b) HOLE NESTERS HAVE MORE EGGS THAN NONHOLE NESTERS IN SAME FAMILY. In British passerines, open cup nesters average clutches of 5.1 while hole-nesters average 6.9 eggs. WHY? A cup may be too conspicuous--all eggs in 1 basket?
c) HABITAT--forest birds have smaller clutches than birds that nest in meadows. There is likely more food in meadows.
d) SOCIAL STRUCTURE-- no pattern! This is kind of surprising. One reason may be that, with no males, females can still fend for young.