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Marine layer and vagrancy

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  • Lethaby, Nick
    All: While the relationship between the presence of a marine layer and fall-outs of migrants and vagrants on the coast is well known, my impression is that not
    Message 1 of 2 , Sep 8 2:44 PM
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      All:

      While the relationship between the presence of a marine layer and fall-outs of migrants and vagrants on the coast is well known, my impression is that not all marine layers are equal. The last week or so in the Santa Barbara area, we've been experiencing a marine layer forming at night and then persisting until about 10-11 AM in the morning but there are only extremely low numbers of migrants around. This is a phenomenon I've noticed before. Conversely we sometimes get obviously fall-out with birds everywhere. Is anyone aware of any studies that relate fall-outs to specific marine conditions such as how thick it is (a factor that I think may be important), how far inland it goes, etc? Also does anyone know a public site to access past records of marine weather conditions to co-relate past fall-outs with weather conditions?

      Nick Lethaby
      805 562 5106
      nlethaby@...



      [Non-text portions of this message have been removed]
    • Daniel S. Cooper
      Nick-- While the relationship between the presence of a marine layer and fall-outs of migrants and vagrants on the coast is well known, It is? I d be
      Message 2 of 2 , Sep 8 9:59 PM
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        Nick--

        "> While the relationship between the presence of a marine layer and fall-outs of
        migrants and vagrants on the coast is well known,"

        It is? I'd be curious to hear others' comments, but my impression is that marine layer has
        very little to do with numbers of birds on the ground in fall migration. Just some random
        thoughts based on conversations with colleagues over the years and my experience here
        in and around L.A.:

        1. The nighttime marine layer with a late morning burn-off is basically the default
        weather condition for the coast here in fall. I'm not sure there are enough clear fall
        mornings on the immediate coast to compare.

        2. Not all coastal sites are the same. Why are the Laguna Rd. tamarisks (Ventura Co.) so
        productive, not just for vagrants, but for migrant #s all fall, while nearby groves are dead?
        Malibu Lagoon and sites at Ballona rarely have more than a couple migrants around in
        fall, regardless of weather. Geographical position of trees along the coast has to be a big
        factor; you can spend all fall checking trees on the Palos Verdes peninsula and see very
        few birds, yet there they are, in a random eucalyptus groves 10 mi. inland. Not just
        coastal topography, but the larger landscape features like rivers and ridges must also play
        a role in what seem like fall-outs. I've noticed at Ballona year after year that migrants
        tend to arrive moving downstream (i.e. west) along the (now-cement) Ballona Creek
        channel toward the coast, landing in landscaped plants along the channel edge, and then
        dispersing into native habitats. Some of the most productive - in terms of numbers - fall
        migrant sites in the L.A. Basin are alongside the L.A. River and somewhat inland, from
        Bette Davis Park in Burbank down to DeForest Park in Long Beach.

        3. Not all coastal migrants are the same - the only warbler species I've seen in waves in
        fall at Ballona, for example, are Yellow-rumps, and I don't suppose that's what you have
        in mind when you're talking fall-outs. They're more facultative migrants (as has been
        shown on the east coast at least).

        4. So are all coastal passerine migrants in Aug./Sept. sort of vagrants? Talking sheer
        numbers, most of the movement through the region seems to be through the mtns. and
        in the desert in both fall and spring, with apparently only rather minor traffic along the
        coast. Rowe and Gallion (1996) looked at routes of Turkey Vultures through the state in
        fall, and found a clear pattern of birds moving south along the western slopes of the
        Sierra Nevada, over the southern Sierra, and down through the Mojave Desert toward the
        Colorado River, stopping to roost at riparian oases en route (sound familiar? - other
        migrants are probably following the same routes). Patten et al.'s Birds of the Salton Sea
        (2005) has an interesting graph on migrant movement "corridors" through southern Calif.,
        but it appears to be based on Patten's "unpubl. data" (which are probably much better
        than mine, but still...). Data in Shuford et al. (2000) Avifauna of the Salton Sea (unpubl.
        report) provides some idea of the magnitude of passerine migrants through the Sonoran
        Desert from banding stations in the Salton trough, but similar data for coastal sites in
        southern Calif. are scarce. [I'd think maybe Palomarin/Farallones (PRBO) or another long-
        term coastal site somewhere might be a good place to start looking for correlations, but
        that's sort of a different system up there, with coastal weather fronts coming in off the
        ocean (our fall winds tend to blow offshore - "Santa Anas").]

        5. The only place I've noticed any correlation btwn. cloud cover per se and migrants along
        the coastal slope in this area has been when the marine layer leaves the tops of hills clear
        in the sun, which seem to draw in migrants; esp. noticeable in the Puente Hills (both
        spring and fall). But then again, maybe birds just tend to land on hilltops...

        Still stumped,

        Dan Cooper
        Los Angeles

        --- In CALBIRDS@yahoogroups.com, "Lethaby, Nick" <nlethaby@...> wrote:
        >
        > All:
        >
        > While the relationship between the presence of a marine layer and fall-outs of migrants
        and vagrants on the coast is well known, my impression is that not all marine layers are
        equal. The last week or so in the Santa Barbara area, we've been experiencing a marine
        layer forming at night and then persisting until about 10-11 AM in the morning but there
        are only extremely low numbers of migrants around. This is a phenomenon I've noticed
        before. Conversely we sometimes get obviously fall-out with birds everywhere. Is anyone
        aware of any studies that relate fall-outs to specific marine conditions such as how thick
        it is (a factor that I think may be important), how far inland it goes, etc? Also does anyone
        know a public site to access past records of marine weather conditions to co-relate past
        fall-outs with weather conditions?
        >
        > Nick Lethaby
        > 805 562 5106
        > nlethaby@...
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >
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