Brood size constrains the development of endothermy in blue tits

Abstract

Altricial birds are unable to maintain body temperature when exposed to low ambient temperatures during the first days after hatching. Thermoregulatory capacity begins to form as postnatal development progresses, and eventually nestlings become homeothermic. Several factors may influence this development at both the level of the individual and the level of the whole brood, but to our knowledge no studies have focused on the effect of brood size per se on the development of endothermy in individual nestlings. We performed cooling experiments on blue tit (Cyanistes caeruleus) nestlings in the field, to study how different experimental brood sizes affected the development of endothermy in individual nestlings and the thermal environment experienced by the whole brood in the nest. Nestlings from all experimental brood sizes showed a decrease in cooling rate as they grew older, but birds from reduced broods showed an earlier onset of endothermy compared with nestlings from enlarged and control broods. This difference manifested during early development and gradually disappeared as nestlings grew older. The thermal environment in the nests differed between treatments during nestling development, such that nest temperature in reduced broods was lower than that in enlarged broods during all days and during nights at the end of the experimental period. We suggest that the development of endothermy in blue tit nestlings is not ontogenetically fixed, but instead may vary according to differences in developmental, nutritional and thermal conditions as determined by brood size.

Harsh conditions during early development influence telomere length in an altricial passerine: Links with oxidative stress and corticosteroids

“…By contrast, nestlings raised in reduced broods were not constrained by these factors and therefore maximized their growth rates. A possible explanation for telomere shortening in these small broods may be explained by possible costs of early thermoregulation (Andreasson, Nord, & Nilsson, ), which may exert a negative impact in telomere shortening. Irrespective of the proximate mechanism, this quadratic effect is interesting as it would suggest the existence of a cellular ageing‐based trade‐off affecting optimal brood size.…”

“…However, given the particularly harsh weather conditions during first broods in the year of study (see above), it is likely that developmental stress levels were higher for first broods, as shown by the higher levels of corticosterone and MDA found in these broods. The reduced telomere length in first broods could thus be explained by the fact that nestlings experienced difficulties to thermoregulate (Andreasson et al., ).…”

How to quantify animal activity from radio‐frequency identification (RFID) recordings

“…Incubation is entirely restricted to females in blue tits (Nord & Nilsson, 2011). Sex roles remain after hatching, with female brooding behavior gradually decreasing as nestlings become endothermic (6-7 days; Andreasson, Nord, & Nilsson, 2016). The method described in this paper was approved and carried out in accordance with the guidelines of the Ethical Committee of the University of Antwerp, Belgium (ID: 2015-64).…”

Decreasing parental task specialization promotes conditional cooperation

“…Third, offspring demand varies over the course of development, with direct consequences for parental tasks. In passerine birds for example, brooding behaviour is exclusively performed by females, but is gradually decreased with nestling age due to enhanced endothermic capacities of the nestlings 19, 20 . Temporal shifts in tasks may thus occur, which likely affect the way how male and female parents coordinate their activities and hence their level of cooperation.…”