Answers to Flight Lesson Questions
Gravity DOES pull on helium balloons. But air is denser (heavier) than helium, so gravity pulls air harder than it pulls helium; the air sinks below the helium. The helium floats higher and higher above the heavy air until it gets high enough that the thinning atmosphere has the same density. That's when the helium balloon stops rising.
Let's say a large falcon grabs for a flying bat with its talons and
misses, except one sharp talon slices into the wing. The bat wing,
made of thin skin, needs stitches to hold the skin together until
it heals, but that isn't possible in nature. So even if the bat narrowly
escapes the falcon, if its wing is torn it can never fly again and
will eventually die. If the exact same thing happens to a bird, the
talon will merely slice into feathers, usually just separating them
and messing them up a bit, but the bird can fix that with preening.
Even if some of the feathers are torn out, the bird will quickly grow
Herons eat fish, which have fairly dense bodies with tough outer skin and scales. They kill these fish by striking them HARD with their strong, sharp, dense beaks. Their neck muscles must be strong, and relatively heavy, too. So in flight they pull their heavy neck and beak in, closer to their center of gravity. Cranes eat some frogs, snakes, and other animals, but pick at them rather than striking. For these reasons, neither a crane's beak nor its neck needs to be as dense. This means cranes have little extra weight in front of their center of gravity and can fly the simple way with their neck stretched out, like geese and swans.
Some examples of birds that don't normally tuck in their legs are cranes, herons, loons, and long-legged shorebirds. Bird expert Laura Erickson once watched cranes staging along the Platte River in Nebraska during a frozen spell in March when temperatures were well below zero. Under these extreme conditions, the cranes were tucking in their legs! This was certainly more to keep their feet warm than to make them aerodynamic.