The interactive effect of ambient temperature and brood size manipulation on nestling body mass in blue tits: an exploratory analysis of a long-term study

Abstract

Background Relatively few studies have examined the interactive effects of ecological factors on physiological responses in wild animals. Nearly all of them have been short-term investigations that did not include experimental manipulations, limiting our ability to understand how climate change will affect natural populations. Using a 10-year brood size manipulation experiment in wild blue tits (Cyanistes caeruleus), we quantified the impact of weather conditions and brood competition on the body mass and structural size (tarsus length) of nestlings just prior to leaving the nest. Results We found that variation in nestling body mass on day 14 after hatching was explained by an interactive effect between average ambient temperature experienced during nestling period and brood size treatment. Specifically, in control broods nestling body mass was correlated with temperature in a non-linear manner (concave) with the vertex point (maximum body mass) at ca. 13 °C. In contrast, in enlarged broods nestling body mass permanently increased (also non-linearly) as temperature advanced. Conclusions Our results highlight the importance of considering the effects of brood rearing conditions alongside other environmental factors experienced during growth while investigating early-life environmental effects on body condition.

The delayed effect of climatic conditions on pre‐fledging nestling haematocrit in a suboscine species in Patagonia

“…The consequences of climate breakdown on this species' survival is at risk. These results show that in a warming climate, nestling condition will deteriorate (indicated by sub‐optimum haematocrit) and will reduce post‐fledging survival and population persistence, as found in other studies (Facey et al 2020, Brown et al 2021, Arct et al 2022). The rapid progression of climate breakdown threatens bird species essential to their ecosystems around the globe, of which the consequences grow dire.…”

“…We expect haematocrit to be higher in Pucón than Navarino, due to higher ambient temperatures in the former. Based on other field studies (Mainwaring and Hartley 2016, Arct et al 2022), we expect ambient temperature to be the key driver of nestling haematocrit in rayadito nestlings. Furthermore, we expect that haematocrit levels will be determined either on the day haematocrit is collected (16 days after the first hatching [or D16]) or around hatching when nestlings are physiologically more sensitive.…”

“…Insect abundance or food availability are typically measured to assess the impacts on co‐indices of body condition, individual quality and survival in nestlings such as body weight, haemoglobin and haematocrit (Visser et al 2006, Kaliński et al 2015, Arct et al 2022). We therefore expect that food abundance will be important in predicting pre‐fledgling nestling haematocrit.…”

“…This varies in importance in different studies. For example, one study by Arct et al (2022) found that nestling weight and the environmental temperature just after hatching could predict their pre‐fledging weight. Another study by Capilla‐Lasheras et al (2021) found that high rainfall in the first ten days after hatching lowers the number of successful fledglings.…”

“…Interestingly, temperature and precipitation were not collinear in this study as tropical rainforests can maintain consistent temperatures but vary in precipitation. Precipitation was more influential on nestling haematocrit over ambient temperature, because in heavy precipitation, adults could not forage as much and therefore provided less food for nestlings which resulted in lower body weight and haematocrit (Capilla-Lasheras et al 2021, Arct et al 2022. The aforementioned studies show that the timing of climatic conditions are crucial in producing the best offspring and ensuring the best chances for post-fledging survival.…”