Differences in tail feather growth rate in storm-petrels breeding in the Northern and Southern hemisphere: a ptilochronological approach

Abstract

Moulting and breeding are costly stages in the avian annual cycle and may impose trade-offs in energy allocation between both stages or in their timing. Here, we compared feather growth rates (FGR) of rectrices in adults between two pairs of small pelagic Procellariiformes species differing in moult-breeding strategies: the European storm-petrel Hydrobates pelagicus and Leach’s storm-petrel Oceanodroma leucorhoa breeding in the Northern Hemisphere (Faroe Islands), showing moult-breeding overlap in tail feathers; and the Wilson’s storm-petrel Oceanites oceanicus and black-bellied storm-petrel Fregetta tropica, breeding in the Southern Hemisphere (South Shetlands), temporally separating moult and breeding. We used ptilochronology (i.e., feather growth bar width) to reconstruct FGR reflecting relative energy availability during moult. Based on previous research, we expected positive correlations between feather length (FL) and FGR. Additionally, we expected to find differences in FGR relative to FL between the moult-breeding strategies, where a relatively higher FGR to FL indicates a higher energy availability for moult. To investigate if energy availability during moult in the studied species is similar to species from other avian orders, we used FGR and FL found in literature (n = 164) and this study. We fitted a phylogenetic generalized least squares (PGLS) model to FGR with FL, group (i.e., Procellariiformes vs. non-Procellariiformes) and the interaction FL * group as predictors. As it has been suggested that Procellariiformes may form two growth bars per 24 h, we fitted the same model but with doubled FGR for Procellariiformes (PGLSadj). The group term was significant in the PGLS model, but was not in the PGLSadj model, confirming this suggestion. Individually predicted FGR by the PGLSadj model based on FL, showed that the Southern species have a significantly higher FGR relative to FL compared to the Northern species. Additionally, we found no correlation between FL and FGR in the Northern species, and a positive correlation between FL and FGR in the Southern species, suggesting differences in the trade-off between feather growth and size between species from both hemispheres. The observed differences between the Northern and Southern species may be caused by different moult-breeding strategies. The Southern species may have had more energy available for moult as they are free from breeding duties during moult, while the Northern species may have had less free energy due to a trade-off in energy allocation between breeding and moulting. Our study shows how different moult-breeding strategies may affect relative nutritional condition or energy allocation during moult of migratory pelagic seabirds.

Birds of a feather moult together: Differences in moulting distribution of four species of storm-petrels

“…Additionally, while rectrix feathers are often moulted simultaneously with other flight feathers [ 14 , 24 ], storm-petrels also limit the number of feathers moulted at once [ 13 ]. Therefore, while the feathers sampled for our study have grown over a period of several weeks [ 59 ], they only represent part of the moulting period.…”

“…We determined the feather growth rate for the outermost rectrix by measuring growth bar width to the nearest 0.1 mm × d -1 . Feather growth bars are visible as alternating light and dark bands, formed during feather synthesis, but see Ausems et al 2019 [ 59 ] for a detailed description of the method used.…”

“…It took several weeks for the sampled rectrices to be fully grown (ESP 30.6 ± 8.5 d; LSP 40.8 ± 13.0 d; BBSP 18.5 ± 2.5 d; WSP 18.7 ± 3.0 d; [ 59 ]). Thus, the rectrix formation period, overlapping to a considerable extent with flight feather moult [ 14 , 24 ], includes a considerable part of the non-breeding period, even if feather growth started at the end of the breeding season.…”

Colony attendance and moult pattern of Cory's Shearwaters (Calonectris borealis) differing in breeding status and age

“…Moreover, Procellariiforms also have notably extended breeding periods and low development rates in pre-and post-embryonic phases, making them good models to study energy allocation decisions. Several species start to moult body, wing or tail feathers by the end of their breeding period whereas others partially overlap these activities (Hydrobates pelagicus Arroyo et al 2004 Ausems et al 2019). Furthermore, the ability of birds to modify their strategy depending on circumstances, as well as to suspend moult (Alonso et al 2009, Ramos et al 2009, allows species living in different environments and differing in size to migrate without the need to allocate nutrients to feather synthesis while maintaining high flight performance (Swaddle & Witter 1997, Hedenstr€ om & Sunada 1999.…”

“…2013, H. pelagicus and Oceanodroma leucorhoa Ausems et al . 2019). Furthermore, the ability of birds to modify their strategy depending on circumstances, as well as to suspend moult (Alonso et al .…”