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The Effects of Weather and Lunar Cycle on Nocturnal Migration of Landbirds at Southeast Farallon Island, California

Peter Pyle, Nadav Nur, R. Philip Henderson and David F. DeSante
The Condor
Vol. 95, No. 2 (May, 1993), pp. 343-361
DOI: 10.2307/1369357
Stable URL: http://www.jstor.org/stable/1369357
Page Count: 19
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Effects of Weather and Lunar Cycle on Nocturnal Migration of Landbirds at Southeast Farallon Island, California
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Abstract

Proximal climatic and lunar effects on arrival and departure of nocturnal migrant landbirds at Southeast Farallon Island (SEFI), California, were examined using multivariate and univariate statistics. Predictive models including date, weather and lunar variables were developed for both spring and fall, which accounted for 33-40% of variation in arrival totals and 18-21% of variation in departure proportions. Seasonal, regional, and taxonomic variation in weather- and lunar-migration relationships were assessed and, along with comparisons of arrival and departure patterns, used to differentiate proximal effects on arrival to SEFI, from widespread effects resulting in increased migration volume over California. Low wind speeds, low to moderate visibility, full cloud cover and lack of fog were proximal effects increasing arrival to SEFI, while low wind speeds, low but rising barometric pressure, clear and clearing skies, high visibility, and decreased moonlight (in fall) resulted in increased departure proportions and, presumably, caused higher migration volume over the region. Effects of wind direction and air temperature, although related to synoptic weather-migration relationships, generally had obscure or minimal direct influences on arrival and departure at SEFI. Departure proportion in spring increased with decreased departure proportion the day before, but few other delay effects between weather variables and arrival or departure were found. Seasonal, regional, and taxonomic variation in departure effects were relatively small suggesting that selection of weather-migration strategies has evolved convergently in a diverse group of migrants flying over a region the size of California.

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