Differential response by males and females to manipulation of partner contribution in the great tit (Parus major)

Abstract

Summary1. In birds with bi-parental care, handicapping is often assumed to decrease the amount of parental care of the handicapped partner. We discuss how handicapping could alter the shape of the handicapped bird's survival±eort curve (theoretical curve relating the survival of a parent to its eort) and show that the optimal response could yield a decrease, no response or even an increase in eort of the handicapped bird. 2. Male or female great tits Parus major (L.) were handicapped during the nestling period by clipping a number of feathers in order to study the eects on parental care and body condition. 3. Handicapped males signi®cantly decreased their feeding rates, while handicapped females did not. Condition of handicapped females signi®cantly deteriorated, while condition of handicapped males did not change during the experiment. Females with a handicapped partner fully compensated for their partner's decrease in work rate, while males with a handicapped partner did not show any compensation and even tended to decrease their feeding rates. 4. Using an inverse optimality approach, we reconstructed the theoretical curve relating the survival of a parent to its eort on the basis of the experimental eects. The handicapped male's survival±eort curve appeared to be slightly steeper than that of handicapped females. This suggests that handicapped males suer more from an increase in eort than handicapped females.

Conflict between parents over care

“…This compensation, which is found in many species of bird (but see [24]), shows that parents respond to each other's behaviour. There is also evidence for compensation in the burying beetle Nicrophorus vespilloides [25], an insect in which both parents care for the young.…”

“…feeding rate) so that the total effort of both parents remains the same. The procedure reduced the feeding rate of the manipulated parent in some studies [23,24], but the response of the mate of the manipulated parent varied. In some studies, there was no statistically significant effect on the feeding rate of the mate [24,32], but both increases and decreases have been reported [33,34].…”

“…The procedure reduced the feeding rate of the manipulated parent in some studies [23,24], but the response of the mate of the manipulated parent varied. In some studies, there was no statistically significant effect on the feeding rate of the mate [24,32], but both increases and decreases have been reported [33,34]. The total feeding rate of the manipulated pair was significantly less than that of control pairs in some studies [23,33], but not significantly different in others [32].…”

Asymmetric sexual conflict over parental care in a biparental cichlid

“…(ii) The fitness consequences of starvation may differ qualitatively between sexes and a reduction of care may only be observed in the more strongly affected sex. This was suggested for great tits, Parus major, in which brood care seems to affect male survival more strongly than female survival (Sanz et al 2000). In these birds males reduced care after being experimentally handicapped by feather-clipping and females fully compensated for reduced male care, while males did not increase care after females had been handicapped.…”

“…by experimentally lowered reserves or increased workload, the partner usually compensates for this reduction to some extent (e.g. Aequidens paraguayensis, Mrowka 1982;Sturnus vulgaris, Wright & Cuthill 1989; Nectarinia osea, Markman et al 1995Markman et al , 1996; Parus major, Sanz et al 2000; Charadrius alexandrinus, Szekely & Cuthill 2000; Eretmodus cyanostictus, Grüter & Taborsky 2004).…”