Pied Flycatcher (Ficedula hypoleuca) Science Article 6
Incubation maybe stressful because it restricts time for foraging (Walsberg 1983, Murphy and Haukioja 1986). Many bird species in which the females incubate alone, females obtain part of their food from their mates (e.g. Lack 1968, Ricklefs 1974, Lyon and Montgomerie 1985, Lifjeld and Slagsvoid 1986, Nilsson and Smith 1988). This behavior may function to supply the female with energy or essential nutrients, thereby increasing her nest attentiveness and shortening periods away from the nest (e.g. Lifjeld and Slagsvoid 1986, Nilsson and Smith 1988, Smith et al. 1989).
Juan Jose Sanz, The Auk 113(1):249-253, 1996