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Brown Thrasher - Michigan Breeding Bird Atlas Website

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<strong>Brown</strong> <strong>Thrasher</strong> (Toxostoma rufum)<br />

Raymond J. Adams, Jr.<br />

Manistee Co., MI. 6/21/2009 © Darlene Friedman<br />

This species sponsored by<br />

the Audubon Society of Kalamazoo<br />

(Click to view a comparison of <strong>Atlas</strong> I to II)<br />

Anyone familiar with the <strong>Brown</strong> <strong>Thrasher</strong><br />

during the breeding season is well aware of its<br />

pugnacity. This colorful mimid presents a fierce<br />

demeanor when threatened by potential nest<br />

predators, as I learned at an early age. The<br />

<strong>Brown</strong> <strong>Thrasher</strong> readily throws itself at humans,<br />

dogs, snakes and other birds (pers. obs.). This<br />

thrasher is easily identified as few species are<br />

similar in appearance. There are a handful of<br />

thrushes with comparable patterns, but all lack<br />

the long graceful tail and yellow eye. The only<br />

species which might cause confusion is the<br />

similar Long-billed <strong>Thrasher</strong> which overlaps<br />

with the <strong>Brown</strong> <strong>Thrasher</strong> in south Texas. The<br />

<strong>Brown</strong> <strong>Thrasher</strong> breeds from the East Coast to<br />

the Rocky Mountains and from the Canadian<br />

Prairie Provinces and the south edge of the<br />

boreal forest to the Gulf Coast. In winter it<br />

retires to the southern third of the United States<br />

with a few birds overwintering each year into<br />

the northern U.S. This species breeds<br />

throughout <strong>Michigan</strong>, although it is less<br />

common in the Upper Peninsula and rare on Isle<br />

Royale.<br />

Distribution<br />

On careful examination of the <strong>Michigan</strong> atlas<br />

map for the <strong>Brown</strong> <strong>Thrasher</strong>, this species is<br />

widespread in the LP, reported from 73% of the<br />

townships with a near universal distribution in<br />

the southwestern counties. The prevalence of<br />

thrashers in southwestern <strong>Michigan</strong> is<br />

associated with their preference for deciduousmixed<br />

shrub upland, shrubby old field, and<br />

shrub wetland (Eastman 1991). In addition, this<br />

area of the state has extensive farmland<br />

bordered by hedgerows and tree-lined<br />

fencerows, which provide alternative nesting<br />

cover. Elsewhere in the LP, the <strong>Brown</strong><br />

<strong>Thrasher</strong> is fairly uniform in distribution. In the<br />

eastern third of the LP from Lenawee and<br />

Monroe counties all the way to the Straits of<br />

Mackinac, there is a north/south corridor where<br />

this species is sometimes absent. The causes for<br />

these gaps in occurrence are not obvious from<br />

looking at a map. During MBBA I, the <strong>Brown</strong><br />

<strong>Thrasher</strong> was present in every township in<br />

Oakland and Livingston counties. In MBBA II,<br />

this species was unrecorded in 21 townships in<br />

these same two counties. Urbanization, human<br />

population increases, and the accompanying loss<br />

of habitat likely explain losses of <strong>Brown</strong><br />

<strong>Thrasher</strong> in these two counties (and effort<br />

decreased there from 1,739 hours in MBBA I to<br />

901 hours in MBBA II). But distribution gaps<br />

away from large population centers are more<br />

difficult to explain.<br />

© 2011 Kalamazoo Nature Center


<strong>Brown</strong> <strong>Thrasher</strong> (Toxostoma rufum)<br />

In the Upper Peninsula, the <strong>Brown</strong> <strong>Thrasher</strong> was<br />

