We are studying sexual selection on the size of the black facial mask of common yellowthroats, a socially monogamous warbler. The mask is an ornamental trait that is found only in males and varies two times in size among individuals.

We have evidence that males with larger facial masks gain two types of reproductive benefits (see Thusius et al. 2001).

First, males with larger masks are more likely to gain a social mate. This is very important as males without social mates are not known to gain extrapair matings. In other words, you can't make up for being a loser at mate attraction by fooling around.

Second, males with larger masks are more likely to sire extra-pair young.

We also know from recent aviary studies that mask size is related to both female choice and male-male competition (see Tarof et al. 2005. Proc. Royal Soc. London B 272: 1121-1127). Radio-tracking indicates that mask size is also related to the extra-territorial forays of both sexes. Females visit neighbors with smaller masks than their own mate, and males visit neighbors with smaller masks than their own (Pedersen et al. submitted).


Outdoor aviary at the UWM Field Station. Picture shows side view. On left is 8 x 24' male-male dominance compartment, in which we examine male-male interactions in relation to ornament size. In the middle (with plywood walls) is one of three 8x8' compartments where males are held during female choice experiments. Females are free to move back and forth in the adjoining compartment (right side of picture; 8x24') and to view each male. The amount of time a female spends in front of each male's compartment is one estimate of female preference for a male.


Marc Pedersen radio-tracking with a hand-held Yagi antenna and Communication Specialists R-1000 receiver.

More recently we have begun to focus on other ornaments, in particular the yellow throat, breast and belly - the "bib". Interestingly, our collaborator, Dr. Corey Freeman-Gallant of Skidmore College, has discovered that male mating success in upstate New York is related to the size of the yellow bib and not related to the size of the facial mask, as we found in Wisconsin. Mating success is not related to size of the bib in Wisconsin.

Thus, there appear to be two different male ornaments that are used differently in Wisconsin and New York. We now have a three year (2004-7) grant from NSF to explore the reasons for these population differences.

If you are a graduate student interested in working on this project please click here for more information.


Collaborators and Current Students:

Dr. Linda Whittingham (UWM)

Dr. Corey Freeman-Gallant (Skidmore College).


Julie Garvin (Ph.D. student). Studying immunocompetence of adults and nestlings in Wisconsin in relation to male ornamentation .

Joan Maurer (M.S. student). Studying parasites of adults in Wisconsin in relation to male ornamentation.

Dan Mitchell (M.S. student). Studying male parental care in relation to male ornamentation (in NY and WI).


Former Students and Post-Docs:



Betsy Abroe (M.S. student; graduated May 2004). Studied sex ratios of broods in relation to male ornamentation.

Dr. Scott Tarof (Ph.D. Queen's Univ., Ontario, 2001). NSERC Post-doctoral Fellow 2002-2003. Aviary Experiments on mate choice and dominance.

Kevin Thusius. M.S. completed May. 2000. Now Eastern Field Coordinator for the Ice Age Park & Trail Foundation, West Bend, WI

THUSIUS, K., K. PETERSON, P.O. DUNN, & L.A. WHITTINGHAM. 2001. Male mask size is correlated with mating success in common yellowthroats. Animal Behaviour 62: 435-446.

THUSIUS, K., P.O. DUNN, K. PETERSON, & L.A. WHITTINGHAM. 2001. Extrapair paternity is influenced by breeding synchrony and density in the common yellowthroat. Behavioral Ecology 12:633-639.

Marc Pedersen (M.S. student). Studyied extra-pair mating tactics in WI using radio-tracking.

Kara Peterson (Whittaker). M.S. completed Dec. 1999, co-supervised with Linda Whittingham

 Now working on a Ph.D. at the University of Washington

PETERSON, K., K. THUSIUS, L.A. WHITTINGHAM, & P.O. DUNN. 2001. Allocation of male parental care in relation to paternity within and among broods of common yellowthroats. Ethology 107: 573-586.