There is a great deal of random variation in bird population and range.
What this means is as with all things in nature there are changes that
occur within the natural system which effect populations and ranges.  These
changes are normal and not due to an outside assignable cause.

It is impossible to draw any valid conclusions without a large data set
which should include 30 years worth of data for a particular location.
  While there is no dispute about this, it is unpopular, even among some
who claim to be doing science, because it does not support the desired
conclusion, and cannot be quickly confirmed using regression based
analysis, which is ill suited to population based studies, nor can it be
done within the time frame of studying for an advanced degree.

That said there is no dispute about anthroprogenic global warming, but it
is not clear how that overall change is effecting the local climate in the
Cleveland region.

A rather long winded introduction to my own anecdotal observation of no
decline and perhaps an increase in Rose-brested Gosbeak numbers this year
in the forests on the Allegheny plateau to the east of Cleveland.  In
forest habitat they are, along with the Wood Thush, very common to
abundant.

I mention the Wood Thrush, because this species has allegedly declined by
50% in the past 30-40 years.  I see no evidence of this, and as Peterjohn
reported, they are to be found anywhere there is complete canopy.

One has to wonder what happened to these woodland species in the mid 19th
century when much of the eastern US was deforested for agriculture and
commercial exploitation of timber resources?

Haans


On Tue, May 27, 2014 at 12:34 AM, Laura Peskin <[log in to unmask]>wrote:

> Though I am a less-than-stellar birder, it seems that I have not heard or
> seen a rose-breasted grosbeak around Cleveland in a great while. At the
> same time I have seen all the other common birds.  Are rose-breasted's
> nesting populations shifting northward due to warming trends ?  I single
> out the grosbeak because until recently it was a constant May/ June singer
> around the yard.
>
> Laura
>
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