Age differences in night-time metabolic rate and body temperature in a small passerine

Abstract

Spending the winter in northern climes with short days and cold ambient temperatures (T a) can be energetically challenging for small birds that have high metabolic and heat loss rates. Hence, maintaining body temperature (T b) in T a below thermoneutrality can be energetically costly for a small bird. We still know little about how increased heat production below thermoneutrality affects the level at which T b is maintained, and if these patterns are age specific. To test this, we measured subcutaneous body temperature (T s) and resting metabolic rate (RMR) simultaneously in blue tits (Cyanistes caeruleus) during winter nights in T a 's ranging from 25 to − 15 °C. RMR increased below the lower critical temperature (LCT, estimated at 14 °C) and was 6% higher in young (birds in their first winter) compared to old birds (birds in their second winter or older). The higher RMR was also mirrored in higher T s and thermal conductance (C) in young birds, which we suggest could be caused by age differences in plumage quality, likely driven by time constraints during moult. Reduction in nightly predicted T b was modest and increased again at the coldest ambient temperatures, suggesting that either heat retention or heat production (or both) improved when T a reached levels which are cold by the standards of birds in our population. Our results show that levels of heat production and T b can be age specific. Further studies should address age-specific differences on quality, structure, and thermal conductivity of plumage more explicitly, to investigate the role of variation in insulation in age-linked metabolic phenotypes.

Elevation and body size drive convergent variation in thermo‐insulative feather structure of Himalayan birds

“…Montane taxa showed 1) an increase in the proportion of down, and a small but significant increase in relative feather length, with an increase in elevation and 2) a significant decrease in the proportion of the downy region and relative feather length with an increase in body size. Birds show intraspecific variation in feather structure associated with environmental variables (Andreasson et al 2020), a pattern demonstrated along latitudinal (Broggi et al 2005) and elevational axes (de Zwaan et al 2017). Pap et al (2017Pap et al ( , 2020 in a phylogenetic comparative approach, showed that feather structure variables known to vary within species, also vary across species, in association with environmental temperatures in Eurasian temperate birds.…”

Rest-Phase Hypothermia Reveals a Link Between Aging and Oxidative Stress: A Novel Hypothesis

“…For instance, basal metabolic rate seems to decline with increasing age in birds and mammals (see meta-analysis in Elliott et al, 2015), which may hint to a lower body temperature. Lower body temperature with increasing age has been shown in several studies (see review Kelly, 2006;Andreasson et al, 2020) and such a decrease in body temperature with age may be related to the inability to produce more heat or maintain the heat. For instance, changes in body fat with advancing age might explain lower body temperature in elderly humans in comparison to young (Van Someren et al, 2002;Kenney and Munce, 2003;DeGroot and Kenney, 2007), while in birds subcutaneous fatloss could affect insulation and the capacity to maintain heat.…”

Plasticity of mitochondrial function safeguards phosphorylating respiration during in vitro simulation of rest-phase hypothermia

“…One-two days after capture the birds were implanted with a temperature-sensitive PIT tag (BioTherm13, Biomark, Boise, ID, USA) into the intraperitoneal cavity under local anaesthesia (5% lidocaine) as part of a different study. Eight to 34 h later, the birds were put in a 1 L hermetically sealed glass container ventilated with dry air at 400-500 ml / min (recorded using a FB-8 mass flow meter, Sable Systems, Las Vegas, NV, USA) for measurement of resting metabolic rate (RMR; as oxygen consumption recorded in carbon dioxide-free air using a FC-10 oxygen analyser, Sable Systems) and body temperature (recorded using a custom-built multiplexed antennae system from BioMark) in a climate chamber (Weiss Umwelttechnik C180 [Reiskirchen, Germany]) at thermoneutrality (25 °C; n = 20) [13], during a simulated mild winter night (5 °C: n = 19) and during a simulated very cold winter night (−15 °C; n = 19) for 13-15 h. Four birds were measured each night. Mean RMR was 0.36 ± 0.01 W (mean ± s.e.m.…”

“…However, the modest extent of hypothermia means that the little bird in winter can never forego a significant increase in energetically costly heat production to counter winter cold, even when maximally hypothermic (e.g. 15 ).…”