Flight at Low Ambient Humidity Increases Protein Catabolism in Migratory Birds

Abstract

Although fat is the primary fuel for migratory flight in birds, protein is also used. Catabolism of tissue protein yields five times as much water per kilojoule as fat, and so one proposed function of protein catabolism is to maintain water balance during nonstop flights. To test the protein-for-water hypothesis, we flew Swainson's thrushes (Catharus ustulatus) in a climatic wind tunnel under high- and low-humidity conditions at 18°C for up to 5 hours. Flight under dry conditions increased the rates of lean mass loss and endogenous water production and also increased plasma uric acid concentration. These data demonstrate that atmospheric humidity influences fuel composition in flight and suggest that protein deposition and catabolism during migration are, in part, a metabolic strategy to maintain osmotic homeostasis during flight.

Ecophysiology of avian migration in the face of current global hazards

“…It has been suggested that protein loss during flight may be explained by a variety of factors, including (i) adaptive changes in the size of flight muscles and digestive organs in order to minimize energy costs and to increase flight range; (ii) the requirement for gluconeogenesis and anaplerosis of Kreb's cycle intermediates; (iii) endogenous protein turnover; and (iv) a source of water during long-distance flight particularly under dehydrating conditions [89]. Prior to migration, a suite of hormonal and behavioural changes occurs that promotes rapid gains in body lipids and hypertrophy of flight musculature.…”

“…For the reconciliation of empirical findings with theoretical models on the physiology of avian flight, including consideration of bird flight under highaltitude conditions, the construction of a hypobaric wind tunnel [89] and advancements in logging physiological data during flight and migration [125 -127] are exciting developments. In the light of the potentially increased environmental challenges imposed upon migrants, these emerging data are of great importance in determining the maximum capacity of flight endurance for long-distance migrants.…”

Flight performance of western sandpipers Calidris mauri remains uncompromised when mounting an acute phase immune response

“…Birds were flown in a recirculating wind tunnel at AFAR (Gerson and Guglielmo, 2011). A fine mesh net was stretched tight across the front of the test section.…”

Intense flight and endotoxin injection elicit similar effects on leukocyte distributions but dissimilar effects on plasma-based immunological indices in pigeons

“…Yet some forms of flight are strenuous and have costs. These costs range from the relatively short-term energetic costs of a quick escape flight (Nudds and Bryant, 2000) to the considerably longer-term costs associated with the physiological reorganization (Piersma and Lindström, 1997;Gerson and Guglielmo, 2011) and increased energy use (Bundle et al, 2007;Sapir et al, 2010;Pennycuick, 1968;Dawson et al, 1983) that characterize migration. Flight can also lead to tissue damage, for example in the form of increased free-radicals and oxidative stress (Costantini et al, 2008;Larcombe et al, 2010) or direct muscle injury and myofilament degradation (Guglielmo et al, 2001;Bordel and Haase, 2000).…”