You can extrapolate from this research to show how climate change and
habitat change increase the challenge for migrating species.
http://www.blackwell-synergy.com/doi/full/10.1111/j.1474-
919X.2007.00704.x
Weather-related mass-mortality events in migrants
I. NEWTON
Ibis 149 (3), 453–467.
Abstract
A major perceived cost of migration in birds is the associated
mortality. This mortality has proved difficult to measure and separate
from mortality during stationary periods of the annual cycle. This
paper reviews some major recorded mortality incidents among migratory
birds attributed to inclement weather and other factors, including: (1)
in-flight losses, caused by storms and other adverse weather en route,
usually over water; (2) unseasonable cold weather soon after arrival in
breeding areas; and (3) unseasonable cold weather before departure from
breeding areas. Cold weather often kills migrants in their breeding
areas, but not the local resident species which can better withstand it
at those times. For migrants, cold and snow act to cut off the food
supply, and can have a major selective effect on the seasonal timing of
migration. Records of in-flight weather-induced mortality, involving up
to hundreds or thousands of birds at a time, have affected mainly small
passerines, but also larger birds, including eagles and swans. Most
occurred in conditions of mist, rain or snow storms, and some involved
nocturnal collisions with illuminated masts and other tall structures.
Records of post-arrival mortality in breeding areas have involved
mainly small insectivores (especially hirundines), but also waders and
waterfowl. Such incidents, associated with cold and snow, have reduced
local breeding densities from the previous year by 25–90%, depending on
species and area, with up to several years required for recovery.
Records of pre-departure mortality on breeding areas have mainly
affected hirundines. Two major incidents in central Europe in September
1931 and 1974 killed hundreds of thousands, or even millions, of
swallows and martins. After the latter incident, House Martin Delichon
urbicum populations in Switzerland the following year were reduced by
an estimated 25–30%. Such climatic extremes that occurred in spring or
late summer in particular parts of the breeding range have been
recorded at approximate mean frequencies of 2–10 per century. Average
daily mortality in many bird species can clearly be much greater during
migration periods than during stationary periods. Despite the heavy
losses of birds on migration, it may be assumed that migration persists
in the long term because the fitness costs (in terms of associated
mortality) are more than offset by the fitness benefits (in terms of
improved overall survival and breeding success) that accrue from
migration.
==============================www.birding-aus.org
birding-aus.blogspot.com
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
=============================
|
