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1

Hatching asynchrony and brood reduction in Blue Tits Cyanistes caeruleus may be a plastic response to local oak Quercus robur bud burst and caterpillar emergence

100%
Stenning M. J.
Acta Ornithologica
|
2008
|
tom 43
|
nr 1
97-106
Blue Tits exhibit extreme variation in clutch size and hatching asynchrony, which is the focus of this study. This paper reports an in-depth study of breeding Blue Tits showing that variation in Blue Tit hatching asynchrony can be explained by a number of phenological variables including particularly, date of bud burst in the local oak tree, which signals caterpillar emergence (34%), also date of first egg (14%) and female weight (8%). Hatching asynchrony explained 9% of the variation in brood mortality in this southern English population. Early incubation relative to clutch completion (incubation asynchrony) in Blue Tits explained 85% of the variation in hatching asynchrony, differs between years and advanced hatching in early and fledging in late laid eggs. Consequently, because fledging is usually synchronous, hatching asynchrony shortens the total time spent in the nest and explained 28% of the variation in nesting time from clutch completion to fledging. I present experimental evidence that brood reduction resulting from hatching asynchrony may be particularly adaptive towards the end of the breeding season, with 91% of the variation in the productivity of asynchronously-hatched broods being explained by, and increased with, date of hatching. About one fifth of birds delayed daytime incubation until after clutch completion, probably in wait for caterpillars to appear. Although the delay period was variable and extended total nesting time it always resulted in synchronous hatching. I propose that Blue Tits may have evolved plastic responses to environmental cues such as oak bud burst, which causes them to incubate at the optimum time to ensure maximum fledging success and chick fitness.
2

Egg size variation and breeding characteristics of the Black-winged Stilt Himantopus himantopus in a Saharan oasis

100%
Adamou A.-E., Kouidri M., Chabi Y., Skwarska J., Banbura J.
Acta Ornithologica
|
2009
|
tom 44
|
nr 1
Different aspects of the breeding biology of the Black-winged Shit were studied in a natural oasis wetland area in the Sahara Desert, the Chott of Aïn El Beïda, near Ouargla, E Algeria in 2004-2007. In this wetland the water level is independent of rainfall and Stilts start egg laying when average daily temperature increases to ca. 15°C, mostly in April-May, with no significant differences between years. Complete clutches usually consist of 4 eggs but 3 egg clutches happen with low frequency (2.9-5.6%). Egg size traits (mass, length, breadth and volume) tended to decrease from 2004 to 2007, probably due to deteriorating hydrological conditions of the wetland. Within-clutch variability showed both significant repeatability and laying-sequence-dependent differences among eggs, with the final egg being smaller than the clutch mean value. We found that all egg traits studied showed a negative correlation with the date of laying, which seems to be a phenomenon analogous to the seasonal decrease in clutch size, typical of birds with more variable clutch sizes. Hatching tended to be asynchronous, with average clutch hatching time being 1.84 days. The small final egg and hatching asynchrony are typical components of the adaptive brood reduction, the phenomenon not being recorded so far and remaining for future studies on the Black-winged Stilt. These are the first published data on breeding characteristics for any N African population of the Black-winged stilt.
3

Hatching asynchrony in the Red-breasted Flycatcher Ficedula parva in relation to breeding season, peak food abundance, and high predation

100%
Mitrus C.
Acta Ornithologica
|
2008
|
tom 43
|
nr 1
113-117
Hatching asynchrony has been recorded in many altricial bird species. Also, more than 70% of clutches of the Red-breasted Flycatcher hatched asynchronously. The annual variation in the proportion of asynchronous clutches depended on median dates of egg laying, in the years when females started egg laying later more asynchronous clutches were observed. The females from synchronous clutches started egg laying significantly earlier than females from asynchronous clutches and were more synchronised with the peak of caterpilars. No differences in clutch size and number of fledglings between asynchronous and synchronous clutches were found. The frequency of females that started incubation earlier showed no significant difference when mated with either after-2nd-year or 2nd-year males. Also, breeding success was not significantly different between broods of various hatching types and was 87% for asynchronous clutches and 94% for synchronous clutches. The time of breeding and high predation pressure could be main reasons for females of the Red-breasted Flycatcher to start incubation before laying the last egg of its clutch.
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