Regarding sources of mortality -- A Smithsonian study on catbird nesting
success in this area, comparing two local areas (Takoma Park and Bethesda)
found loss of fledglings was 86% in Takoma (which exceeded population
replacement needs) and about 61% in Bethesda. The difference was due to high
predation of fledglings, primarily by cats, in Takoma.
http://nationalzoo.si.edu/scbi/migratorybirds/research/gray_catbird/default.
cfm

Predation on eggs and fledglings is probably a major impact on locally
breeding species while migrants are probably more vulnerable to things like
collisions and loss of habitat. In fact, loss of migratory "stop-over"
habitat is a very serious issue and not given enough attention -- one reason
we need to protect our parks and nature reserves from over-zealous mowing,
trimming and removal of native food plants and vines because they are not
esthetic, deer damage and invasive plant species. It always annoys me that
local parks, quoting budget limitations, still manage to mow every square
inch of (potential) meadow which have native grasses & wildflowers but they
can't get off their machines long enough to cut down and remove a strangling
porcelain berry or bittersweet vine.

All of these factors are serious threats to birds -- we need to continue to
work on ones which are controllable such as free-ranging non-native domestic
animals, over-lighted buildings, communications towers with flashing red
(rather than strobe) lights and guy-wires, etc. And too much of the wrong
kind of glass...

Gail Mackiernan
Colesville, MD


on 10/10/2010 9:01 PM, Maurice Barnhill at  wrote:

> In the article linked, the author says he "claims" that glass strikes
> are the second-highest "human-caused" source of mortality in birds.  The
> only number he quotes is 1.5% of a population of parrots (granted that
> they are seriously endangered so any loss is important).  The
> high-looking numbers in that article are all percentages of some set of
> species that have had *any* mortality due to glass.
<snip>