Ducks, grouse, sandpipers = large eggs, 40% yolk. Shells require lots of calcium & yolk: little effort in nest building. Songbirds = small eggs, 25% yolk: elaborate nests, after they hatch, altricial nestlings stay in nest, precocial chicks leave nest after hatching, longer development in egg allows chicks to hatch mobile & largely self-sufficient. Birds sit on eggs to keep them warm: brood patches = featherless heating pads that keep eggs at 37 c (99 f) Phalaropes males only incubate, only develop brood patches. Female ducks & grouse do all of the incubation. In species where pair bond remains intact, sometimes females do all incubation: after mating, males desert females, e. g. Hummingbirds female only incubation, males desert: many songbirds, female only incubates, but male feeds female and/or guards nest, e. g. Gray jay: female only incubation, male feeds female on nest (& off nest: e. g. House finch: female incubates, male feeds female on nest: e. g.