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1) Physiological adaptations of Bird migration: There is no mention of the use of protein as a metabolic fuel during avian migration. Recent studies have found that protein catabolism has important implication in endogenous water production to offset hydration stress during endurance flight.

2) Diving in Emperor Penguin: There is no mention of the role of cumulative muscle work in the dive physiology of Emperor penguin. This has enormous implications for our understanding on the factors that effect the decision of breath-holding divers to end their dives.

3) Study techniques in Bird migration: There is no mention of a) wind tunnels and b) Quantitative magnetic resonance (QMR) body composition analyzers. These two techniques are widely used in laboratory based migration studies.

Physiological adaptations in bird migration edits
Article to review: Bird migration

There is no mention of the metabolic adaptations that birds utilize during migration. Although there are many details yet to be elucidated regarding the processes in action, it is clear that changes in fuel storage and metabolic fuel composition (glycogen:protein:fat ratio) have profound implications in sustaining migratory flight. One of the most remarkable adaptations that migratory physiologists are attempting to determine is: how are migratory birds able to deal with incredible water loss rates and deficits during non-stop migratory flight?

Engel et al.

-	Intuitively, Engel and associates show that respiratory evaporative water loss rates increase with water vapour deficit (more dehydrating conditions). However, they show that this trend is particularly profound in flight.

-	Data shows that flight is essentially a dehydrating condition. Respiratory water loss rates at rest are less than 10% of those during flight.

-	Therefore, water balance may be a potentially limiting factor for migratory flight ranges in birds.

Birds catabolize high rates of protein whether in flight or at rest. Bauchinger and McWilliams (2009) showed that passerine birds undergo a drastic mass reduction of protein containing organs and tissues (~60% reduction in liver) during migratory flight. One idea that arose, and is currently being empirically tested, is that protein may be used as a source of endogenous water to offset water deficits.

Jenni and Jenni-Eiermann

-	Jenni and Jenni-Eiermann calculated that for the same amount of energy (KJ), catabolism of protein results in five times more metabolic and bound water than lipid catabolism.

-	They hypothesized a protein for water strategy in which increased protein catabolism may be a metabolic adaptation in order to offset water losses.

The protein for water hypothesis had been difficult to empirically test until recent advances in technology and methodology. The quantitative magnetic resonance (QMR) body composition analyzer made it possible to repeatedly and non-invasively assess changes in lean mass of birds.

Gerson and Guglielmo

-	They demonstrated by flying Swainson’s thrush in a wind tunnel that ambient humidity has a drastic effect on the fuel composition of birds in flight.

-	At lower ambient humidities, or higher evaporative water loss conditions, birds rely on increased lean mass catabolism in order to offset water deficits.

-	They hypothesized that hypertrophy (increased storage) of protein containing tissues, such as digestive organs and muscle, may reflect the only mechanism available for birds to provision water during non-stop migratory flight.

-	birds preparing to cross major ecological barriers, particularly those with low atmospheric humidity (deserts), should store excess lean mass in preparation for departure.

This information is important to share since it is useful in modifying our existing bird flight range models. By understanding the physiological (metabolic) adaptations of birds, we are able to reveal the factors that supplement or constrain migration. This has profound implications for conservation efforts that more than 50% of migratory avian species currently require.

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