A record of breeding–moulting overlap in the Common Redstart Phoenicurus phoenicurus

Abstract

Capsule Moult-breeding overlap in a male Common Redstart feeding a second brood may reflect time pressure to fit moult between the completion of breeding and migration.

Post-nuptial moult and breeding are competitive life-history activities in most species of altricial birds. A change of feathers reduces flight capability which is essential for successful reproduction, especially in the period of feeding nestlings. In long-distance migrants with a complete moult after breeding (e.g. Common Redstart), the time available for moulting is limited by the start of the autumn migration. Nonetheless, migration is usually separated from the moulting period (although a partial moult of body feathers during migration is documented in some species, Herremans 1990). As a solution, a temporal overlap between breeding and moulting may occur, especially in species and populations breeding in the far north (Jenni & Winkler 1994). There may also be differences in the frequency and intensity of the overlap between males and females (e.g. Morton & Morton 1990, Siikamäki et al. 1994, Hemborg 1998). Breeding-moult overlap is rare in females, which tend to invest more in their current reproductive attempt. In males, the start of moult and the amount of parental care is more flexible and so breeding–moult overlap may be more common in some populations (Hemborg 1998).

Here we describe a case of early moulting in a breeding adult of Common Redstart Phoenicurus phoenicurus. As a part of a study of the ecology of this species, we check and ring breeding adults. The study population breeds in nestboxes in a pine Pinus forest at an altitude of 300 m, in east Bohemia, 50°10′N, 15°57′E, Czech Republic. About 65% of the population breeds twice during a season with a median hatching date of the second broods of 26 June (Porkert & Zajíc 2005). From 23 June to 2 July in 2010 and 2011 we caught seven males and seven females from nine nests during feeding (or incubation in one case) of their second broods. Five males and three females were one year old (i.e. hatched in the previous season, 2Y), the remaining six individuals were two years or older (+2Y). One male caught on 2 July was one year old (2Y) and had already started a post-nuptial moult (Figure 1a,b). The moulted feathers were symmetrical between both wings: primaries 1–2 (counted from the inner wing) had started to moult in a reverse from the ordinary order – primary 2 (about 40% grown, appearing from the sheath), primary 1 (about 30% grown, hidden in the sheath); primary coverts 1–2 appearing from the sheaths; carpal covert hidden in the sheath or starting to appear. A strip of about 10 orange feathers were in moult on the breast. The rest of the male's feathers were old: all remaining flight feathers and probably rectrices were juvenile; greater coverts 1–7 juvenile, 8–10 post-juvenile; alula 2–3 juvenile, 1 post-juvenile. The extent of post-juvenile feathers was typical and also the sequence of moulting was fairly normal for the species (Cramp 1988, Jenni & Winkler 1994, Ginn & Melville 2011). The described male in a pair with a female was feeding a brood which included three five-day-old chicks (hatched on 27 June) and two unfertilized eggs. The male may have started moulting several days previously but a more accurate date is uncertain due to a possible retarded moult during breeding (Flinks et al. 2008, Buchmann et al. 2009, see the last paragraph). The first breeding attempt of the male in the season was successful (started on 30 April) but the outcome of the second attempt is unknown (started on 10 June). The size of the male's broods corresponded to the brood sizes common in the population: first brood size = 6 eggs versus mean first brood size ± SD = 6.30 ± 0.88 eggs, second brood size = 5 eggs versus mean second brood size ± SD = 5.39 ± 0.94 eggs (Porkert & Zajíc 2005). The male's body weight was 13.50 g, at the lower end of the weight range of the males in the population (mean ± SD = 14.36 ± 0.73 g, n = 23). The male was paired with the same female in both first and second breeding attempts. None of the other birds in the study were found to be moulting (i.e. only 1 in 7 males and 0 in 7 females).

Figure 1. Moult of a male Common Redstart Phoenicurus phoenicurus while feeding a second brood of five-day-old chicks, Czech Republic, 2 July 2010: (a) right wing, moulting primaries 1–2, primary coverts 1–2, carpal covert; (b) lower part of a body, moulting breast feathers.

The moult in the European population of Common Redstart usually starts in the first half of July and lasts for 40–50 days until August (Snow 1969, Menzel 1984, Cramp 1988, Glutz et al. 1988, Ginn & Melville 2011). There are several records of very early moult from the first half of June but these were probably non-breeding individuals (Menzel 1984). Brood care may affect the timing of moult as the birds with only a single brood moult earlier than birds breeding twice a season (Dementiev & Gladkov 1954). An overlap between breeding and moulting occurs occasionally (Jenni & Winkler 1994) but probably in late broods only. In a population of Common Redstarts studied in the west of Germany, Winkel (1986) found no overlap in males breeding in June but five out of six breeding males were found to be moulting in July. Of these, the most advanced male moulted primaries 1–4 and tertial 2 while feeding five-day-old chicks on 16 July in what was probably an extremely late breeding attempt. However, our observed case documents an early moult well within the normal period for second broods rather than an overlap coincident with late breeding.

There are three possible strategies for adult birds to manage complete moult in a limited time interval after a prolonged reproductive period.

1.	Extension of the moult into the migration period. A complete change of remiges are necessary, however, for efficient flight especially in long-distance migration (Ginn & Melville 2011). Despite this, late breeding female Northern Wheatears Oenanthe oenanthe probably start autumn migration with growing outer primaries (Buchmann et al. 2009).
2.	Speeding up the moult and thus shortening the moulting period. However, the speed of feather growth seems to be limited and an increase in the number of feathers grown simultaneously may reduce their quality. In studies of experimentally shortened moult period, rapidly moulting birds had lower total feather mass, which resulted in feathers which were poorer for insulation and decreased the survival and fitness of the individuals (Nilsson & Svennson 1996, Dawson 2004).
3.	Overlap of moult with the breeding period. Although this strategy is more commonly used, it is also constrained. The total energy available for a parent is limited and any energy diverted to self-maintenance (including moult) will mean less energy is available for the current brood. It seems likely that the intensity of moulting may therefore be lower during any overlap period, and this changes to a higher constant speed after the young become independent (e.g. see Flinks et al. 2008, Buchmann et al. 2009). The extension of moult into a reproductive period may be also complicated by intersexual conflict. One parent may desert the nest or lower its investment in the care of the young to start its moult and thus increase the current cost of the brood to its breeding partner (Morton & Morton 1990). In our observation involving the male Common Redstart we have neither information of the speed of a moult nor any data of the male's real share of chick feeding. If the male continued feeding its chicks it is possible that the breeding–moult overlap would have continued for a further 16 or more days.

Acknowledgements

We thank the editor and both reviewers for their expert and valuable comments to the manuscript.