We studied how male fifteen-spined sticklebacks, Spinachia spinachia,
vary in paternal competence, whether males advertise their competence
and whether females prefer better fathers. In this species the male al
one provides care for the offspring through nest building, fanning, cl
eaning and protecting the eggs. We found no female preference for larg
er males. Instead, females preferred males that during the subsequent
paternal phase fanned their nests in shorter fanning bouts. Such males
enjoyed a significantly higher hatching success because they fanned m
ore often than males with longer fanning bouts. Males that fanned for
short bouts during the paternal phase were also able to increase their
fin beat rate. Frequent fanning and high fin beat rates may improve t
he flow of oxygen to the eggs. Beat rate may be a condition-dependent
trait, because males that lost more weight were unable to increase the
ir fin beat rate. During courtship, males perform behaviours such as d
isplacement fanning and body shaking. Females preferred males showing
more frequent body shakes during courtship. Body shake frequency corre
lated positively with hatching success, and negatively with mean fanni
ng bout duration during the paternal phase. The results indicate that
female S. spinachia show a preference for direct benefits in terms of
better paternal care, and that males may signal this ability to female
s by shaking their body during courtship. (C) 1998 The Association for
the Study of Animal Behaviour.