Brown Thrasher - Michigan Breeding Bird Atlas Website

Brown Thrasher (Toxostoma rufum)
In the Upper Peninsula, the Brown Thrasher was
recorded in 270 blocks and 221 townships in
MBBA I, but only 228 blocks and 186
townships in MBBA II. The overall distribution
in the UP in MBBA II has changed little from
the previous survey. This bird is widely
distributed north of Wisconsin, especially in
Menominee, Dickinson, Marquette and Iron
counties. Elsewhere in the UP, the distribution
is clumped with large regions where the species
is apparently absent, presumably because the
“earlier shrub stages of plant succession” they
require are missing (Eastman, 1991).
Breeding Biology
The adage “timing is everything” is certainly
relevant when surveying for the Brown
Thrasher. Males typically return before
females, by mid April or earlier in the SLP
(Bent 1948), to establish territory. On arrival,
they may counter sing with other males in close
proximity. Singing continues from the tallest
available perch to attract females as they begin
to arrive. The song period is not long in
duration (Cavitt and Haas 2000), but at this time
the species is easy to locate, especially when
multiple males are present. Interestingly, males
sing less frequently when competition is lacking
(pers. obs.). Brown Thrashers renew singing
prior to the second brood or following an initial
nest failure. Once nesting starts the male helps
incubate and feed the young (Cavitt and Haas
2000) and the Brown Thrasher becomes much
less conspicuous. It is not until the young
fledge and begin following the adults around for
food that the thrasher again is more easily
located. Clutch size ranges from 2 to 6 eggs and
may vary seasonally and regionally.
Abundance and Population Trends
(Click to view trends from the BBS)
The Brown Thrasher was likely present in
Michigan well before the time of European
settlement. It was present when Sager published
the first state bird list in 1839 and was listed by
each of the authors throughout the rest of the
Raymond J. Adams, Jr.
19 th and 20 th centuries. It undoubtedly
benefitted from the increase in human
settlement and lumbering as suggested by
Gibbs’ report that it “breeds in all half-cleared
localities in LP” (1879). Most of the comments
regarding abundance are vague. Whether you
read Barrows (1912), who said “summer
resident of all parts of the state…most abundant
in the southern half” or Payne (1983) who
described it as “common in the Lower
Peninsula, more local and less common in the
Upper Peninsula”, exactly how common was it
It probably reached its peak abundance in the
late 1800s following forest clearing. There is
little data on actual numbers in Michigan during
the early 20 th century, but in Illinois the Brown
Thrasher declined 74% from 1909 through 1958
(Cavitt and Haas 2000). With the increased use
of pesticides following World War II, there is
every reason to expect that trend continued.
Federal BBS routes from 1966 through 2007
indicate a decline of more than 80% of Brown
Thrasher numbers in Michigan (Sauer et al.
2008), while Kalamazoo County BBS surveys
suggest an 86% drop from 1970 through 2006.
Michigan Breeding Bird Atlas data from 1983-
2008 also indicate a decline. During MBBA I,
there were nearly 4,100 pairs found in over
2,500 blocks, while the MBBA II results total
about 3,500 pairs in 1,845 blocks. Clearly, the
Brown Thrasher is on a downward trend.
Conservation Needs
While the Brown Thrasher is neither threatened
nor endangered, the rapid population decline
over the past 50 to 100 years is cause for alarm.
As with other declining species which occupy
similar habitat or rely on similar food, a number
of hypotheses have been proposed for the
causes. Following the expansion of pesticide
use after World War II, the Brown Thrasher
suffered increased visible mortality as well as
indirect mortality in and around agricultural
operations (Cavitt and Haas 2000). This no
doubt continues today. Collisions are known to
© 2011 Kalamazoo Nature Center