also note that the juvenile or 1st year song sparrows (and many
other passerines) are the
ones doing the majority of the singing this time of year and they are in
what's called the "plastic singing" phase of their song learning cycle.
probably the DHEA is aiding and abetting this behavior but they can't sing
their final crystalized songs without practicing and hearing themselves
sing, this first fall singing ranges from good to VERY wobbly.
Both white crowned sparrow and song sparrow juveniles with apparently
hopelessly wobbly songs will try to shape up their song on the spot if
they hear an adult or an adult playback, sometimes with great results.
There is evidence to
suggest that they are still learning and choosing their final repertoire
during the fall and into the spring. so while they are practicing singing
and trying to
wedge into territories overlapping or on top of adult birds' established
territories, they are stimulating the adults to sing and fight with them
(although some adult males are copacetic with a singing juvenile on their
territory, explaining some of the threesomes) which helps them hear more
local songs.
Bewicks wrens have the same song learning life history and there's a lot
of wren plastic song being sung out there right now.
enough!
On Wed, 4 Oct 2000, Deborah Wisti-Peterson wrote:

>
> hello tweets,
>
> every year, i notice this phenomenon of passerines who sing in the
> autumn months, and every year i promise myself that i will find the
> answer to why they do this. and, of course, every year, i poke around
> in the literature and eventually get distracted by my dissertation
> work and forget about this question.
>
> this year, i asked my advisor this question and here is a paraphrase
> of what he said.
>
> european starlings actually experience an increase in plasma levels
> of testosterone. this is associated with singing and territorial
> behavior, and sure enough, they are singing and claiming next year's
> nest site! winter weather suppresses the european starlings' breeding
> in the seattle area, however, they do actually breed during the winter
> months down south where it is warmer. this is also true for english
> sparrows/house sparrows.
>
> white-crowned sparrows are photorefractory at this time of the year.
> this means that they are incapable of responding to increased daylengths
> with a corresponding increase in gonadal steroid hormones. singing in
> white-crowned sparrows appears to be independent of testosterone,
> although high testosterone levels that are typical of spring and
> early summer do increase singing behavior. additionally, testosterone
> has long been known to "crystallize" bird song, and it also seems to
> contribute to singing of the full song, rather than small scratchy
> pieces of the song.
>
> white-crowned sparrows use song in other interactions beyond breeding.
> the females also sing quite nicely, and the youngsters sing as well.
> song serves to preserve social structure in this species, which spends
> the winters in large flocks that roam around in search of food.
> song is important in establishing and maintaining the dominance-
> subordinant structure of white-crowned sparrow flocks.
>
> song sparrows, a close relative of white-crowned sparrows, have a
> very different life history than white-crowned sparrows and their
> physiology reflects that well. song sparrows do not migrate at all,
> but instead, they stablish and defend winter territories which may
> or may not be the same as their summer breeding territories. song
> sparrows are kind of interesting because their winter territories are
> maintained and defended by either two or three birds, and these
> groups can be any combination of males and females, although it is
> my observation that there is always at least one male in the group.
> the males and females who form these winter-time partnerships may or
> may not breed with each other the following year (or the previous
> year). the exact relationships between these individuals has never
> been investigated, although we do currently possess the technology to
> learn more about the genetic relationships of these birds.
>
> as i alluded to in my previous paragraph, song sparrows are
> territorial in the winter, and they use song to establish and
> maintain their territories. there is a paper in press right now,
> which is part the dissertation of one of my lab-mates (and my advisor)
> that partially elucidates the hormonal mileu that underlies these
> behaviors. i have not yet seen this paper, but i will post the
> reference when it is finally published for those who might be
> interested.
>
> you should know that song sparrows are photorefractory at this
> time of year, as are their cousins, the whote-crowned sparrows.
> this means that their gonadal steroid hormones are at "barely
> detectable" levels at this time.
>
> in my colleagues' upcoming paper, it was found that there is
> another hormone present in significant levels at this time of
> the year. this hormone, dihydroepiandrostenedion (DHEA) is
> probably produced by the adrenal glands and probably also by
> the testes (in the case of male birds) and released into the
> bloodstream. the levels of DHEA are higher at this time of the
> year than in the spring, when the gonadal steroids -- estrogens,
> androgens and progesterones -- are highest.
>
> normally, DHEA is an inert steroid hormone in birds, except at
> certain times of the year when it can be converted into estrogen.
> at this time of the year, the song sparrow's brain contains the
> necessary enzymes needed to make this conversion, which then causes
> the levels of estrogen to rise in very specific regions of the brain.
> those regions are associtated with song. providing extra DHEA or
> estrogen to song sparrows caused them to respond by singing. blocking
> the action of DHEA caused the birds to stop singing.
>
> there other important physiological events that are dependent upon
> this DHEA-to-estrogen conversion, so song is not the only result of
> this, but song is the most obvious result for those who go into the
> field and look for birds.
>
> there are no autumnal peaks in testosterone or estrogen in the plasma
> of these song sparrows. if these peaks occurred, the bird would then
> undergo gonal growth and other physiological changes that are consistent
> with breeding. (these changes are the same as those seen in starlings
> and english sparrows). however, we discovered that DHEA is relatively
> abundant at this time of the year, and its product, estrogen,
> apparently functions in feedback mechanisms in the brain and also
> contributes to autumnal singing in song sparrows.
>
> it is also possible that the same phenomenon that i described
> for song sparrows might also be in effect in american robins, who
> also undergo an autumnal singing phase, accompanied by increased
> aggressive behaviors.
>
> to summarize, there are at least three different mechanisms that
> seem to trigger autumnal singing. first, there is an actual beginining
> of the breeding season in autumn which is suppressed by the inhospitable
> weather seen in northern latitudes. this is seen in european starlings
> and english sparrows. second, there is the as-yet mechanistically
> not understood singing that is used to maintain social status in
> migratory and seasonally flocking species. this is typical of the
> white-crowned sparrows, where females and juveniles also sing. third,
> but certainly NOT last, there is the DHEA-dependent autumnal singing
> that has been partially investigated in song sparrows and which may
> also be shared with american robins.
>
> i hope this has helped a little bit.
>
> regards,
>
> Deborah Wisti-Peterson, PhD Candidate nyneve at u.washington.edu
> Department of Zoology, University of Washington, Seattle, Wash, USA
> Visit me on the web: http://students.washington.edu/~nyneve/
> Life is better when you are reading a good book -- Author Tim Green
>
>
>
>