05 June 2010

A Herd of Marsh Wrens

This past week, I was at the Lake Station Mitigation Bank in northwest Indiana. This large wetland created by restoring wetland hydrology through removal of subsurface drainage tiles harbors what must be one of the largest, if not the largest, Marsh Wren (Cistothorus palustris) populations in the state.

The Marsh Wren photograph above is from the Lake County Forest Preserves' Species Database. These secretive but brave and territorial birds are endangered in Indiana. They require emergent marsh habitat; at the Lake Station Mitigation Bank, Hybrid Cattail (Typha x glauca) has become abundant in places, and Marsh Wrens have certainly benefited. Below is a video from the Lake Station Mitigation Bank in which you can hear the bubbly songs of several Marsh Wrens (in addition to the conk-la-ree songs of Red-winged Blackbirds, Agelaius phoenicius). The song of the Marsh Wren is described as sounding like a gurgling warble followed by a dry, rattling trill. Unfortunately, the songs in my video don't sound exactly like they did when I was in the field, but this video at least gives an idea of how much they were singing at this site.

Although cattail is generally considered undesirable at mitigation wetlands, it seems there has been a positive correlation between increasing cattail populations and an increasing Marsh Wren population at this site. This introduces the management question of which is more important - a state-listed bird species or a diverse plant community. Prior to development and habitat fragmentation, this likely was not an issue, but now, it seems increasingly likely that we are going to have to make this difficult decision.


Eric Hunt said...

A similar debate rages in San Francisco. The Australian Eucalyptus globulus trees throughout the region support a very large Anna's hummingbird population, to the point that they no longer migrate and remain throughout the year. The E. globulus flowers are very rich in nectar and flower very high off the ground, affording protection from cats, etc. I've watched hummingbirds feed in a grove of Eucalyptus and it's enchanting.

So whenever the question comes up about removing stands of nonnative Eucalyptus and replacing them with the original coastal scrub, the question of what will the birds do is one of the first asked.

Scott Namestnik said...

Interesting, Eric. Our introduction and the establishment of a non-native species has entirely changed the life history of a native species. We have so disrupted the web of life that trying to go back may have a detrimental outcome, at least for some species. That said, it is imperative that the entire conservation community get together on a single page. How will those who don't have conservation ethics ever take the conservation community seriously if one group wants to keep an invasive species for the viability of another native species, while another group wants to remove all non-native species?