kirtland’s warbler 101

December 7, 2005

in Birds, Science

(Previous posts in this series: Introduction, Cowbirds 101, Responses to comments on Cowbirds 101, Problems with Cowbird Control)

I originally intended on making this the last post in this series, but I have been talking to some sources in the Kirtland’s Warbler management and research world, and I’d like to incorporate what I’ve learned into my finale.  This just ended up getting way too long.  I promise to wrap it up…in my next post!  Here I will introduce Michigan’s most famous bird, the endangered Kirtland’s Warbler.

KiwabpfeifferKirtland’s Warbler background

Kirtland’s Warbler is an historically rare bird with very specific nesting requirements: it will only nest in Jack Pines (Pinus banksiana) that are 6 to 24 years old.  And Jack Pines require fire to clear land, enrich poor local soils, and to open their cones and release the seeds.  Further, because the warblers nest on the ground, they nest successfully mostly in Jack Pines growing on a certain type of quick-draining soil known as Grayling sand. This is why the range of this warbler is restricted to the southernmost portion of the range of Jack Pine, found primarily in northern Lower Michigan.  Thus, breeding habitat is rare and ephemeral.

Harold Mayfield, an ornithologist and driving force of early Kirtland’s Warbler conservation, wrote in his Birds of North America account of the species that they “probably survived near extinction for many centuries” due to their specialized habitat requirements.  The warblers may have reached their peak abundance in the late 1800s and early 1900s, aided by the regeneration of forests that were intensively cut during the peak of Michigan’s logging era (1870-1900), and the dramatic forest fires that burned millions of acres during that period.  Concurrently, it is estimated that cowbirds arrived in Michigan about 1850, and by the time of the publication of Michigan’s first detailed bird list, in 1912, they were considered abundant across the state, their spread also facilitated by the changing landscape forged by humans.

Over the last century, logging, forest fragmentation, and fire suppression reduced this already rare habitat. By the mid-1950s, the nesting range of Kirtland’s Warbler was a few counties in the northern Lower Peninsula of Michigan.  The first census of Kirtland’s Warblers counted 432 singing males in 1951.  In 1961, the count was 502.  In 1967, Kirtland’s Warbler was one of the first species to be listed as federally endangered.  Annual surveys began in 1971, when 201 singing male Kirtland’s Warblers were counted.  At that time cowbirds parasitized about 70% of warbler nests.

Cowbird control was initiated the following year. Within a decade, the parasitism rate declined to under 4%.  However, from the onset of cowbird control in 1972, for another ten years beyond the precipitous drop in the cowbird parasitism rate, the population of Kirtland’s Warblers remained about the same (click on graph).

Warbler populations began to take off when a huge chunk of habitat became available to them. In 1980, a prescribed burn in the Mack Lake area went out of control. Recall that Jack Pines are fire-dependent, and warblers prefer Jack Pines that are a minimum of six years old, or about 2 meters tall. When the Mack Lake burn habitat was optimal, around 1990, the warblers moved in, and populations took off.  In 1991, 60% of all singing male warblers were in the Mack Lake burn.

The Mack Lake burn habitat is now becoming too old for Kirtland’s Warblers.  Fortunately, Jack Pines have been planted over the years, providing new habitat for the warblers.  In 2005, the annual census counted 1,451 singing male Kirtland’s Warblers.  From the original six-county core range in Michigan, they were located this year in eleven Lower Peninsula counties and five counties in the Upper Peninsula.  Males have also been found in Wisconsin and Ontario.

My wrap up will touch on the role of cowbird control in warbler recovery, what is next for the program, and some concluding thoughts.

Many thanks to Bryan Pfeiffer at Wings Photography for use of his stunning Kirtland’s Warbler photo.


Cindy M. December 8, 2005 at 11:27 am

great post Nutty and great photo too! It's obvious that crucial habitat is the most important aspect in the continuing recovery of this most special warbler. All of the USFS and USFWS officials I have spoken with have stressed that fact.
Even though spring is your busy season with banding, I hope you can come up for a weekend and we can show you their new strong hold (not too far from Mack Lake).
Awaiting your next post…

Wisecrow December 8, 2005 at 2:51 pm

Hatch:

Since I'm too busy (and lazy) to research it, any idea how this species' unique habitat requirement evolved, how its weird migration pattern developed, and which other warblers it's related to? As I type this, I realize that this is a hell of a lot of info. I should probably look it up myself… Never mind.

TroutGrrrl December 8, 2005 at 11:03 pm

Helluva blog series Nutty. I'm also looking forward to the rest.

Blogs just don't have enough graphs…thanks for your contribution.

Erika April 11, 2006 at 12:11 am

hi. thanx for the info! im using it for a school project. but i do need to know how tall, long and how much it weighs. so if u know just email me. THANx

Comments on this entry are closed.

Previous post:

Next post: