Data from: Evolution of leap-frog migration: A test of alternative hypotheses

Leap-frog migration is a common migration pattern in birds where the
breeding and wintering latitudes between populations are in reversed
latitudinal sequence. Competition for wintering and breeding sites has
been suggested to be an ultimate factor and several competitor-based
hypotheses have been proposed to explain this pattern. If wintering sites
close to the breeding sites are favored, competitive exclusion could force
subdominant individuals to winter further away. Competitive exclusion
could be mediated either through body size or by prior occupancy. The
alternative “spring predictability” hypothesis assumes competition for
sufficiently close wintering areas, allowing the birds to use
autocorrelated weather cues to optimally time spring migration departure.
To test predictions and assumptions of these hypotheses, we combined
morphometrics, migration and weather data from four populations of common
ringed plover breeding along a latitudinal (56-68°N) and climatic gradient
(temperate to Arctic). Critical for our evaluation was that two
populations were breeding on the same latitude in subarctic Sweden and had
the same distance to the closest potential wintering site, but differ in
breeding phenology, and wintered in West Africa and Europe, respectively.
Thus, while breeding on the same latitude, their winter distribution
overlapped with that of an Arctic and temperate population, respectively.
Body size was largest within the temperate population, but there was no
size difference between the two subarctic. Populations wintering in Europe
arrived there before populations wintering in Africa. The largest
variation in arrival of meteorological spring occurred at the temperate
breeding site, while there was almost no difference among the other sites.
In general, temperatures at the northernmost wintering area correlated
well with each breeding site prior to breeding site-specific spring
arrival. Based on these observations, we conclude that competitive
exclusion through body-size related dominance cannot explain leap-frog
migration. Furthermore, the assumptions on which the ‘spring
predictability’ hypothesis is based did not match the observed wintering
ranges either. However, we could not reject the hypothesis that
competitive exclusion mediated by prior occupancy in the wintering area
could lead to leap-frog migration, and therefore this hypothesis should be
retained as working hypothesis for further work.