Sex-specific patterns of minimal compensation of care during and after short term mate removal in biparental blue tits

Abstract

Early theoretical models predicted that over evolutionary timescales, changes in effort by one biparental parent should result in incomplete compensation by the other. Empirical studies, however, report responses ranging from no compensation through to complete compensation which may mean that parents respond to each other's efforts over short time scales, as predicted by some recent theoretical models. Few studies have examined behavioural changes over short time periods which mimic the onset of reduced effort so we removed one blue tit (Cyanistes caeruleus) parent for 20 min during nestling provisioning. We then quantified the provisioning rates of both parents for 60 min 'pre-removal', the non-removed partner during the 20 min 'removal' period and both parents for 60 min 'post-removal'. When compared to pre-removal, both sexes reduced their provisioning rates during the removal stage and also during the post-removal stage. There were, however, sexspecific provisioning patterns in the hour after the parent was returned because after females were released, males began provisioning at a relatively high rate and then maintained that rate across the hour after removal whereas after males were released, females began provisioning at a low rate but significantly increased thereafter. There was no long term effect on offspring fitness, which probably reflects the short time parents were removed and so we conclude that parents with biparental care adjust their provisioning rates to successfully overcome very short term decreases in care.

Repeatable negotiation rules? Only females show repeatable responses to partner removal in a brood-provisioning songbird

“…This prediction of ‘partial compensation’ has been tested empirically via experimental manipulation of partner's behaviour in a number of bird species [ 12 ]. These studies found substantial variation in the direction and magnitude of this compensatory response (for a summary on bird species see [ 13 ]), attributable to differences in the experimental set-ups [ 12 , 14 ], species [ 13 ], sexes [ 12 , 13 ] and parental tasks [ 15 , 16 ]. However, these studies have mostly explored variation in compensatory behaviour in terms of among-individuals (population mean) responses and have overlooked within-individual variation in responsiveness.…”