Differences In Clutch Size Research Articles

Nest-Site Selection in the MagpiePica picain a High-Density Urban Population of Sofia (Bulgaria)

Abstract. The study was carried out in 1999–2000 in a 405 ha area urban habitat and revealed one of the highest densities (56.8 pairs/km2) for the species. Breeding density was best predicted by the diversity of trees in the plot and was not limited by the presence of tall trees. Birds used 69% of the available tree species and preferentially selected half of them. Taller tree species were preferred to shorter ones and coniferous trees were preferred to broadleaved ones. Nests higher above the ground were more likely to be successful than nests lower down. The greater the nest height, the earlier the Magpies laid eggs and the more fledglings they produced. Pairs nesting in conifers laid earlier than those in broadleaved trees but there were no significant differences in clutch-size, hatching or fledging success between the two habitats. The nest site preference was not well explained by the success rate. Regardless of species, not only tall trees, where success was greater, were preferred but also smaller...

Effect of Supplemental Food on the Breeding of Blue and Great Tits in Mediterranean Habitats

To study the effect of food availability on the onset of reproduction, clutch-size and breeding success in the Blue Parus caeruleus and Great Tit P. major, we experimentally supplied food on parts of a holm oak study site in Mediterranean France during two consecutive years and compared the birds' responses with the natural patterns in holm and downy oak habitats. In the Blue Tit, the mean stage of nest construction was significantly more advanced in the experimental than in the control area in one year; the mean laying date was significantly earlier in the experimental area in both years (difference 6 d in 1986, and 5 d in 1987). Results for the Great Tit showed the same but non-significant trend. For both species, no significant differences in clutch-size were found between experimental and control birds. Supplemental feeding did not increase the Blue Tit's breeding success which was even significantly lower in the experimental than in the control area in 1987. In that year, the experiments apparently advanced laying to the extent that nestlings were present prior to the food peak. We conclude that food availability does not limit laying but rather acts as a stimulus triggering it. However, our results do not exclude that feeding conditions in early spring may also influence the onset of laying by enhancing the physiological condition of the pre-laying female.

The Reproductive Rates of Australian Passerines

The relationships between body weight, clutch size, length of breeding season, breeding frequency, incubation and nestling periods were studied in the Australian passerines. The means of the above factors as well as allometric equations were calculated for all Australian passerines and separately for the four major families (Maluridae, Meliphagidae, Muscicapidae and Ploceidae) and six zones of distribution (all Australia; Bassian; Torresian; Torresian and Bassian; Irian; Eyrean). The mean clutch size of Australian passerines is significantly smaller than that of North African passerines. This is because the old invaders to Australia (e.g. the Meliphagidae, Maluridae and Muscicapidae) have significantly smaller clutches than the new invaders (e.g. Ploceidae and Corvidae). A significant difference in clutch size was found between the Irian and Eyrean zones, supporting an early claim by Kikkawa. Negative correlations were found between body weight and clutch size, length of breeding season and breeding frequency. These indicate that small passerines in Australia tend to have larger clutches and longer breeding seasons and to breed more frequently than larger species. Body weight is positively correlated with both incubation and nestling period, as found for other altricial birds. There are no significant differences in incubation length between the zones, but there are differences among the families. The ecological implications and the possible reasons for the above correlations and differences between the groups are discussed.