| dc.description.abstract | The first part of this thesis investigated the relationship between time
of nesting and body size in Ring-billed Gulls (Larus delawarensis). There
were no significant differences in skeletal measurements among birds from
early, peak, post-peak, and late nesting periods. Discriminant function
analysis failed to classify individuals by overall body size into groups
defined by the periods in which they initiated nesting activities. Body
condition was significantly lower in late-breeding birds compared to those
from other nesting periods. Although there was a direct relationship between
timing of nesting and body condition, no such relationship held with body
size or individual skeletal variables.
The second part of this thesis examined the relationship between body
size and mate preference in Ring-billed Gulls. A total of 16 skeletal measurements
were taken on each bird from 108 mated pairs of gulls. Variance in skull
and bill measures was significantly lower between mates than in randomly generated
pairs. However, correlation coefficients for all single skeletal
characters between mates were low. High correlations were found between mates
in body condition and fresh weight but not in random pairs. A significant
positive correlation existed between overall body size within mated pairs but
not within random pairs.
The results indicate that Ring-billed Gulls mate assortatively on the
basis of body condition and to a lesser degree by overall body size. I
postulate, however, that this assortative mating is not the result of active
choice of similar-sized or quality mates. Ring-bill probably attempt to
obtain the best quality mate possible, but because of the presence of higher quality competitors, actually obtain mates of comparable size and quality. This
type of mate choice would appear as assortative mating in studies undertaken
after mate selection was completed. | |
