08 December 2009

The Precocial -- altricial gradient

(If you need to, look up to which birds these family names (ending with idae) refer to your text or field guide.)

1. completely independent of parental care (Megapodes; mudnesters)
2. follow parents but feed selves (Anseriformes, Scolopacidae, Charadriidae)
3. follow parents but are shown food -- parents peck at food (quail, grouse)
4. follow parents that feed them (Rallidae, Podicipedidae)
5. semiprecocial: down-covered, open-eyed, but stay in nest (Laridae)
6. semialtricial: down-covered, open or closed eyed, can't walk but are fed by parents
7. 100% altricial
factors causing gradient:
1. Predation pressure: precocial nesters are ground nesters
2. Location of nest: tree nesters or cliff esters don't want precocial young
3. Type of food: precocials are ground feeders parents and young feed together if parents have to go away for food, altricial young will be favored. (Many ground-nesting passerines must be fed in high grass, so altricial.)
4. Phylogenetic background: some ground nesters are altricial (ovenbird, waterthrush) but these are relatively recently evolved from genera with altricial young.


Cliff Swallows

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