Topics

Warblers - West Side verse East Side , Introduced and non-introduced trees and migrating warblers and vireos.....

Jim Chiropolos
 

Warblers - West side verse East side and migrant movement, and thoughts on introduced trees

While birding in my local patches and watching warbler flocks, I think, why is the live oak habitat so close to my home so good for warblers (Townsends and Hermit especially) and vireos (Cassins especially) compared to the west side of the Berkeley Hills- one mile away - and I live on the east side. I have been amazed by how many migrants the live oaks hold during this spring.

As I think about it, I think it comes to vegetation- native verse introduced and the side of the hill.

Using my yard as a case study, my yard features 3 Monterey pine, 3 redwoods, and introduced trees - three privits, figs, a cinnamon tree and a non-native crab apple and the yard is surrounded by live oaks.
I see warblers daily in the morning in the live oaks around the yard. I see them catching caterpillars - if I follow one bird maybe every 2 to 4 minutes, they find a food item. This spring, If I walk the road lined with live oaks by the house, daily I run into multiple warbler, vireo and tanager flocks.

Compare this to the non-live oak habitat in my yard. Occasionally, warblers and the resident chickadees feed in the Monterey pines and Redwoods, but maybe excepting hermit warblers, which like to feed high up in the Monterey pines in the fall, I see maybe 5 percent or less of the migrant passerines foraging in the redwoods and Monterey pines. I never see warblers or vireos in the introduced trees. It must be food related - the introduced must trees sustain none or very limited quantities of caterpillars to fuel these guys.

If one compares the west side and east side the amount of vegetation is equal - the west side Oakland and Berkeley hills are as wooded on the east side live oak Berkeley habitat. But likely over 50 percent to 70 percent of that habitat is non-native trees (guess on my part). I think less birds use the west side of the hills because the introduced trees hold less food than the continuous live oak forest on the east side. Based on my many walks in east side live oak habitat this spring, I think the live oak habitat holds as many warblers as the blue oak woodland in Mitchell Canyon and Black Diamond Mines, but the birds are just harder to find in the love oak habitat.
Also, the live oak habitat does not attract the Nashville warblers and Hammonds flycatchers that migrate further east. I have never seen either of these species on either side of the Berkeley Hills. Do they not like live oaks - too dense? Wrong habitat structure?

I’m curious to know other people’s opinions. I have had lots of time to think about ecosystems on my walks this year.

Good Birding,
Jim Chiropolos, Orinda

Bill Bousman
 

Jim and others,

In Menlo Park, I live in an area with live and valley oaks that have been here for thousands of years I suppose.  When Captain George Vancouver visited San Francisco in the 1790s, he rode by horseback to visit the mission at Santa  Clara and commented on the large oaks he saw in what is now Menlo Park.  The Valley Oaks are deciduous and have new leaves in spring; the Live Oaks are evergreen but often replace their leaves in early spring.  Many pests time their hatching to match the new leaves that are easier to eat, the most famous, perhaps is the oak moth.  In my experience, it is these larvae that bring the birds.  I assume the moths lay their eggs near oaks and so the cycle is repeated.  I doubt that conifers can support this sort of annual cycle.

Bill Bousman
Menlo Park

On 5/3/2020 5:01 PM, Jim Chiropolos wrote:
Warblers - West side verse East side and migrant movement, and thoughts on introduced trees

While birding in my local patches and watching warbler flocks, I think, why is the live oak habitat so close to my home so good for warblers (Townsends and Hermit especially) and vireos (Cassins especially) compared to the west side of the Berkeley Hills- one mile away - and I live on the east side. I have been amazed by how many migrants the live oaks hold during this spring.

As I think about it, I think it comes to vegetation- native verse introduced and the side of the hill.

Using my yard as a case study, my yard features 3 Monterey pine, 3 redwoods, and introduced trees - three privits, figs, a cinnamon tree and a non-native crab apple and the yard is surrounded by live oaks.
I see warblers daily in the morning in the live oaks around the yard. I see them catching caterpillars - if I follow one bird maybe every 2 to 4 minutes, they find a food item. This spring, If I walk the road lined with live oaks by the house, daily I run into multiple warbler, vireo and tanager flocks.

Compare this to the non-live oak habitat in my yard. Occasionally, warblers and the resident chickadees feed in the Monterey pines and Redwoods, but maybe excepting hermit warblers, which like to feed high up in the Monterey pines in the fall, I see maybe 5 percent or less of the migrant passerines foraging in the redwoods and Monterey pines.  I never see warblers or vireos in the introduced trees. It must be food related - the introduced must trees sustain none or very limited quantities of caterpillars to fuel these guys. 

If one compares the west side and east side the amount of vegetation is equal - the west side Oakland and Berkeley hills are as wooded on the east side live oak Berkeley habitat. But likely over 50 percent to 70 percent of that habitat is non-native trees (guess on my part). I think less birds use the west side of the hills because the introduced trees hold less food than the continuous live oak forest on the east side. Based on my many walks in east side live oak habitat this spring, I think the live oak habitat holds as many warblers as the blue oak woodland in Mitchell Canyon and Black Diamond Mines, but the birds are just harder to find in the love oak habitat. 
Also, the live oak habitat does not attract the Nashville warblers and Hammonds flycatchers that migrate further east. I have never seen either of these species on either side of the Berkeley Hills. Do they not like live oaks - too dense? Wrong habitat structure?

I’m curious to know other people’s opinions. I have had lots of time to think about ecosystems on my walks this year.

Good Birding,
Jim Chiropolos, Orinda



    

Wen Hsu
 

At the website of Bringing Back the Natives Garden Tour (this coming Sunday will be the last day for virtual tours this year), Doug Tallamy has two files comparing native plants and exotic plants in the Bay Area as hosts of butterflies and moths. They bear out Jim's observation: Native Oaks rank number 2 in the number of species they host, second to native willows. And exotic species are way behind.
https://www.bringingbackthenatives.net/douglas-tallamy-resources

Wen Hsu
Berkeley