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Re: Wood Thrush Declines



Hi Kendrick

On Wood Thrush declines I have read that they also seem to suffer
mortality from collisions with tall buildings and radio/tv towers. With
the proliferation of wireless towers and such in the last decade do you
see this as a significant contributer to the bird's decline.

Jules Fraytet
Charlotte, NC

Kendrick Weeks wrote:
> 
> It is very hard to understand population declines of
> Neotropical migrants like Wood Thrush because of their
> complex life cycle.  Increases in mortality can occur
> during breeding (nests or adults), both migration
> events, or wintering.  Short term trends can indicate
> punctuated mortality (such as several cold fronts
> during the peak of trans-gulf migration) while long
> term trends can indicate gradual mortality (such as
> increased  domestic animal predation and cowbird nest
> parasitism).  Drought and extremely wet weather has
> been shown to decrease (or increase, depending on the
> species) survivorship  of nests.  Determining causes
> of population declines requires long term monitoring
> not only of numbers, but also a miriad of factors that
> can affect mortality.  Then, complex regression
> techniques must be used to tease out these causes.
> Using only counts of adults makes it difficult to
> determine causation because many factors are
> correlated and there is little data on nest survival
> (see BBIRD at http://pica.wru.umt.edu/BBIRD/).
> Distinguishing between juveniles and adults during
> counts can help but is not practical.
> 
> Acid rain is thought to disrupt calcium uptake in
> birds.  However, for acid rain to affect a couple of
> species is suspect.
> 
> Your later thoughts tend to imply that the drought
> last year and the wet one this year may have resulted
> in a decline of Wood Thrush for this year's count.  I
> think that that explanation is as good as any with the
> limited amount of data at our disposal.  This is what
> the folks at Patuxent are paid to do.  Speculation on
> population trends, short or long term, is just that.
> 
> As a related aside, A PhD student at NCSU was able to
> show increased nesting success of Wood Thrush in the
> Smokies by an experiment that supplemented some
> breeding Wood Thrush with meal worms.  The
> supplemented birds had significantly (statistically)
> greater nesting success than non-supplemented birds.
> The hypothesis goes that, with increased food there is
> increased nest vigilance, nestling feeding and,
> therefore, increased survival.
> 
> By the way, does anyone know where I can get some
> shade grown coffee?
> 
> Kendrick Weeks
> Fuquay Varina
> 
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