recorded in 270 blocks and 221 townships in<br />

MBBA I, but only 228 blocks and 186<br />

townships in MBBA II. The overall distribution<br />

in the UP in MBBA II has changed little from<br />

the previous survey. This bird is widely<br />

distributed north of Wisconsin, especially in<br />

Menominee, Dickinson, Marquette and Iron<br />

counties. Elsewhere in the UP, the distribution<br />

is clumped with large regions where the species<br />

is apparently absent, presumably because the<br />

“earlier shrub stages of plant succession” they<br />

require are missing (Eastman, 1991).<br />

<strong>Breeding</strong> Biology<br />

The adage “timing is everything” is certainly<br />

relevant when surveying for the <strong>Brown</strong><br />

<strong>Thrasher</strong>. Males typically return before<br />

females, by mid April or earlier in the SLP<br />

(Bent 1948), to establish territory. On arrival,<br />

they may counter sing with other males in close<br />

proximity. Singing continues from the tallest<br />

available perch to attract females as they begin<br />

to arrive. The song period is not long in<br />

duration (Cavitt and Haas 2000), but at this time<br />

the species is easy to locate, especially when<br />

multiple males are present. Interestingly, males<br />

sing less frequently when competition is lacking<br />

(pers. obs.). <strong>Brown</strong> <strong>Thrasher</strong>s renew singing<br />

prior to the second brood or following an initial<br />

nest failure. Once nesting starts the male helps<br />

incubate and feed the young (Cavitt and Haas<br />

2000) and the <strong>Brown</strong> <strong>Thrasher</strong> becomes much<br />

less conspicuous. It is not until the young<br />

fledge and begin following the adults around for<br />

food that the thrasher again is more easily<br />

located. Clutch size ranges from 2 to 6 eggs and<br />

may vary seasonally and regionally.<br />

Abundance and Population Trends<br />

(Click to view trends from the BBS)<br />

The <strong>Brown</strong> <strong>Thrasher</strong> was likely present in<br />

<strong>Michigan</strong> well before the time of European<br />

settlement. It was present when Sager published<br />

the first state bird list in 1839 and was listed by<br />

each of the authors throughout the rest of the<br />

Raymond J. Adams, Jr.<br />

19 th and 20 th centuries. It undoubtedly<br />

benefitted from the increase in human<br />

settlement and lumbering as suggested by<br />

Gibbs’ report that it “breeds in all half-cleared<br />

localities in LP” (1879). Most of the comments<br />

regarding abundance are vague. Whether you<br />

read Barrows (1912), who said “summer<br />

resident of all parts of the state…most abundant<br />

in the southern half” or Payne (1983) who<br />

described it as “common in the Lower<br />

Peninsula, more local and less common in the<br />

Upper Peninsula”, exactly how common was it<br />

It probably reached its peak abundance in the<br />

late 1800s following forest clearing. There is<br />

little data on actual numbers in <strong>Michigan</strong> during<br />

the early 20 th century, but in Illinois the <strong>Brown</strong><br />

<strong>Thrasher</strong> declined 74% from 1909 through 1958<br />

(Cavitt and Haas 2000). With the increased use<br />

of pesticides following World War II, there is<br />

every reason to expect that trend continued.<br />

Federal BBS routes from 1966 through 2007<br />

indicate a decline of more than 80% of <strong>Brown</strong><br />

<strong>Thrasher</strong> numbers in <strong>Michigan</strong> (Sauer et al.<br />

2008), while Kalamazoo County BBS surveys<br />

suggest an 86% drop from 1970 through 2006.<br />

<strong>Michigan</strong> <strong>Breeding</strong> <strong>Bird</strong> <strong>Atlas</strong> data from 1983-<br />

2008 also indicate a decline. During MBBA I,<br />

there were nearly 4,100 pairs found in over<br />

2,500 blocks, while the MBBA II results total<br />

about 3,500 pairs in 1,845 blocks. Clearly, the<br />

<strong>Brown</strong> <strong>Thrasher</strong> is on a downward trend.<br />

Conservation Needs<br />

While the <strong>Brown</strong> <strong>Thrasher</strong> is neither threatened<br />

nor endangered, the rapid population decline<br />

over the past 50 to 100 years is cause for alarm.<br />

As with other declining species which occupy<br />

similar habitat or rely on similar food, a number<br />

of hypotheses have been proposed for the<br />

causes. Following the expansion of pesticide<br />

use after World War II, the <strong>Brown</strong> <strong>Thrasher</strong><br />

