Food‐supplementation does not override the effect of egg mass on fitness‐related traits of nestling house wrens

Abstract

Summary1. Cross-fostering experiments have shown that egg mass per se positively aects post-hatching growth and development in passerine birds. In most studies, however, the initial in¯uence of egg mass was not sustained, leading to questions about the importance of egg mass relative to the cumulative eects of environmental factors during the period of post-hatching care. 2. In house wrens, Troglodytes aedon Vieillot, evidence from cross-fostering experiments suggests that food availability mitigates the in¯uence of egg mass on posthatching growth: early in the season, when food was putatively abundant, the initial eect of egg mass was lost as nestlings aged; however, later, when food was putatively scarcer, the eect of egg mass persisted until nestlings left the nest. 3. We tested the hypothesis that abundant food for provisioning nestlings can decouple the relationship between ®tness-related traits of nestlings and the mass of the eggs from which they hatch (`egg-mass override hypothesis') by providing daily mealworm supplements to broods of house wrens. 4. The food supplements did not increase ®nal nestling mass, ®nal nestling tarsus length, growth rate, or survival until nest-leaving in late-season broods, when the hypothesis of food limitation predicts that there should be such an eect. Instead, the food supplements signi®cantly, but only slightly, increased ®nal nestling mass in early-season broods, when food is putatively abundant. 5. The eect of the food supplements on ®nal nestling mass was independent of egg mass. Nestling survival in early-season broods, and ®nal nestling mass and tarsus length in both early and late-season broods signi®cantly increased with increasing egg mass in both experimental and control broods. 6. We propose that food was not limiting during the course of the experiments and that ®nal nestling mass and tarsus length remained positively related to egg mass because nestling growth and development in house wrens is`predetermined' by some component or property of eggs that covaries with egg mass.

Evolution of reproductive life histories in island birds worldwide

“…This indicates a change in reproductive strategy on islands, with investment per young being favoured in relation to number of young produced, confirming previous suggestions [2,8]. Increased investment per young could be important if it improves offspring quality or survival [21,22] particularly in competitive island environments [51]. The pattern of larger eggs could be related also to lower nest predation [52], which is believed to be an important trait of island environments.…”

How effective are maternal effects at having effects?

“…Maternal effects are known to occur in a wide variety of organisms and influence offspring performance (Mousseau & Fox 1998a,b;Heath et al 1999;Styrsky et al 2000) as well as trophic interactions (Fox & Savalli 1998). It has been rare, however, for the population level consequences of maternal effects to be considered (but see Ergon et al 2001;LaMontagne & McCauley 2001;.…”

Covariation between egg size and rearing condition determines offspring quality: an experiment with the alpine swift

“…Finally, we found that the positive relationship between originalegg size and nestling body mass decreased from hatching to half way through the rearing period, as already reported in other altricial birds (Williams 1994; but see Reid and Boersma 1990;Styrsky et al 1999). This probably reflects the fact that at hatching, body mass depends mainly on the amount of energy stored in eggs (larger eggs have larger stores), whereas at later stages body mass also depends on other factors like parental feeding rate or environmental quality (Smith and Bruum 1998;Styrsky et al 1999; but see Styrsky et al 2000). The observation that nestling survival was positively correlated with the size of eggs laid by foster parents indicates that egg size covaries with parental or territory quality as already documented in five other bird species (Amundsen and Stokland 1990;Reid and Boersma 1990;Bolton 1991;Magrath 1992;Risch and Rohwer 2000).…”