Is There a “Migratory Syndrome” Common to All Migrant Birds?

Abstract

: Bird migration has been assumed, mostly implicitly, to represent a distinct class of animal behavior, with deep and strong homologies in the various phenotypic expressions of migratory behavior between different taxa. Here the evidence for the existence of what could be called a “migratory syndrome,” a tightly integrated, old group of adaptive traits that enables birds to commit themselves to highly organized seasonal migrations, is assessed. A list of problems faced by migratory birds is listed first and the traits that migratory birds have evolved to deal with these problems are discussed. The usefulness of comparative approaches to investigate which traits are unique to migrants is then discussed. A provisional conclusion that, perhaps apart from a capacity for night‐time compass orientation, there is little evidence for deeply rooted coadapted trait complexes that could make up such a migratory syndrome, is suggested. Detailed analyses of the genetic and physiological architecture of potential adaptations to migration, combined with a comparative approach to further identify the phylogenetic levels at which different adaptive traits for migration have evolved, are recommended.

Adaptations to migration in birds: behavioural strategies, morphology and scaling effects

“…This could be an insurance adaptation in migrants to get away from deteriorating ecological conditions in time, but it also shows that residents are 'pre-adapted' to develop migration or, alternatively, that they have evolved from migrants and retain certain characteristics from their migratory past. Be that as it may, the presence of migratory feats also in residents casts doubts on whether there are migration syndromes unique to migrants (Piersma et al 2005). Perhaps migration is the original characteristic of all birds and the differences we see between migrants and residents are only the loss of some adaptations among residents when not needed any longer.…”

“…The suite of modified characters that makes migrants better adapted for migration than resident species is often refereed to as the migration syndrome (e.g. Dingle 1996;Piersma et al 2005). The migration syndrome includes evolutionary modifications of morphology, the acquisition of orientation and navigation skills and behavioural adjustments in relation to ecological and external factors.…”

“…The migration syndrome includes evolutionary modifications of morphology, the acquisition of orientation and navigation skills and behavioural adjustments in relation to ecological and external factors. We may look at the migration syndrome from an engineering reductionist's viewpoint (Piersma et al 2005), while the bird solves all its problems at once and with apparent ease. Some of the feats we consider as 'adaptations' may not be that, but rather exaptations if they originally evolved for another function than their current one (Gould & Vrba 1982).…”

Organization of vertebrate annual cycles: implications for control mechanisms

“…The fact that some traits such as fat deposition, orientation, territoriality and many others may be expressed in different lifehistory stages poses the interesting question of whether they are regulated by different mechanisms. Piersma et al (2005) point out some examples where this may be the case when comparing migration traits with other life-history stages.…”

“…Again, the progression of life-history stages is analogous to the switching of phenotypes at the population level, only the 'switch' occurs within an individual. Piersma et al (2005) argue that such definitions for migratory syndromes might not be very clear because many traits are controlled differently across species, or because migrants express several traits (e.g. orientation, fat deposition) in other life-history stages.…”