Gwinner, H. 1998. The function of herbs in starling nests. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 225 - 226.

European Starlings Sturnus vulgaris add fresh herbs to their dry nest material. The "courtship hypothesis" proposes that carrying greenery into the nest functions to attract females. Consistent with this hypothesis are the following observations: (1) Males but not females carried greenery into the nests (2) Most nest greenery was found at pair formation but ceased with egg deposition. (3) The amount of greenery was positively correlated with the duration of courtship. The "nest-protection hypothesis" proposes that volatile compounds in green plants may, via parasite control, improve the development of nestlings. I exchanged 140 starling nests with artificial nests containing either green herbs or grass. Consistent with this hypothesis, males preferred plants rich in volatiles. Inconsistent with this hypothesis, ectoparasite loads in grass and herb nests were indistinguishable. However, there was a significant difference in body mass and/or haematocrit levels between chicks growing up in herb or grass nests under unfavourable conditions (e.g. high mite load of nests, insufficient feeding or long rains). I conclude that herbs function as courtship tool and also have a direct positive influence on the condition of chicks.

Key words: sexual selection, herbs, courtship, chicks, Sturnus vulgaris

Blaakmeer, K.B. & Komdeur, J. 1998. Parent-offspring conflict over sex-ratio bias in the Seychelles Brush-Warbler. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 226.

Fisher’s equilibrium sex-ratio theory states that if the fitness costs to the parents of one offspring’s sex relative to the other are higher, parents should discount these costs by producing fewer individuals of the more costly sex. In the co-operatively breeding Seychelles Brush-Warbler Bebrornis sechellensis daughters function as helpers-at-the nest while sons typically disperse. Avian mothers are the heterogametic sex and the presence or absence of the W chromosome determines their offspring’s sex. Seychelles Brush-Warbler mothers adaptively modify the sex of their single egg toward the helping sex when living on territories with rich resources where helpers increase parental reproductive success, but toward the dispersing sex when living on territories where resources are scarce and/or no helping benefit accrues. In addition, by modifying offspring sex ratio parents maximise their number of grand offspring. The fitness consequences of sex allocation for parents, male and female offspring have been determined by precise lifetime fitness values (using parenthood analyses).

Key words: primary sex-ratio, sex allocation, co-operative breeding, lifetime fitness

Li, S-H. & Brown, J.L. 1998. Do extra-pair fertilisations benefit female Mexican Jays? In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 226.

Extra-pair fertilisations (EPFs) are common in the Mexican Jay Aphelocoma ultramarina, suggesting that they are advantageous for some individuals of both sexes. One apparent cost of extra-pair fertilisations (EPFs) to females is that cuckolded males feed nestlings less than non-cuckolded fathers. In compensation, however, females can receive both direct and indirect benefits from EPFs. One direct benefit is that EPF broods received feedings from extra-pair fathers, significantly more than from random adult helpers. The net effect of EPFs on feedings is, consequently, negligible. We examined two types of indirect benefit, one depending on female choice of specific individuals, and one, not. To improve offspring quality, females might choose older or more dominant males as EPF fathers. This was not the case. EPF fathers were usually younger than cuckolded fathers were and more subordinate. It may simply be advantageous for a female to mate with any second male to reduce the risk of deleterious homozygosity in all her offspring. This is suggested by our observation that the number of EPF young in small broods is higher than in large broods. It is consistent with the fact that inbred pairs have smaller broods than outbred pairs and the offspring do not survive as well.

Key words: jay, epc, inbreed, mate choice, parental care, Aphelocoma ultramarina

Martin, T.E. & Ghalambor, C.K. 1998. Males helping females during incubation: Required by microclimate or constrained by nest predation? In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 227.

Nest attentiveness (% of time spent on the nest) during incubation represents a parent-offspring conflict; females must balance a trade-off between caring for embryos by staying on the nest versus caring for themselves by getting off the nest to forage. Males can potentially affect this trade-off and increase nest attentiveness of incubating females by feeding females on the nest. Increased nest attentiveness may be required when local microclimate conditions are harsh, and thereby require greater incubation feeding (microclimate hypothesis). Alternatively, incubation feeding may be constrained by risk of attracting nest predators (nest predation hypothesis), which in turn may constrain female nest attentiveness because of energy limitation. Based on several years of study we show that incubation feeding rates are much greater among cavity-nesting than among coexisting open-nesting birds. Under the microclimate hypothesis, the greater incubation feeding rates of cavity-nesting birds generates the prediction that microclimate should be harsher than for open-nesting birds. Our results reject this hypothesis because we found the opposite pattern. Cavity-nesting birds experienced more moderate (less variable) microclimates that were less often below temperatures (i.e., 15 °C) that can negatively impact eggs compared with open-nesting species. By contrast, incubation feeding rates were highly negatively correlated with nest predation both within and between the two nest types, supporting the nest predation hypothesis. Incubation feeding in turn was positively correlated with nest attentiveness. Thus, nest predation may indirectly affect female incubation behaviour by directly affecting incubation feeding by the male.

Key words: nest attentiveness, incubation feeding, hole nesting, male provisioning, indirect effects

Menezes, L.N., Ranvaud, R.D. & Bucher, E.H. 1998. Breeding synchronisation in Eared Dove Zenaida auriculata colonies in south-eastern Brazil. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 227.

Eared doves breed in large colonies of around 1-5 million birds in sugarcane plantations in south-eastern Brazil. Nests are located on the ground, along sugarcane rows. Breeding was studied by checking nests at weekly intervals in 1996 in four randomly chosen plots of 100 square meters. One large, highly synchronised breeding peak was recorded at the end of February reaching densities between 1.0 and 1.5 eggs/m², followed by three regularly spaced subsidiary peaks with amplitudes decaying 50% of the previous peak's density in each successive wave. The time space between peaks was 30 to 35 days, which is the time required for a complete nesting cycle. Our data suggest that strong synchronising forces determine the onset of breeding as well as successive peaks. Subsidiary peaks may result more likely from renesting than from new individuals joining the breeding population. High synchronism has also been recorded in Eared Dove colonies in north-eastern Brazil, but not in central Argentina, suggesting an adaptive response to variable environmental conditions. However, colonial-social interactions cannot be ruled out. This situation offers a unique opportunity for improving our understanding of colonial breeding in doves.

Key words: doves, colonial breeding, Brazil, population, reproduction

Garamszegi, L., Torok, J. & Toth, L. 1998. Seasonal decline in clutch size of the Collared Flycatcher: Environment or female condition? In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 228 - 229.

Constraints causing the seasonal decline in clutch size were investigated in a central European Collared Flycatcher Ficedula albicollis population. The 'environment hypothesis' assumes that seasonal changes in environmental quality lead to a decline in clutch size. According to the 'condition hypothesis' the differences in physiological condition between early and late breeders cause the variation in number of eggs laid. Using five morphological variables of females (reflecting flying ability and body size), age, body mass (reflecting physiological condition), laying date and three reproductive success variables we applied multiple regression analysis. We found (1) A strong correlation between laying date and clutch size. (2) A direct link between age and clutch size. (3) That morphological variables had significant effect on both laying date and clutch size. (4) That neither clutch size nor laying date was determined by the condition variable. Based on these findings we can reject the condition hypothesis. To test the environment hypothesis, we estimated the food supply by caterpillar frass production and foraging time of parents during nestling period. Results suggest that the link between laying date and clutch size is an adaptive answer to the seasonally changing environment.

Key words: flycatcher, Ficedula albicollis, clutch size, environment, physiological condition