The project on Northern Cardinals began in 1991. In the general sense, we are attempting to explain why male cardinals are so brilliantly colored. More specifically, the research focuses on sexual selection, mate choice, and parental care.

Early on, we determined that predation on nests was intense; more than 70% of all cardinal nests are preyed upon. The question of what makes a "safe" nest site was the subject of Filiater, Breitwisch, and Nealen (1994). Our answer was that there is no safe nest site, and we proposed why that might generally be the case for birds.

In the initial studies of parental care, we used two measures: provisioning nestlings and defending eggs and nestlings against predators. We determined that male cardinals provide more feedings to nestlings than do females (Filliater and Breitwisch 1997). We also determined that neither sex strongly defends offspring against predators (Nealen and Breitwisch 1997). We next asked if ornamentation in either males or females predicts level of provisioning and found that this is so for both males and females (Linville, Breitwisch, and Schilling 1998). This suggests that female cardinals are indeed ornamented, although more subtly than are males.

We studied extra-pair fertilizations (EPFs) in cardinals, using DNA fingerprinting techniques, and asked if ornamentation predicts involvement in EPFs. We found there to be a relationship for males, but the pattern is one in which the brightest males suffer a loss of paternity to extra-pair males. We proposed a new hypothesis to explain this pattern (Linville and Breitwisch, in review).

We studied blood parasites to test the "parasite hypothesis" for the evolution of ornamentation. The predictions are that such a highly ornamented species will have a high incidence of parasitism and that the most ornamented individuals will have the lowest relative levels of parasitism. In refuting this hypothesis, we found that cardinals have a low overall incidence of blood parasites and that there is no relationship between ornamentation and incidence of parasitism (Linville and Breitwisch, in review). We plan to continue this work with an examination of other, more directly transmittable parasites.

We took the opportunity offered by the severe winter of 1994-1995 and the consequent fruit shortage to ask if the drastically decreased supply of fruits affected cardinal ornamentation. The birds require carotenoids (the primary source of which is fruit)as the basis for their red plumage color. We found that colors decreased in intensity in the year in question (Linville and Breitwisch 1998), providing the first documentation of this for any species of bird in the wild.

As a side study, we investigated the relationship between cardinals and brown-headed cowbirds. We found that, although female cowbirds remove cardinal eggs from nests, nestling cardinals grow as fast as nestling cowbirds and effectively compete with cowbird nestlings for food (Eckerle and Breitwisch 1997).

In the 1997 breeding season, we plan to study male provisioning of their mates during courtship and incubation in order to test the hypothesis that ornamentation predicts level of mate provisioning. We are also going to test the hypothesis that more ornamented males more diligently guard their mates against extra-pair copulation attempts from other males than do less ornamented males. We will also collect a second season of data on the quality of nests built by females of known ornamentation.

Sources: T.S. Filliater, R. Breitwisch, P.M Nealen, K.P. Eckerle, S.U. Linville., A. Schilling.

References: Condor, Wilson Bulletin, Auk, Animal Behaviour.