Adjusting the timing of hatching to changing environmental conditions has fitness costs in blue tits

Hatching delays in great tits and blue tits in response to an extreme cold spell: a long-term study

“…It is difficult to tell whether hatching delay immense flexibility is a unique feature of great tits and blue tits. Several studies analyzed the potential of tits for adjusting the interval between laying and hatching date and excluding Cresswell and McCleery (2003), all those studies analyze only 1–3 breeding seasons (Monrós et al 1998; Naef-Daenzer et al 2004; García-Navas and Sanz 2011; Kluen et al 2011). Cresswell and McCleery (2003) suggested that birds increase their fitness by synchronizing their production of offspring with a peak of food abundance (in the case of tits, caterpillars are the optimal food for nestlings).…”

“…It is rather difficult to pause the incubation for more than a few hours without losing the clutch (Lee and Lima 2017). Therefore, delays in hatching usually occur when females are faced with a sudden cold spell (García-Navas and Sanz 2011; Kluen et al 2011; Tomás 2015) and may be considered as beneficial, when they allow for better synchronization between food demands of nestlings and the peak of caterpillar availability (Monrós et al 1998; Cresswell and McCleery 2003). Females may also accelerate hatching, by starting incubation before producing their last eggs, when conditions are improving.…”

“…Additionally, laying gaps and hatching delay may be interpreted as a consequence of food shortage or increased costs of thermoregulation during egg laying period (Nilsson and Svensson 1993a, b; Cucco et al 2017). Little is known about the flexibility of the hatching delay (Naef-Daenzer et al 2004; Kluen et al 2011) and since phenotypic plasticity and flexibility of behavior play a major role in adjusting to unpredictable weather conditions in spring, examining their limits may be an important goal for research (Tomás 2015). …”

Hatching date vs laying date: what should we look at to study avian optimal timing of reproduction?

“…However, what (most) birds need to time with the seasonal peak of food availability is the moment of maximum food demand of their nestlings (van Noordwijk et al , Both et al ), which is more tightly related with hatching date than with laying date. After initiating egg laying, birds still have some opportunities to adjust the time of highest food demand (Cresswell and McCleery , Both and Visser , García‐Navas and Sanz , Kluen et al ), as during the several days elapsed between laying of the first egg until hatching, more precise cues will become available to birds in order to make a more accurate match with food availability.…”

A strong genetic correlation underlying a behavioural syndrome disappears during development because of genotype–age interactions

“…Common environmental effects on nestlings' behaviours due to the environment (biotic and abiotic conditions) shared by nestlings were modelled by including the ID of their nest. A reciprocal cross-fostering procedure was carried out where part of the nestlings were swapped between two nests at 2 days post-hatching between 2006 and 2010 (see [40] for a detailed description), and we used the ID for the nest of rearing as the common environment for cross-fostered nestlings. Finally, e is a vector for residual errors, which represents the difference between the trait values observed and the values expected on the basis of the fixed and random effects.…”