Patterns of female nest attendance and male feeding throughout the incubation period in Blue Tits Cyanistes caeruleus

Abstract

Most bird species exhibit biparental care, but the type of care provided by each sex may differ substantially. In particular, during the incubation phase in passerines, females perform most or all of the incubation, while the male cares for the brood indirectly by feeding the female. However, detailed descriptions of this male investment during the incubation period are missing. Here, we quantitatively describe female nest attendance and male incubation feeding throughout the~14-day incubation period in a population of Eurasian Blue Tits Cyanistes caeruleus breeding in nestboxes. Males and females progressively increased their daily activity at the nest over the incubation period. The amount of day-time incubation, measured as the proportion of the active day (time interval between first nestbox exit in the morning and last entry in the evening) a female spent inside the nestbox, varied between 52 and 60% with an average of 55% per day. The frequency of male incubation feeding varied between 0 and 74 times per day with an average of 12 feeds per day. Both male feeding rate and female nest attendance were highest in the morning and declined rapidly throughout the day. Females were more likely to be off the nest during the warmest periods (15-21°C), as expected based on thermal needs of the developing embryos, but also during the coldest periods (2-5°C), presumably due to the energetic needs of the female. This was despite the fact that males fed their females more often at the nest when ambient temperatures were low. Females that received more feeds incubated more and their off-nest bouts were shorter after a feed. The observed variation in female incubation and in male feeding rate was not linked to individual age or to variation in measures of reproductive success. However, direct observations showed that in some pairs a substantial amount of feeding by males occurred outside the nestbox. This suggests that the true male investment might have been underestimated, here and in previous studies.

Diurnal patterns of ambient temperature but not precipitation influence incubation behavior in Great Tits

“…Therefore, the power of detecting differences in incubation behavior was rather low; (2) only the first 8 days of incubation after clutch completion were studied and not the whole period, which usually lasts for 12-15 days (Glutz von Blotzheim and Bauer 1993). In addition, incubation can already begin after the penultimate egg is laid (Haftorn 1981) and (3) we did not collect data on male incubation feeding, which seems to be related to ambient temperature and might affect incubation behavior (Amininasab et al 2016(Amininasab et al , 2017Bambini et al 2019).…”

“…A variety of factors are assumed to affect incubation behavior, e.g., stage of incubation (Álvarez and Barba 2014b;Basso and Richner 2015), clutch size (Thomson et al 1998), predation risk (Conway and Martin 2000b), male feeding behavior (Bambini et al 2019), phenology (Cresswell and McCleery 2003;Simmonds et al 2017) and weather conditions. Birds that employ uniparental incubation face a trade-off between maintaining egg temperature and their own body condition during incubation period, as they have to leave the nest repeatedly (Kluijver 1950) to avoid depleting stored resources (Reid et al 2002).…”

The effects of season, sex, age and weather on population‐level variation in the timing of activity in Eurasian Blue TitsCyanistes caeruleus

“…The female lays on average 10 eggs, usually one each morning. She then incubates the clutch alone, while her mate often provides her with food (Bambini et al 2018). The eggs hatch about 2 weeks after the start of incubation and the nestlings are fed by both parents for about 20 days.…”

What Can We Quantify About Carer Behavior?

“…For care delivered over substantial periods (e.g., incubation, babysitting) the proportion of active time carers spend on care, or the proportion of opportunities during which care occurs, are more suitable metrics than the intervals between care events. A typical way to model effects on proportional care is a logistic (Bambini et al, 2018) or binomial (Clutton-Brock et al, 2000) regression when the proportion is derived from counts, or a beta/Dirichlet regression when it is based on continuous numbers (Douma and Weedon, 2019).…”