Little chirps in praise of willows and floods
June 7, 2010 § 29 Comments
[ERRATA: Photo of Least bell’s vireo was previously erroneously attributed to the LA Times. The photographer is Don Sterba, who also was the person to see and identify the bird. Apologies to Mr. Sterba for the error. The LA Times published his photo with credit, the oversight here was mine.]
Two pair of Least bell’s vireo, an endangered willow-loving bird, have set up camp in the vicinity of the Ballona Freshwater Marsh. Thanks to the Friends of Ballona Wetlands blog and the LA Times for getting the word out! The Times piece also touches on the controversy associated with the freshwater marsh and Playa Vista development. I do disagree with the Times’ characterization of the drainage “ditch” Hughes dug. It may have become a drainage ditch, but early USGS maps clearly indicate that Centinela Creek flowed through the land that became Hughes’ airfield, and the landscape there would have been a floodplain and likely transitional freshwater or brackish marsh area, the “ditch” a functioning creek.
The Army Corps disconnected Centinela Creek from its historical outlet, tying it into Ballona Creek near where the 90 Freeway crosses today. What I don’t know is if others prior to the Army Corps had also shunted it away, leaving a historical channel or creating a new one for site drainage-something a wetland or floodplain would need if you were trying to create farmland. The point is lots of “ditches” and “drains” were creeks (Baldwin Hills oil field creeks, Ballona Creek), and these terms conveniently allow us to see them as unnatural, and therefore expendable. In that sense, we are fortunate that Playa Vista created a managed habitat area.
However, man-made, managed systems often lack something natural systems provide: dynamics. Least bell’s vireo are a particularly interesting species from the standpoint of river/creek system dynamics because they are most successful nesting in areas of young to mid-growth trees with thick shrubs – probably about the age class we are seeing at Playa Vista right now. Our natural cycle of El Niño storms generate floods that maintain that zone of youngish trees and herbaceous shrubs by periodically knocking them down in the floodplain. To quote the Point Reyes Bird Observatory:
Early to mid-successional riparian habitat is typically used for nesting by the Least Bell’s Vireo because it supports the dense shrub cover required for nest concealment as well as a structurally diverse canopy for foraging. Vegetation characteristics of riparian stands between five to ten years of age are most suitable for nesting Least Bell’s Vireo (Goldwasser 1981, Kus 1998, RECON 1989, Fish & Wildlife Service 1998).
In other words, floods are good for these little birds – and restoring the dynamic of flooding to our creek and wetland systems will help to support this population with the least effort on our end. On the other hand, keeping people, dogs etc from disrupting the birds while maintaining a suitable age class of riparian habitat at the freshwater marsh will also likely encourage these vireos to be regular inhabitants. Let’s hope so.
My unsurprising take home message is: the more we restore natural processes through floodplain and creek protection & restoration and biotreatment approaches to stormwater management, the sooner these little guys and their beleaguered brethren the Southwestern willow flycatcher, will be off the endangered species list. And this is do-able. For all the potential the site had before Playa Vista, the development does demonstrate that even a dense urban zone with set aside habitat areas can support some important wildlife diversity – a lesson it’s time for us take upstream to creek sites next to existing urban areas.