Pairing status of male willow ptarmigan: is polygyny costly to males?

Abstract

Polygyny appears to be beneficial for males, yet comprises less than 20% of all pair bonds formed by male willow ptarmigan,Lagopus lagopus.This study tested whether polygyny was costly to males. Polygynous males defended larger territories than monogamous and unpaired males and were more likely to be adults than males of other pairing status. Pairing status changed throughout the life of some males. Naturally polygynous males were in better body condition in the early part of the breeding season than other male types, and unpaired territorial males had the lowest condition. Naturally polygynous males had a tendency to lose the least amount of body mass over the season. Naturally polygynous and monogamous males had larger combs than males of other pairing status. Polygynous males had higher reproductive success, similar survival and similar future reproductive success compared with monogamous and unpaired territorial males. Even in years of high clutch predation, and accounting for higher levels of extra-pair paternity in the clutches of polygynous males, naturally polygynous males were more successful than other male types. A group of experimentally polygynous males (i.e. they became polygynous because of a male removal experiment) had similar reproductive success to naturally polygynous males, but lower overwinter survival than other male types. These results suggest that naturally polygynous males were older and ‘better’ than other males and this allowed them to defend larger territories and attract more than one female. Males that became polygynous only as a result of our experiment, however, appeared to suffer costs from this increased breeding effort.