Resource allocation between growth and endothermy allows rapid nestling development at low feeding rates in a species under high nest predation

Abstract

Nestling development is among the most energy‐demanding periods of a bird’s lifetime and altricial species require extensive parental energy investment in the form of feeding and heating. In the present study I analyze the relation and trade‐offs between nestling growth, development of thermoregulation and feeding rate in blackcap Sylvia atricapilla, a species suffering from high nest predation. Nestlings were characterized by rapid growth but they achieved only 80% of adult mass prior to fledging. Body mass showed highest relative growth rate before nestlings achieved homeothermy. The onset of endothermy, indicated in day 7, coincided with 90% of nestling fledgling weight, indicating that the two processes are separated in time. A strong negative correlation between feeding rate and growth rate demonstrates that blackcap nestlings develop their bodies under relatively low feeding rates and more feeding is needed for maintenance of body temperature than for body growth. The study indicates high cost of endothermy for parents – endothermic nestlings received over 100% more feedings than ectothermic ones. The findings are discussed in the light of adaptation of the species to high predation risk.

Brood size constrains the development of endothermy in blue tits

“…O'Connor, 1975;Olson, 1992;Visser and Ricklefs, 1993;Pereyra and Morton, 2001;Brown and Downs, 2002;Cheng and Martin, 2012;Wegrzyn, 2013). This trade-off is corroborated by the difference in the ontogeny of endothermic heat production between altricial and precocial chicks: precocial chicks are more mature and have greater thermogenic capacity at hatching, but a slower growth rate compared with altricial nestlings (Ricklefs et al, 1998).…”

“…However, nestlings of altricial species are poikilothermic and have little or no capacity to maintain core body temperature when exposed to temperatures below the thermal neutral zone (TNZ; where the heat produced by basal metabolism is enough to maintain a normothermic body temperature) during the first part of their life Baarendse et al, 2007). A relatively narrow TNZ develops during the first few days post-hatching, but nestlings still decrease metabolic rate and body temperature when exposed to temperatures below thermal neutrality , during which time nestlings are exclusively dependent on parental heat for maintaining body temperature (Ricklefs, 1984;Wegrzyn, 2013). It is not until several days later that they are able to increase metabolic rate in response to sub-neutral temperatures (O'Connor, 1975;.…”

Cuidado materno y estabilidad térmica durante la anidación en Phaethornis longirostris (ermitaño cola larga)

“…Por lo anterior, se ha propuesto que la aparente incapacidad de los polluelos altriciales para producir calor endó-geno (i.e. ectotermos) durante los primeros días después de la eclosión e incluso que retrasen la endotermia, es en realidad una estrategia que les permite invertir todos sus recursos en desarrollarse y cargar el gasto de su estabilidad térmica a los padres (Clavijo-Baque y Bozinovic 2012, Wegrzyn 2013).…”

Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators

“…Another potential cost of begging may be the risk of nest predation induced by begging vocalization that may inadvertently attract the attention of predators. Nest predation is a major source of reproductive failure in birds (Martin , ) and thus it can exert selective pressure on proximate and evolutionary solutions in offspring strategies (Martin , , , Wiklund , Węgrzyn ). Indeed, there is broad evidence that begging calls increase nest predation (Haskell , , Dearborn , McDonald et al .…”

“…A recent study reported that Blackcap nestlings exhibit a series of solutions to enhance their chance of survival in such a risky environment (Węgrzyn ). They grow fast under minimum feeding rates and are able to fledge at only 80% of adult mass, minimizing exposure time to predators.…”