Effects of a short period of elevated circulating corticosterone on postnatal growth in free-living Eurasian kestrelsFalco tinnunculus

Abstract

SUMMARYEnvironmental conditions affect growth and development and, through developmental plasticity, create phenotypic variation. In suboptimal conditions current survival is traded-off against development. Corticosterone, the main glucocorticoid in birds, may be involved in the reallocation of energy from growth to maintenance, but its effect on growth has rarely been investigated in altricial birds under natural conditions in the wild. In free-living Eurasian kestrel Falco tinnunculus nestlings, we artificially elevated corticosterone to stress-induced levels over 2-3 days in the middle of the nestling stage by implanting biodegradable implants, controlling the treatment with a placebo group. We measured the length of primary feather 8, hand length, tarsus length, body mass and subcutaneous fat stores from day 10 to 25. During corticosterone elevation, primary growth of cort-nestlings was significantly reduced to 71% of placebo-nestlings, hand and tarsus growth were significantly reduced to 14% and 26% of placebonestlings, respectively, and body mass increase stopped, while subcutaneous fat-store growth was not affected. Over the following 5 days, primary growth was still significantly suppressed to 84% of placebo-nestlings, while hand, tarsus and body mass growth were back to normal. During the subsequent 4 days, cort-nestlings partly compensated for the lag in body mass by significantly accelerating the body mass increase compared with placebo-nestlings. Before fledging, primary length was 10% shorter, hand and tarsus 5% and 4% shorter and body mass 8.5% lower in cort-nestlings than in placebo-nestlings, while fat score did not differ significantly between the two groups. Thus, we have shown that in free-living, altricial nestlings a few days of elevated plasma corticosterone levels alone, without food restriction, suppressed growth and this could only partly be compensated for afterwards. Feather, bone and body mass growth were reduced to different degrees, indicating that corticosterone had a differential effect on different structures. This demonstrates that corticosterone is probably involved in the control of developmental plasticity.

Effects of developmental conditions on nestling American Kestrel (Falco sparverius) corticosterone concentrations

“…For example, fledgling Magellanic Penguins (Spheniscus magellanicus) showed no difference in baseline or stress-induced CORT across tourist and non-tourist visited areas [51] and Black-legged Kittiwake chicks (Rissa tridactyla) did not differ in their baseline or stress-induced CORT across levels of investigator disturbance [7]. R epeated exposure to stressors may have severe negative consequences on developing young such as suppression of growth [29] and reduced cognition [21] and even influence the probability of survival [4]. Thus the ability to maintain low baseline and stress-induced CORT in the face of environmental perturbations may act to minimize the deleterious effects of CORT on developing kestrels.…”

Experimental relationships between levels of corticosterone in plasma and feathers in a free-living bird

“…The effects of DEX were also more transient because changes in morphometrics from day 7 to day 11 of DEX-treated birds did not differ from those of placebo birds, suggesting compensatory growth (Müller et al, 2009b). We used the DEX treatment to induce negative feedback in the HPA (Westerhof et al, 1994) and expected decreased plasma CORT and CORT f , but these variables did not differ significantly between DEX and control birds, and birds in the CORT+DEX group were statistically similar to birds in the CORT group.…”

Pre- and post-natal stress in context: effects on the stress physiology in a precocial bird

“…This result was unexpected as stressful experiences often depress growth in the short-term (Eriksen et al, 2003;Hayward and Wingfield, 2004;Saino et al, 2005;Janczak et al, 2006;Spencer and Verhulst, 2007;Müller et al, 2009;Spencer et al, 2009). Studies of pre-natal stress have also suggested that males are more affected than females (Love et al, 2005;Hayward et al, 2006;Love and Williams, 2008).…”