The role of partial incubation and egg repositioning within the clutch in hatching asynchrony and subsequent effects on breeding success

Abstract

The main mechanism to achieve hatching asynchrony (HA) for incubating birds is to start heating the eggs before clutch completion. This might be achieved through partial incubation and/or early incubation. Even in the absence of incubation behaviour during the laying phase, clutches still experience a certain degree of asynchrony. Recent studies have shown that eggs located in the centre of the nest receive more heat than peripheral ones during incubation. As eggs receiving more heat would develop faster, we hypothesized that HA should be shorter in nests where eggs were moved homogeneously along the centre–periphery space during incubation than in those nests where eggs repeatedly remained in the same locations, either centrally or peripherally. We explored the relative roles of egg repositioning and partial incubation in determining HA in wild birds by (1) removing eggs from 20 Great Tit Parus major nests on the day of laying and replacing them with fake eggs to avoid partial incubation, and returning them when full incubation began; (2) monitoring twice a day the position of each individually marked egg relative to the clutch centre during incubation, and estimating the coefficient of variation of the distances; and (3) determining HA in each nest. Preventing partial incubation reduced HA by 51% days in experimental nests. It also caused negative effects for the incubating females (lengthening the full incubation period) and positive effects for the brood (increasing fledging success). However, our hypothesis about the role of egg repositioning on HA was not supported: all the females moved the eggs with remarkable consistency, generally attaining a coefficient of variation of the distances around 33%, and it was not related to the HA experienced. We therefore conclude that partial incubation is an important factor regulating HA, and females compensate for the potential effects of differential heating by moving the eggs homogeneously within the clutch.

Incubation in a Temperate Passerine: Do Environmental Conditions Affect Incubation Period Duration and Hatching Success?

“…Other factors had important impacts on hatching success. First, hatching success decreased as the incubation period increased, a finding consistent with previous studies of blue tits (Kluen et al, 2011;Nord and Nilsson, 2011), tree swallows (Lombardo et al, 1995), and great tits (Diez-Méndez et al, 2020). These results indicate that while birds may extend incubation to delay hatching so that it coincides better with the peak of food abundance, there is a cost to this strategic decision if it reduces hatching success.…”

The Impact of Weather on the Behavior and Ecology of Birds

“…Other factors had important impacts on hatching success. First, hatching success decreased as the incubation period increased, a finding consistent with previous studies of blue tits , tree swallows , and great tits (Diez-Méndez et al, 2020). These results indicate that while birds may extend incubation to delay hatching so that it coincides better with the peak of food abundance, there is a cost to this strategic decision if it reduces hatching success.…”

Impacts of ambient temperature and clutch size on incubation behaviour onset in a female‐only incubator songbird

“…In this scenario, females would indirectly shorten the full incubation period at increasing temperatures, which contributes to advanced hatching dates and hatching success (Nord & Nilsson 2012, Macdonald et al . 2013, Diez‐Méndez et al, 2020) but also entails higher hatching asynchrony (see below).…”

“…Diurnal incubation behaviour during the egg‐laying period is known to shorten the (full) incubation period (Stenning 1996, Ardia et al . 2006, García‐Navas & Sanz 2011, Vedder 2012, Aldredge 2017, Diez‐Méndez et al, 2020, but see Podlas & Richner 2013). There is also some evidence that nocturnal behaviour might contribute to shortening that period (Lord et al .…”