Moult Strategies Affect Age Differences in Autumn Migration Timing in East Mediterranean Migratory Passerines

Abstract

Adult passerines renew their flight feathers at least once every year. This complete moult occurs either in the breeding areas, just after breeding (summer moult), or, in some long-distance migratory species, at the non-breeding areas, after arrival to the southern wintering area at the end of autumn migration (winter moult). The aim of this study was to relate moult strategies with the DMD, the difference in median migration date, through Israel, between juveniles and adults. Our data on autumn migration timing in juveniles and adults was based on ringing data of 49,125 individuals belonging to 23 passerine species that breed in Europe and Western Asia and migrate through Israel. We found that DMD was associated with moult timing. In all species that perform a winter moult, adults preceded juveniles during autumn. Among migrants who perform a summer moult, we found evidence of both migration timing patterns: juveniles preceding adults or adults preceding juveniles. In addition, in summer moulters, we found a significant, positive correlation between mean breeding latitude and DMD. Although previous studies described that moult duration and extent can be affected by migration, we suggest that moult strategies affect both migration timing and migration strategy. These two moult strategies (summer or winter moult) also represent two unique migration strategies. Our findings highlight the evolutionary interplay between moult and migration strategies.

Fig 1. The ringing sites: (1) Jerusalem Bird Observatory 31°46'N / 35°12'E, (2) Modiin Hills 31°52'N / 34°59'E, (3) Einot-Gibton Nature Reserve 31°51'N / 34°52'E, (4) Tel-Ekron 31°46'N / 34°51'E, (5) Soreq Valley 31°46'N / 34°55'E, (6) Ella Valley 31°41'N / 34°58'E, (7) Beit-Qama Fields 31°26'N / 34°45'E, (8) Ein-Rimon 31°22'N / 34°50'E and (9) Be'er-Sheva Valley 31°15'N / 34°46'E.

Fig 2. Phylogenetic tree for the 23 species included in analysis based on BirdTree.org [31].

Fig 3. The difference in median migration date (DMD), through Israel, between juveniles and adults (days) in winter moulters (n = 8 species) and summer moulters (n = 15 species).

The difference between the two groups was significant) Mann-Whitney U-Test, U = 3.00, Z = 3.69, P < 0.001).

Fig 4. The difference in median migration date (DMD), through Israel, between juveniles and adults (days) in relation to breeding latitude and moult strategy, summer (A) or winter (B), in 23 passerines species.

The difference between slopes is significant (P < 0.05); dashed curves represent 95% regression confidence intervals.