The document discusses the physiological aspects of bird migration, focusing on body fat accumulation and thermoregulation. It highlights the role of endocrine glands in regulating metabolism and fat deposition, essential for migratory behaviors, which are influenced by environmental and ecological factors. Additionally, it explains how birds manage thermoregulation during migration, conserving energy and utilizing fat as an efficient fuel source.

1. PHYSIOLOGICAL
ASPECTS OF BIRD
MIGRATION
(Body Fat Accumulation and
Thermoregulation)
Abhijeet Bhattacharya
KSD’s Model College
Dombivali

2. Migration
❑The word Migration has come from the Greek word ‘Migrar’ means
going from one place to another.
❑Migration is a pattern of periodic behavior in which animals travel
from one habitat to another in search of food, better weather
conditions, escape from predators or reproductive needs.
❑ Four thousand species of birds are migratory (40% of total species)
❑Arctic Tern have one of the longest annual migrations of any animal
on Earth. Every year, arctic terns migrate from the Arctic Circle to the
Antarctic Circle—a round-trip journey of about 30,000 kilometers !!

3. ACCUMULATION
OF BODY FAT
Bird Migration

4. Adaptive Obesity
❑Migration, is part of the life cycle and depends on a complex
internal rhythm that affects the whole organism, particularly the
endocrine glands.
❑ Food consumption increases with the onset of autumn,
reaching a peak at the beginning of the migration season.
❑Metabolic patterns usually change prior to migration, and fats
accumulate in the body tissues. (Adaptive obesity)
❑Gonadal development occurs prior to migration and this leads
to the changes in the metabolism in the bird, leading to heavy
deposition of subcutaneous fat.

5. Endocrine Glands involved in Migration
❑These physiological changes, chiefly under the control of the
thyroid gland, are correlated with migratory activity.
❑Variations in metabolism and Gonad development are
controlled by the Pituitary Gland.
❑The Pituitary Gland is influenced by the environmental factors,
such as variations in day length and the intensity of the Sun.
❑Decrease daylight in stimulates the pituitary to produce Prolactin,
CRH and GNRH.

6. Endocrine Glands involved in Migration
❑CRH stimulates Adrenal Gland to produce Corticosterone.
❑GNRH stimulates Gonads to produce steroids like estrogen and
testosterone
❑Prolactin, Corticosterone and steroids like estrogen and testosterone
help the migratory birds to accumulate subcutaneous fat or Visceral
fat.
❑These hormones also make the birds restless. An added trigger to
migrate.

7. Role of Ecological Factors
❑The deposition of fat, for example, are influenced by the Anterior part of
the Pituitary Gland.
❑Pituitary Gland affects all metabolic processes, including development of
the thyroid gland, to prepare the animal physiologically for migration.
❑However, Pituitary and variation in day length are not the only two factors
responsible for migration.
❑Since ecological factors are variable. So one conclude that Pituitary
prepares the bird for migration and proper ecological conditions are
necessary for initiation of migration.
❑Ecological factors can be availability of food or change in the
environmental temperature.

8. THERMOREGULATION
(Bird Migration)

9. Thermoregulation in Migratory Birds
❑Body temperatures of birds range from about 38 °C to 44 °C
(Endotherm)
❑To maintain the high temperature a high amount of energy is
spent (approximately 90% of metabolic energy)
❑Birds can lower their body temperature below the ambient in
order to conserve energy for the flight.
❑If the migratory pathway has high temperature, birds pant and
perform Gular flutter at stop over sites and some birds seek
higher altitudes for flying.

10. Thermoregulation in Migratory Birds
❑If the stop over site has low temperature, birds huddle
together also smaller sized birds avoid flying at night.
❑Some migrating birds are thought to lower their body
temperatures by 8-10 °C at stopover sites during the night,
conserving energy.
❑ The fat stored in the birds provides bulk of the heat to maintain
the body temperature.

11. Advantage of Fats over Protein &
Carbohydrates
Fat is the preferred fuel for migration because the highly reduced nature
and hydrophobicity of fatty acids result in fat providing approximately
eight times more energy per unit wet mass (∼37 kJ g−1) than
carbohydrates or protein (∼4–5 kJ g−1).