MIDWESTERN RAPTOR POPULATION TRENDS AS DETERMINED BY
FORTY YEARS OF CHRISTMAS BIRD COUNT DATA

Peter C. Petersen1, and Kelly J. McKay2
1Quad City Audubon Society, Davenport, IA 52803.  2Midwest Raptor Research
Fund, Moline, IL 61265.

The Christmas Bird Count Program is sponsored by the National Audubon Society. 
Each year, during a 16-17 day count period, between 1700 and 1800 Christmas
Bird Counts (CBCs) are conducted across North America.  These counts attempt to
census all avian species occurring within a 15-mile diameter circle during a single
day.  The same count circles are conducted each year.  This program represents the
most extensive long-term avian monitoring data collected on a continent-wide
geographic scale.  The Quad City Audubon Society has conducted and compiled
five CBCs since the mid 1950's, each centering on or near the Mississippi River in
eastcentral Iowa and northwest Illinois.  These counts have accumulated 40 years
of data regarding avian populations wintering in the Midwest.  Long-term
information concerning regional raptor population trends is minimal.  Raptors do
not lend themselves well to being monitored during the breeding season by
programs such as the Breeding Bird Survey or Breeding Bird Atlases.  Although
monitoring sites along primary migration corridors have proven to be extremely
effective in monitoring the population trends of various raptor species, few sites
with long-term data exist.  Therefore we decided to use this CBC data set, from a
relatively small geographic area, to examine potential changes in the midwestern
raptor populations since the mid 1950's.  For the purpose of analysis, we added the
total number of individuals for each species from all 5 CBCs.  Additionally, we
combined the data into 5-year increments.  Seven species are characterized by
populations which were stable until the early 1970's to latter 1980's, after which
they have increased fairly steadily.  These species include the sharp-shinned hawk
(Accipiter striatus), cooper's hawk (Accipiter cooperii), red-tailed hawk (Buteo
jamaicensis), american kestrel (Falco sparverius), eastern screech-owl (Otus asio),
barred owl (Strix varia), and bald eagle (Haliaeetus leucocephalus).  In contrast,
populations of the red-shouldered hawk (Buteo lineatus), long-eared owl (Asio
otus), and short-eared owl (Asio flammeus) have declined severely, followed by
greatly reduced populations which have never recovered.  Northern harrier (Circus
cyaneus) and rough-legged hawk (Buteo lagopus) populations have fluctuated
since the mid 1950's, while the great horned owl (Bubo virginianus) has steadily
increased.  In order to truly examine midwestern regional raptor population trends
over the past 40 years, a much larger sample size of CBCs from a broader area of
the Midwest needs to be analyzed.  Nevertheless, we believe the long-term data
accumulated by the extensive CBC program can be used to assist in monitoring
regional raptor population trends over time and across North America.

Keywords: raptors, Christmas Bird Counts, population trends, long-term
monitoring, Mississippi        River

1)   Peter C. Petersen, Quad City Audubon Society, 1108 Jersey Ridge Road,
Davenport, IA  52803.   Phone: (319)355-7051.   FAX: (309)792-5981.   E-mail: not available.
2)   Platform Presentation; not able to convert format.
3)   Not a student paper.