THE EFFECTS OF WEATHER AND LUNAR CYCLE ON NOCTURNAL MIGRATION OF LANDBIRDS AT SOUTHEAST FARALLON ISLAND, CALIFORNIA

Proximal climatic and lunar effects on arrival and departure of noctur nal migrant landbirds at Southeast Farallon Island (SEFI), California, were examined using multivariate and univariate statistics. Predictiv e models including date, weather and lunar variables were developed fo r both spring and fall, which accounted for 33-40% of variation in arr ival totals and 18-21% of variation in departure proportions. Seasonal , regional, and taxonomic variation in weather- and lunar-migration re lationships were assessed and, along with comparisons of arrival and d eparture patterns, used to differentiate proximal effects on arrival t o SEFI, from widespread effects resulting in increased migration volum e over California. Low wind speeds, low to moderate visibility, full c loud cover and lack of fog were proximal effects increasing arrival to SEFI, while low wind speeds, low but rising barometric pressure, clea r and clearing skies, high visibility, and decreased moonlight (in fal l) resulted in increased departure proportions and, presumably, caused higher migration volume over the region. Effects of wind direction an d air temperature, although related to synoptic weather-migration rela tionships, generally had obscure or minimal direct influences on arriv al and departure at SEFI. Departure proportion in spring increased wit h decreased departure proportion the day before, but few other delay e ffects 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 strate gies has evolved convergently in a diverse group of migrants flying ov er a region the size of California.