Physiological Stress Mediates the Honesty of Social Signals

Why can't I get more excited about condition-depending signaling in birds? The entire literature leaves me cold for some reason.

We analyzed corticosterone deposited in growing feathers as an integrated measure of hypothalamic-pituitary-adrenal activity in a wild territorial bird, the red grouse Lagopus lagopus scoticus. We manipulated two key, interrelated components, parasites and testosterone, which influence both ornamentation and fitness. Birds were initially purged of parasites, and later challenged with parasites or not, while at the same time being given testosterone or control implants, using a factorial experimental design. At the treatment level, testosterone enhanced ornamentation, while parasites reduced it, but only in males not implanted with testosterone. Among individuals, the degree to which both parasites and testosterone had an effect was strongly dependent on the amount of corticosterone in the feather grown during the experiment. The more stressors birds had experienced (i.e., higher corticosterone), the more parasites developed, and the less testosterone enhanced ornamentation.
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004983