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Testing the feeding-niche partitioning hypothesis in the sexually dimorphic blue-footed booby

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Carlos B. Zavalaga (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Steve Emslie

Abstract: The feeding-niche partitioning hypothesis predicts that sexual size dimorphism in birds evolved as a result of disruptive selection between sexes to avoid food competition. I tested this hypothesis on breeding Blue-footed Boobies (Sula nebouxii) on Isla Lobos de Tierra, Perú, where females are 31% heavier than males. Dietary analysis was determined from regurgitations and foraging behavior was examined using dataloggers in 2002 and 2003. Bearing (60 –120o) and mean maximum foraging distances (19 - 54 km), diet composition (>79% Peruvian Anchovies, Engraulis ringens), time of arrival (mainly before dusk), number of trips per day (1 - 2), and proportion of travel time (83 - 89%) was similar between sexes. Females consumed larger (mean = 12.5 ± 1.4 cm) Peruvian anchovies than males (mean = 11.9 ± 1.6 cm), but no differences in size were found in three other prey species. Overall, females brought 1.5 times more food to the nest than males (range of mean of crop mass = 80 - 109 g). A higher number of females than males departed by mid-morning and dives were deeper around noon than at other times. Females dove deeper (mean = 4.5 ± 1.7 m) than males (mean = 3.5 ± 1.5 m). The lack of spatial and temporal segregation as well as similarities in diet composition between sexes may be explained in terms of the flocking behavior of birds at sea. It is also likely that intersexual similarities may be the result of optimal food conditions during the study period. An analysis of maximum dive depth and body mass of males and females revealed that heavier birds attained deeper depths, but the effects of sex per se and body mass were difficult to separate because the studied birds did not overlap in size. Further sex-specific comparisons of diving behavior among individuals of similar size are necessary to elucidate the effects of body mass in promoting feeding segregation in the water column.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Keywords
Blue-footed booby--Peru--Isla Lobos de Tierra, Boobies (Birds)--Diet, Sexual dimorphism (Animals)
Subjects
Blue-footed booby -- Peru -- Isla Lobos de Tierra
Sexual dimorphism (Animals)
Boobies (Birds) -- Diet