species living in cool climates would starve overnight if they didn’t enter torpor (a
voluntary, reversible condition of low body temp. and inactivity)
ex. West Indian hummingbird Eulampis jugularis drops it temp to 18°C-20°C when
resting at night
changes the set point to reduce diff. b/w ambient and body temp., thereby reducing
NRG expenditure to maintain temp.
Countercurrent Heat Exchange
heat moves from warm to cool; eventually temp. equalizes & net mvmt of heat equalizes
conduction of heat esp. from exposed extremities works against maintaining body temp.
a solution is an arrangement of blood vessels in the extremities called coucountercurrent
in this system, blood flowing from the body toward the extremities continuously
encounters blood returning to the body
extremities of birds would be major avenues of he