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Richard Dawkins discusses this in his book The Greatest Show on Earth: The Evidence for Evolution. The birds, in the aforementioned example Starlings, 'know' which direction to fly and where to be by obeying simple local rules concerning the distance and spacing of other members of the flock in their immediate vicinity, without any global knowledge of the ...


1

Birds, like amphibians, have a third eyelid (the nicitating membrane) that helps them keeps their eyes moistened and allows them to better visualize at high speeds (or, for amphibians, underwater). The glands in birds' eyes allow them to secrete a fluid that is more resistant to evaporation than tears. The membrane also acts as a 'windshield wiper,' with ...


2

I don't know about the specific cues that American robins use for migration. This species is also both a short range (e.g. between states or to lower altitudes) and long range migrant (e.g. Florida & Mexico), so the cues that they use can probably differ between overwintering populations. There are also year-round populations of robins in the US, but ...


15

Birds have a body part known as the nicitating membrane otherwise known as the "third eyelid". This part has become vestigial in humans, where it remains as the plica semilunaris. This image of a masked lapwing clearly shows its nicitating membrane in action, where it covers the eye in a horizontal motion. This is analogous to blinking in humans, and the ...


2

I'm not a specialist in this area, but I would guess that the length of day-light periods compared to night time could be a good trigger. This is quite independent of the weather, is quite constant (even though length of days is known to have changed through over the millions of years past since the formation of earth).


1

My society finch love to eat moist grass particularly orchard grass. Nibbling the whole strand they have chosen back and forth until they are satisfied with the texture and then proceeds to swallow it. They brake most grass into no bigger than an inch in length. I buy the orchard grass from most pet stores. problem with that is the grass has been dried. not ...



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