Birds of Indian Subcontinent

Continuous Laying by American Coots in Response to Partial Clutch Removal and Total Clutch Loss

Publication Type:Journal Article
Year of Publication:1992
Authors:Arnold, TW
Journal:The Auk
Date Published:1992
ISBN Number:00048038
Keywords:Fulica, Fulica americana, Fulica atra, Rallidae
Abstract:The ability of American Coots (Fulica americana) to produce additional eggs was studied by experimentally removing six eggs from the clutch during laying (while always maintaining at least three eggs in the nest), and by removing entire clutches during laying to force birds to renest. Coots responded to partial (six-egg) clutch removals by laying an average of 11.5 total eggs, which represents a slight though significant increase over the mean control clutch size of 10.5. Despite this modest increase in mean clutch size, there was a pronounced increase in the proportion of coots producing supernormal clutches (i.e. ≥13 eggs; 26% of removal clutches vs. 8% of control clutches). Egg production was not affected by food availability, as coots with access to supplemental food were no more likely to respond to partial clutch removals than were coots from unsupplemented territories. In response to total clutch loss during laying, most coots (99/119; 83.2%) initiated a continuation clutch. Virtually all continuation clutches (92.4%) were initiated within five days (x̄ = 1.5 ± SD of 2.2 days). Continuation clutches were no smaller than normal clutches, even though continuation nesters had produced several previous eggs. In 1990 and 1991, the total number of eggs produced by continuation nesters (all consecutive nests combined) averaged 15.8 ± 8.2 and 12.8 ± 5.2, respectively, compared to 9.8 ± 1.5 and 11.0 ± 2.1 eggs per clutch in initial undisturbed nests. One continuation nester produced a remarkable 35 eggs in 37 days (four consecutive nests plus two parasitic eggs). Neither egg size nor nesting success were reduced among continuation nesters. Collectively, these data provide strong evidence against the egg-formation hypothesis, which has been invoked to explain both clutch- and egg-size variation in American Coots. These data demonstrate that continuation nesting may provide a better means than partial clutch removals of testing egg-formation capabilities in birds.
Short Title:The Auk
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith