Low asymmetry of primary moult in Dunlins Calidris alpina alpina migrating to wintering grounds

Abstract

The Dunlin is one of very few wader species that moults primaries when migrating to its wintering grounds. In our study, a total of 68.2% of immatures and 26.6% of adults underwent their primary moult when passing through the southern Baltic in autumn. More than 30% of moulting birds revealed differences in moult scores of left and right wings. However, 13% of Dunlins showed differences between the left and right wing not greater than 1%, and 50% of individuals showed differences between the two wings that were lower than 3% of the total mass of all primaries. The probability of asymmetry during the primary moult increased over time and decreased with the advancement of the primary moult. Sex and age of birds had no significant effect on the occurrence of moult asymmetry. The level of asymmetry in the primary moult increased in the following days of autumn migration and with the advancement of the primary moult. The mean index of primary moult asymmetry (the absolute value of the difference in moult advancement between the left and right wing) was lower in immature Dunlins than in adults, and in females compared to males. Hence, sex (males) and age classes (adults) that spend a longer time on the breeding grounds revealed a higher index of primary moult asymmetry, most probably as a result of higher levels of physiological stress. However, the low proportion of birds showing large asymmetry suggests that this is strongly constrained by selection for aerodynamic efficiency, as asymmetry in primaries affects aerodynamic stability, takeoff costs, manoeuvrability and agility in birds with flapping flight.

Body Condition of the Upland Sandpiper (Bartramia Longicauda) en Route Through Central Mexico

“…Feather FA values on our sample (wing 1.1%, rectrix 4.3%) are low compared to other shorebirds, which can reach in certain individuals over 20% (e.g., Meissner et al 2019), showing no signs of flight-related (aerodynamics) stress. There are no data on FA for Upland Sandpipers elsewhere.…”

“…Differences in body weight between birds from our sample and studies from southern latitudes seem to reflect weight loss through stored lipid depletion as fuel during long flights (Jenni-Eiermann et al 2002). Asymmetry values are usually lower in primaries of migratory birds (Meissner et al 2019), which have more symmetrical wings than more sedentary species (Balmford et al 1993). Food scarcity seems to affect feather keratin synthesis and therefore levels of asymmetry in feathers (Swaddle and Witter 1994, Møller 1996, Freed & Cann 2012.…”

“…Food scarcity seems to affect feather keratin synthesis and therefore levels of asymmetry in feathers (Swaddle and Witter 1994, Møller 1996, Freed & Cann 2012. High levels of asymmetry can show poor body condition or nutritional stress during molt (Meissner et al 2019), as feather length and asymmetry are determined during molt. We found that asymmetry levels in our study showed a negative relationship with fat scores, which suggests that individuals with higher scores during migration were probably less stressed and in better condition during molt, leading to lower levels of asymmetry.…”

“…Information on fluctuating asymmetry (FA) is also lacking for the species. FA reflects an animal's ability to cope with the sum of challenges that affect it during the growth period and can signal physical responses of individuals to environmental stress, as it results from physiological stress (Møller & Pomiankowski 1993, Meissner et al 2019. If available, such data as morphometric measurements, body condition, and FA can be interpreted to better describe the life stages of the species during migration and used to construct tools for future management (see Cimprich & Moore 2006, Morrison et al 2007.…”