Date of Award


Document Type


Degree Name

Master of Science


College of Arts and Sciences


Biology, MS

First Advisor

James L. Hayward

Second Advisor

Shandelle M. Henson


Glaucous-winged Gulls (Larus glaucescens) and Western Gulls (Larus occidentalis) hybridize extensively where their ranges meet along the coasts of Washington and Oregon, producing a continuum of phenotypic intergrades between the two parental species. Previous work has shown that hybrids can experience greater reproductive success than parental types by combining adaptive behaviors, such as nest site selection, of both parental species, although success of hybrids may be affected by shifts in the ecotone between marine upwelling and non-upwelling environments. I investigated whether there is a correlation between phenotype, reproductive success, and nest site choice for gulls in Protection Island National Wildlife Refuge, Washington. I examined plumage melanism and bare part coloration in the field to determine a hybrid index for each bird sampled; indices for each member of a sample pair were summed to produce a pair index. Nests were monitored until eggs hatched; nest habitat was recorded as sheltered or unsheltered. Sheltered nests contained larger clutches and exhibited better hatching success but choice of nest habitat was not associated with hybrid index. Pair index was correlated with mass of the third egg of the clutch, with more Western Gulllike pairs producing smaller eggs. However, hybrid index was not significantly correlated with clutch size or hatching success. The distance of an index to the mode of the distribution of indices also was not correlated significantly with clutch size or hatching success; that is, the most abundant phenotypes on the colony were not significantly more or less successful than any other phenotypes.

Subject Area

Glaucous-winged gull--Reproduction., Western gull--Reproduction., Gulls--Washington (State)--Reproduction.

Creative Commons License

Creative Commons Attribution-No Derivative Works 4.0 International License
This work is licensed under a Creative Commons Attribution-No Derivative Works 4.0 International License.