twilight).

Does this have biological implications?  The author suggested some potential possibilities. Robins may have increased productivity if increased light enables them to forage for longer periods, or helps them seek mates. On the other hand, robins singing longer in brightly lit areas may be more vulnerable to predators or have increased energy requirements, and thus have lower survivorship. 

I've often wondered about the consequences of what might amount to sleep-deprivation on urban robins.  Around here in the middle of summer they are often active, or at least vocalizing, until it gets dark, well past 9:30 PM.  Then they begin singing again as early as 3:30 or 4 AM.  During daylight hours, they certainly appear busy with nesting activities.  In light of the current study (pun fully intended), a time-budget analysis and productivity study of robins in rural versus urban areas would be really, um, enlightening.


John March 1, 2006 at 1:38 pm

I have heard robins singing around the midnight to 1 am time frame in my heavily urban – and heavily lighted – neighborhood.

biosparite March 1, 2006 at 5:20 pm

A serious moth student here in urban Houston told me back in 2003 that the strong artificial light in the night-time city had dispalced the initiation of flight time for a particular silkworm species around three hours late to 3 a.m. or so.

Pamela March 1, 2006 at 7:23 pm

Very interesting. Robins are among the first up and the last to go to bed of the diurnal birds in my neighbourhood (a few houses, a couple of street lights and woods and fields that are almost entirely untouched by the resulting light at night). But I have never tracked just how late or how early I've heard them sing–a project for my first post-breeding-atlas breeding season. Thanks!

coturnix March 1, 2006 at 7:57 pm

IMHO, the most dangerous consequence may be the effect of artificial light on the photoperiodic response (measurement of daylength) and a resulting out-of-whack timing of seasonal activities (molting, migration, onset and end of reproduction, etc.). If they perceive very long daylength (or even constant light!) throughout the year, they may attempt to reproduce throughout the year, including in the middle of the winter when the food is scarce and the temperatures too low for the hatchling survival. Eh, well, global warming will take care of that…

Nuthatch March 2, 2006 at 7:20 pm

Great point. Global climate change also threatens to "uncouple" the timing of migrant bird arrivals and nesting and peak food resources (it is believed to have already done so for some species of seabirds). Add that to the weird changes from elevated light levels, plus who knows what from chemicals and pollutants… Ugh.

Home Bird March 5, 2006 at 11:43 pm

Another very interesting post, Nuthatch. I have often wondered about the mockingbirds–you probably don't get many, if any–which are somewhat related to robins. In Maryland, where I lived for 30 years, the mockers sang late at night and early in the morning when on territory, and when any car drove by with headlights on near where they roosted, they woke up an sang for several minutes. This would happen over and over again all night long in my neighborhood. I always worried that this was probably not good for them.

Travis May 4, 2006 at 11:45 pm

Mockingbirds singing at night is covered in a 1988 article in Condor, which is available free online (Derrickson 1988). Singing at night by mockingbirds is common, but usually restricted to unmated males on full moon nights. Artificial lighting does induce singing, even in mated males. Other species have been recorded to sing under artificial lighting including Blackbird, Song Thrush, European Robin, Chiffchaff, Dunnock, Bluethroat, Reed Bunting, and
Nightingale.

Derrickson, K. C. 1988. Variation in repertoire presentation in northern mockingbirds. Condor 90(3):592-606.

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