Body mass and geographic distribution determined the evolution of the wing flight-feather molt strategy in the Neornithes lineage

2022

Ibis

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An understanding of feather moult, an important process in the life cycle of birds, lags behind that of other avian life-history events. This lag includes a lack of scientific attention, but surprisingly also a lack of basic knowledge regarding the moult strategy of many bird species. This situation is particularly astonishing in light of the fact that feathers are a unique characteristic of birds. Currently, there are two main terminology systems for describing moult: one life-cycle-based and one plumage-based (H-P terminology). A survey conducted among 434 birdwatchers, bird-ringers (banders) and ornithologists showed a significant difference in understanding of the two terminologies. Ornithologists studying moult, as well as editors and reviewers, are called upon to make use of, and encourage the use of, understandable moult terminology, as much as possible. Using more understandable terms and language may help a wider audience of amateurs, students and ornithologists to understand moult. Involvement of a wider audience may advance data collection and research of this important event in the avian life cycle.

“…2009, Kiat & Izhaki 2016a, Kiat et al . 2021) and plumage coloration (Delhey et al . 2020, Kiat & Sapir 2022).…”

Section: Figureunclassified

“…For example, moult is affected by a bird's geographical distribution (Kiat et al . 2020b, 2021), including the distribution changes that occur throughout the annual cycle as a result of migration (Barta et al . 2008, Kiat et al .…”

Section: Figurementioning

confidence: 99%

Moult terminology: Let's make it simpler!

2022

Ibis

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“…(2022) and concluded that replacing new feathers by juvenile birds is an optimal strategy in favourable habitats and under low time constraints (see also Kiat et al . 2021).…”

Section: Figurementioning

confidence: 99%

“…In fact, complete moult of flight feathers, which includes renewal of all six secondary feathers, by juvenile birds a few months after their growth is a common pattern which has evolved mainly among smaller‐bodied species or those that moult in equatorial regions (Kiat et al . 2021). Here, we tested 275 Western Palaearctic passerine species and found that 49.8% moult at least part of their secondaries during the first year of their life (17.1% of species moult part of secondaries and 32.7% moult all six secondaries; Fig.…”

Section: Figurementioning

confidence: 99%

Split moult: a response to time constraints during the main moult period

Izhaki

2022

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Split moult is a relatively rare adaptation to cope with time constraints in the annual cycle, although less rare than previously thought. This moult pattern mainly occurs among long‐distance migrants but also among some northern species wintering in the northern or temperate zones. Hedenström et al. rejected the conclusion of Kiat and Izhaki that split moult is a time constraint strategy; instead, they advocated the view that it is an endogenously controlled strategy. They based their conclusion on the first winter secondaries moult by juvenile birds and on the post‐breeding moult sequence. In contrast, we argue that Hedenström et al.'s conclusions are flawed, probably due to their focus on only one species (Barred Warbler Curruca nisoria). Our results suggest that there are no indications of the uniqueness of the secondaries moult by juvenile birds in relation to other species which have no split moult. We thus suggest that split moult is not initiated during the birds' first winter. In addition, there is no difference in moult sequence, although decoupling between two feather tracts occurs (primaries and secondaries), which is a common mechanism among many passerines that perform a partial or incomplete moult. We therefore argue that split moult is an adaptive strategy driven largely by the actual time constraints the birds experience, as already experimentally proven.

“…Avoiding a complete moult or splitting the annual moult into two separate moults mostly occurs under time constraints during the annual cycle or when birds are faced with temporary resource limitation (Kiat et al 2019a, Jenni & Winkler 2020a, Kiat & Izhaki 2021. These constraints may result from environmental conditions, for example a short period of resource abundance (Kiat et al 2020b), or as a result of morphology and life-history trait-related constraints, such as large body size and high flight dependence resulting in a longer moult , Kiat et al 2021b). Long moult duration might be a result of shedding and subsequently regrowing fewer flight feathers in parallel, a strategy that reduces potential aerodynamic impairments (Rohwer et al 2009 or also due to slow feather growth rate (Rohwer et al 2009, Jenni & Winkler 2020a.…”

mentioning

confidence: 99%

The relationship of moult timing, duration and sequence to the aerial lifestyle of the Little Swift (Apus affinis)

Bloch

2023

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Feather moult is an important and energy‐demanding avian life‐history trait that is necessary to maintain the function of the plumage by replacing abraded feathers with new ones. However, during moult, aerodynamic capacity is temporarily impaired by the reduction and shape change of the flight surface. Therefore, among aerial birds, adaptations may evolve to reduce this impairment. Here, we studied the timing, duration and sequence of the annual complete moult of adult Little Swifts Apus affinis in northern Israel by examining the plumage of 55 individuals monthly in their colony. Primary moult occurs over 191.7 ± 24.0 days, representing 52.5 ± 6.6% of the annual cycle, and overlaps with the breeding season, a rare occurrence among small Palaearctic bird species. In addition, primary moult duration was significantly affected by its timing such that individuals that started to moult later had a shorter moult duration than those that started to moult earlier. This relationship is most likely to be a result of the time available for moult, which is limited by breeding and also by the cold season and the expected decline in food availability. Moult overlap with breeding or cold seasons may involve energetic and functional costs. Our results indicate two strategies that appear sequentially: (1) a slow and long moult that largely overlaps with breeding, and (2) a shorter moult that overlaps less with breeding (both strategies avoid moulting during the cold season). Most Little Swifts (85.7%) moulted their rectrices in a centripetal sequence starting with the outermost pair of rectrices inward. This moult was later in relation to wing feather renewal and had almost no overlap with primary moult. Finally, we tested a method for non‐invasively monitoring moult of small species by collecting and sampling shed feathers without the need to capture the birds themselves, as has been successfully used for larger bird species. This work demonstrates the importance of aerodynamic considerations in the evolution of life‐history traits. Moult‐related aerodynamic costs may be an important evolutionary factor shaping moult strategy, including timing, duration and sequence, mainly among species, like swifts, that are highly dependent on their aerodynamic ability.