Elevation impacts the balance between growth and oxidative stress in coal tits.

The short favorable period of time available for the growth in seasonal environments could constrain the resources allocation between growth and other life-history traits, and the short-term fitness benefits of increased growth rate may prevail over other functions. Accelerated growth rates have been associated with long-term deleterious consequences (e.g., decreased lifespan), and recently oxidative stress (the imbalance between pro-oxidants generation and antioxidant defenses) has been suggested as a mediator of these effects. Here, we examined the impact of elevation on growth rate and self-maintenance parameters (resting metabolism, oxidative damage, and antioxidant defenses) of coal tit chicks (Periparus ater). We predicted that the shorter favorable season at the higher-elevation site could lead to a reallocation of resources towards growth at the expense of self-maintenance processes. We found that chicks at high elevation grew significantly faster in terms of body mass and body size. Chicks from the high-elevation site presented higher resting metabolism, higher oxidative damage level, but similar antioxidant defenses, compared to low-elevation chicks. Interestingly, the chicks exhibiting the better antioxidant defenses at 7 days were also those with the highest resting metabolic rate, and the chicks that grew at the faster rate within the high-elevation site were those with the highest levels of oxidative damage on DNA. Our study supports the idea that increasing elevation leads to a higher growth rate in coal tit chicks, possibly in response to a shorter favorable season. In accordance with life-history theory, a bigger investment in growth was done at the expense of body maintenance, at least in terms of oxidative stress.

Seasonal variation in energy expenditure and body composition in captive White Storks (Ciconia ciconia).

North Western European populations of White Storks (Ciconia ciconia) appear to have been saved from extinction by settling, i.e. stopping migration. Settled storks exposed to winter conditions must cope with periods of potentially high energy demands that would otherwise be avoided by the migration process. Doubly labeled water (DLW) was therefore used to examine the seasonal variation (summer vs winter) in daily energy expenditure (DEE) and the body composition of adult and immature storks of both sexes. Male White Storks showed a higher DEE over the winter period than in summer compared with females; in particular, immature males exhibited greater energy expenditure in winter than adult males. Thus, the DEE did not significantly differ between summer and winter (except for immature males), reflecting an absence of thermoregulation cost in winter. For both age classes, total body mass increased in winter, which was mainly due to an increase in fat mass. Adult storks were 5% heavier than immature storks. The sexes differed in body mass, with males weighing significantly more than females by 11%. Mean LBM (lean body mass) was 8.5% higher in adults than in immatures, and was 11.5% higher in males compared with females. Between their first and second summers, immatures accumulated a lean body mass to finally reach the same values as adults, indicating a phase of muscle development. The mean fat mass of the storks did not differ between age classes or between sexes. Based on physiological parameters, this study shows that settled White Storks are able to cope with mild winter periods when they are artificially provided with food. In a view to preserve favourable habitats for this species, it is therefore necessary to decide on a plan of action for breeding areas.