suffered increased visible mortality as well as<br />

indirect mortality in and around agricultural<br />

operations (Cavitt and Haas 2000). This no<br />

doubt continues today. Collisions are known to<br />

© 2011 Kalamazoo Nature Center


<strong>Brown</strong> <strong>Thrasher</strong> (Toxostoma rufum)<br />

be another serious mortality factor. While<br />

stationary objects such as towers and windows<br />

are well known obstacles, automobiles and<br />

trucks cause heavy mortality. During <strong>Atlas</strong><br />

surveys in southwestern <strong>Michigan</strong>, <strong>Brown</strong><br />

<strong>Thrasher</strong> road kills including young were noted<br />

on occasion (pers. obs.). Because this bird is a<br />

short distance migrant, it is less likely to be<br />

exposed to severe weather in migration. Harsh<br />

winters in the south have been known to cause<br />

major impacts. Habitat degradation and loss<br />

may be the greatest problem of all.<br />

Habitat protection may be the most important<br />

management opportunity. Efforts could include<br />

protecting hedgerows, letting fields go fallow,<br />

providing brush cover along agricultural field<br />

edges, and designing housing developments<br />

where portions of the natural areas are salvaged.<br />

Because roadside mortality has become an<br />

issue, finding ways to alter roadsides so that<br />

wildlife is provided greater protection would<br />

help many bird species, not just the <strong>Brown</strong><br />

<strong>Thrasher</strong>. All children deserve the chance to<br />

discover the <strong>Brown</strong> <strong>Thrasher</strong>’s defensive<br />

behaviors for themselves.<br />

Literature Cited<br />

Barrows, W.B. 1912. <strong>Michigan</strong> bird life.<br />

Special Bulletin. <strong>Michigan</strong> Agricultural<br />

College, East Lansing, <strong>Michigan</strong>, USA.<br />

Bent, A.C. 1948. Life Histories of North<br />

American Nuthatches, Wrens, <strong>Thrasher</strong>s,<br />

and Their Allies. U.S. National Museum<br />

Bulletin 195.<br />

Cavitt, J.F., and C.A. Haas. 2000. <strong>Brown</strong><br />

<strong>Thrasher</strong> (Toxostoma rufum). Account 557<br />

in A. Poole and F. Gill, editors. The <strong>Bird</strong>s<br />

of North America. The <strong>Bird</strong>s of North<br />

America, Inc., Philadelphia, Pennsylvania,<br />

USA.<br />

Eastman, J. 1991. <strong>Brown</strong> <strong>Thrasher</strong> (Toxostoma<br />

rufum). Pages 364-365 in R. Brewer, G.A.<br />

McPeek, and R.J. Adams, Jr. The <strong>Atlas</strong> of<br />

<strong>Breeding</strong> <strong>Bird</strong>s of <strong>Michigan</strong>. <strong>Michigan</strong><br />

Raymond J. Adams, Jr.<br />

State University Press, East Lansing,<br />

<strong>Michigan</strong>, USA.<br />

Gibbs, M. 1879. Annotated list of the birds of<br />

<strong>Michigan</strong>. Bulletin of the US Geological<br />

and Geographical Survey of the Territories<br />

5:481-497.<br />

Payne, R.B. 1983. A Distributional Checklist<br />

of the <strong>Bird</strong>s of <strong>Michigan</strong>. Miscellaneous<br />

Publication 164. University of <strong>Michigan</strong><br />

Museum of Zoology, Ann Arbor, <strong>Michigan</strong>,<br />

USA.<br />

Sager, A. 1839. Report of Doctor Abraham<br />

Sager, zoologist of Geological Survey.<br />

House Documents of the State of <strong>Michigan</strong>:<br />

410-421.<br />

Sauer, J.R., J.E. Hines, and J. Fallon. 2008.<br />

The North American <strong>Breeding</strong> <strong>Bird</strong> Survey,<br />

Results and Analysis 1966-2007. Version<br />

5.15.2008. USGS Patuxent Wildlife<br />

Research Center, Laurel, Maryland, USA.<br />

Suggested Citation<br />

Adams, R.J., Jr. 2011. <strong>Brown</strong> <strong>Thrasher</strong><br />

(Toxostoma rufum). In A.T. Chartier, J.J.<br />

Baldy, and J.M. Brenneman, editors. The<br />

Second <strong>Michigan</strong> <strong>Breeding</strong> <strong>Bird</strong> <strong>Atlas</strong>.<br />

Kalamazoo Nature Center, Kalamazoo,<br />

<strong>Michigan</strong>, USA. Accessed online at:<br />

.<br />

© 2011 Kalamazoo Nature Center

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