The quantity-quality trade-off: differential effects of daily food availability times on reproductive performance and offspring quality in diurnal zebra finches.

An abundant food supply is crucial to reproductive performance, as shown by restricted food availability experiments, in small-sized vertebrates including birds. However, whether daily feeding times affect reproduction is largely unknown. The present study investigated the effects of daily food availability times on reproductive performance and quality of eggs and offspring survivors in zebra finches (Taeniopygia guttata). In randomly paired birds kept under a 12 h:12 h light:dark cycle for about 52 weeks, food availability period was restricted to 4 h in the morning [morning food availability (FA) group] or evening (evening FA group), with controls provided with food ad libitum; thus, the daily food deprivation period began after 4 h of food availability in the morning food access group and was continuous with night-time starvation in the evening food access group. Both food restrictions adversely affected reproductive health, as shown by reduced sex steroid and mesotocin levels, but not general metabolism, as indicated by the absence of a difference in thyroxin and triiodothyronine levels. Restricting food access to a 4 h period negatively affected reproductive performance, although there were differences between pairs in the morning and evening FA groups. In particular, there was delayed onset of reproduction and compromised reproductive success in evening FA but not in morning FA pairs; conversely, offspring health was severely compromised in morning FA but not in evening FA group pairs. Furthermore, morning FA group females were in better health, implying a sex bias in parental food provisioning. Overall, we demonstrate trade-off of 'quantity' (number of offspring produced and/or survived) for 'quality' (how healthy offspring were) in response to daily food availability times in zebra finches, which, much like humans, are diurnal and retain the ability to reproduce throughout the year.