Mass Loss in Breeding House Wrens: Effects of Food Supplements

Abstract

Adult passerines commonly lose mass during the course of the breeding cycle. This loss has been ascribed to an energy deficit incurred during nesting, but recently two adaptational hypotheses have been proposed. The first, the wing-loading hypothesis, proposes that adults actively reduce mass in order to increase flight efficiency. The second, the reserve-mobilization hypothesis, proposes that females store reserves during the early stages of the breeding cycle, which they mobilize to sustain them during later stages. We tested these hypotheses by providing food supplements to House Wrens (Troglodytes aedon) breeding on a study area north of Bloomington, Illinois, during the 1990-1992 breeding seasons. Additional food had no effect on mass except late in one season. Females that were given additional food during the late-young stage in 1992 had significantly higher mass than controls, but their mass was not greater than that normally obtained by females not receiving food supplements in other years. We conclude that the results from this experimental study are consistent with the wing-loading hypothesis, and that House Wrens do not lose mass because of an energy deficit or because they mobilize reserves.

Understanding the energetic costs of living in saline environments: effects of salinity on basal metabolic rate, body mass and daily energy consumption of a long-distance migratory shorebird

“…The mean body mass (42.5±2.7g; post-absorptive state) of the captive birds at the end of the saltwater regime was similar to the mean body mass of overwintering dunlins (subspecies alpina) in their main wintering area on the west coast of Africa (42.0±0.5g in the Banc d'Arguin) (Zwarts et al, 1990). It has been suggested that a reduction in body mass may reduce maintenance costs (Freed, 1981;Norberg, 1981;Cavitt and Thompson, 1997;Deerenberg et al, 1998). Although the body mass of free-ranging shorebirds may vary according to several factors such as predation risk (van de Hout et al, 2010) or adverse weather (Yasué et al, 2003), the loss of body mass of dunlins coping with saltwater could be considered as a strategy to reduce the high energy costs of living in a saline environment.…”

Different reproductive tactics in male collared flycatchers signalled by size of secondary sexual character

“…Ekman & Lilliendahl 1993;Gosler 1996), or (ii) they may di¡er in their ability to adaptively reduce wing-loading when feeding o¡spring (Freed 1981;Norberg 1981;Cavitt & Thomson 1997). However, since food is more abundant for collared £ycatchers breeding early in the season (Wiggins et al 1994),`high-risk' individuals should be expected to carry more fat late in the season.…”

Food Supplementation Fails to Reveal a Trade-Off between Incubation and Self-Maintenance in Female House Wrens

“…The quantity of mealworms used was based on the estimate that a 10.6-g adult house wren expends approximately 61 kJ/day during the nestling stage [40], and that mealworms contain 11.59 kJ/g [37]. As another passerine species has an assimilation efficiency for mealworms of 0.65 [41], an adult house wren would need to consume about 8.2 g of mealworms to satisfy its daily energy requirements.…”