Shortening day length as a previously unrecognized selective pressure for early breeding in a bird with long parental care

Abstract

Several different selective pressures have been suggested to explain an intense competition for early return to breeding grounds in birds. In this study we hypothesized that shortening day length during summer months may constitute additional selective force acting towards early breeding in avian species with long parental care. To test this hypothesis, we studied time budget and foraging activities of early-nesting and late-nesting white storks Ciconia ciconia from the Central-European population. We found that duration and distance of foraging trips increased significantly over the course of the reproductive season. The relative frequency of foraging trips increased at the expense of other activities, such as resting, plumage maintenance, and nest maintenance. Mean daily foraging duration increased with increasing day length in the early part of the season, with 0.68 h of foraging per individual per 13.16 h of day length in mid-April increasing to 7.42 h of foraging per individual during solstice (16.61 h of day length). Afterwards, mean foraging duration continued increasing in spite of decreasing day length, reaching 11.63 h of foraging per individual per 14.92 h of day length at the end of the season in mid-August, when storks were forced to continue foraging after sunset in order to meet energy requirements of fledglings. The results suggest that shortening day length during summer months may constitute a serious time constraint on food delivery rates to offspring for late-breeding pairs of white stork.Keywords Ciconia ciconia Á Foraging Á Photoperiod Á Timing of breeding Á White stork Zusammenfassung Kü rzere Tage sind ein bisher unbekannter Selektionsdruck fü r frü hen Brutbeginn in einer Vogelart mit langer elterlicher Fü rsorge Verschiedene Selektionsfaktoren wurden bisher herangezogen zu erklären, warum Vögel so intensiv konkurrieren möglichst früh im Brutgebiet anzukommen. In dieser Studie untersuchten wir die Hypothese, dass kürzere Tage während der Sommermonate in Arten mit langer Elternfürsorge einen weiteren Selektionsfaktor darstellen, der frühen Brutbeginn begünstigt. Um diese Hypothese zu testen verglichen wir die Zeiteinteilung und Dauer der Nahrungssuche bei früh und spät nistenden Weißstörchen Ciconia ciconia in einer zentraleuropäischen Population. Die Dauer und Entfernung von Nahrungsflügen nahm im Laufe der Brutsaison signifikant zu. Die relative Häufigkeit von Nahrungsflügen stieg ebenfalls an, was auf Kosten anderer Aktivitäten wie Rast, Gefiederpflege und Nestpflege geschah.

Smart nest box: a tool and methodology for monitoring of cavity‐dwelling animals

“…Parental care intensity may vary during the breeding season (Podlaszczuk et al . ), with increasing nestling age (Liu et al . ), changing food supply (Zárybnická, Sedláček & Korpimäki ), ambient temperature (Conway & Martin ) or day length variation (Shaw & Cresswell ).…”

Extra-pair paternity in the socially monogamous white stork (Ciconia ciconia) is fairly common and independent of local density

“…Fledging occurs between 58 and 64 days after hatching30, and after first breeding at age 2–4 years, adults attempt to reproduce annually31. Because the white stork is large, identifiable, and easily observed during breeding, due to a preference to nest in open areas near human settlements, this species is a common subject for scientific studies on reproduction (e.g 343536373839…”

“…Because the white stork is large, identifiable, and easily observed during breeding, due to a preference to nest in open areas near human settlements, this species is a common subject for scientific studies on reproduction (e.g. 34 35 36 37 38 39 ).…”