Diet of Nestling Willow Flycatchers in Meadows of the Sierra Nevada

Abstract

I used video observations to quantify the diet of nestling Willow Flycatchers (Empidonax traillii) at six nests in two meadows (Middle Perazzo and Lacey) on the eastern slope of the Sierra Nevada, California. Prey fed to the nestlings consisted primarily of Diptera (24%), Odonata (22%), Ephemeroptera (16%), Lepidoptera (12%), and Raphidioptera (12%). Other less abundant taxa in the diet included Orthoptera, Coleoptera, and Hymenoptera. Aquatic insects such as Ephemeroptera and Odonata were fed more commonly at the five nests at Middle Perazzo Meadow, whereas terrestrial insects such as pollinating Diptera, Hymenoptera, Orthoptera, and Raphidioptera predominated at the single nest observed at Lacey Meadow. At Middle Perazzo Meadow nestlings in nests situated closer to the meadow’s edge were fed more Raphidioptera, whereas those in nests farther from the edge were fed more Ephemeroptera and Odonata. Raphidioptera were fed more frequently in the morning and evening, whereas Diptera, Hymenoptera, Lepidoptera, Hemiptera, and Orthoptera were generally more frequently offered in the middle part of the day. Ephemeroptera were most often provided in the afternoon and evening while feedings with Odonata fluctuated little through the day.