Effects Of Asynchronous Hatching Research Articles

Chick Development and Asynchroneous Hatching in the Zebra Finch (Taeniopygia guttata castanotis).

The mode of hatching in birds has important impacts on both parents and chicks, including the costs and risks of breeding for parents, and sibling competition in a clutch. Birds with multiple eggs in a single clutch often begin incubating when most eggs are laid, thereby reducing time of incubation, nursing burden, and sibling competition. In some songbirds and some other species, however, incubation starts immediately after the first egg is laid, and the chicks thus hatch asynchronously. This may result in differences in parental care and in sibling competition based on body size differences among older and younger chicks, which in turn might produce asynchronous development among siblings favoring the first hatchling, and further affect the development and fitness of the chicks after fledging. To determine whether such processes in fact occur in the zebra finch, we observed chick development in 18 clutches of zebra finches. We found that there were effects of asynchronous hatching, but these were smaller than expected and mostly not significant. Our observations suggest that the amount of care given to each chick may be equated with such factors as a camouflage effect of the down feathers, and that the low illumination within the nest also complicates the determination of the hatching order by the parents.

Starting with a handicap: effects of asynchronous hatching on growth rate, oxidative stress and telomere dynamics in free-living great tits.

A trade-off between resource investment into growth rate and body self-maintenance is likely to occur, but the underlying molecular mediators of such a trade-off remain to be determined. In many altricial birds, hatching asynchrony creates a sibling competitive hierarchy within the brood, with first-hatched nestlings enjoying substantial advantages compared to last-hatched nestlings. We used this opportunity to test for a trade-off between growth and self-maintenance processes (oxidative stress, telomere erosion) in great tit nestlings, since resource availability and allocation are likely to differ between first-hatched and last-hatched nestlings. We found that despite their starting competitive handicap (i.e. being smaller/lighter before day 16), last-hatched nestlings exhibited growth rate and mass/size at fledging similar to first-hatched ones. However, last-hatched nestlings suffered more in terms of oxidative stress, and ended growth with shorter telomeres than first-hatched ones. Interestingly, growth rate was positively related to plasma antioxidant capacity and early life telomere length (i.e. at 7 days old), but among last-hatched nestlings, those exhibiting the faster body size growth were also those exhibiting the greatest telomere erosion. Last-hatched nestlings exhibited elevated levels of plasma testosterone (T), but only at day 7. T levels were positively associated with oxidative damage levels and plasma antioxidant capacity, the latter being only significant for first-hatched nestlings. Our results suggest that last-hatched nestlings present a specific trade-off between growth rate and self-maintenance processes, which is possibly driven by their need to compete with their older siblings and potentially mediated by elevated levels of T.

Differential predation of eggs in clutches of Glaucous‐winged Gulls Larus glaucescens

Differential predation of eggs of Glaucous‐winged Gulls Larus glaucescens was studied on Mitlenatch Island, British Columbia. The predation of single eggs from 3‐egg clutches by conspecifics and Northwestern Crows Corvus caurinus was recorded to assess whether the predators selected eggs at random or showed a preference for a specific egg in the laying sequence. It was found that small and light‐coloured eggs, characteristically the last‐laid egg in the clutch, were taken significantly more often than the other two eggs in the clutch. As chicks derived from this third egg are least likely to fledge because of their small size and the effects of asynchronous hatching, the lightness of the third egg is adaptive in that it helps to focus attention on the small egg.

Growth and Sexual Dimorphism of the Boat-Tailed Grackle

-At hatching, male and female Boat-tailed Grackles (Quiscalus major) are similar in size. By day 12, just before fledging, they differ in manus and tarsal lengths, tarsal thickness, and weight, but not in culmen, primary remex 7, and tail lengths. Male and female nestlings attain asymptotic weights of 102.4 g and 65.6 g, respectively, at a rate faster than predicted from the general passerine pattern. Furthermore, these asymptotes are only 54.8% and 65.3%, respectively, of adult weight. The combination of a faster growth rate and an asymptote below adult size means that grackles fledge sooner than would be expected for the general passerine pattern. Clutches of three eggs hatch asynchronously; the hatching of the third chick does not decrease growth rates of the early-hatching chicks. Thirdhatched young fledge at weights significantly below those of early-hatching young. Compared to males hatching from the first or second egg, males from the third egg require several more days to attain sizes larger than females. The pattern of growth represents an important component of an animal’s life history. Bird species differ widely in the rate at which young attain independence and adult size. Much of this variation is correlated with body size (Ricklefs 1968) and, presumably, fitness. For species in which the sexes differ in size, the pattern of growth often differs between sexes. Typically, at hatching, males and females of many size-dimorphic species do not differ significantly in size, but by fledging, one sex is significantly larger (Ricklefs 1968, Newton 1978, Moss 1979, Howe 1979, Fiala 1981). Frequently the smaller sex develops its plumage and motor skills sooner than the larger sex (Holcomb and Twiest 1970, Newton 1978, Moss 1979, Richter 1983). The larger sex may be more variable in growth and take longer to reach adult size (Howe 1979, Richter 1983). Asynchronous hatching leads to a size hierarchy among the nestlings (Howe 1976, Bryant 1978) which influences how the parents feed the nestlings and the nestlings’ subsequent growth. I have found little information about the effects of asynchronous hatching on the development of sexual dimorphism. Boat-tailed Grackles (Quiscalus major) are sexually dimorphic as adults; this dimorphism develops during the nestling period (McIlhenny 1937). I could find no detailed study of their growth. In central Florida, Boat-tailed Grackles typically lay clutches of two or three eggs (Bancroft 1983). Clutches of two, and the first two eggs in clutches of three, usually hatch on the same day, but several hours apart. In clutches of three, the third egg hatches one day later. Relative to adult size, grackles have a short nestling period (13-l 5 days). This suggests that they grow rapidly and/or fledge before they reach adult size. I investigated the development of sexual dimorphism in Boattailed Grackles and examined the effect of brood size and asynchronous hatching on their growth.