Spatial patterns of white stork (Ciconia ciconia) migratory phenology in the Iberian Peninsula

Abstract

In contrast to the attention attracted by temporal trends of phenology, the spatial patterns of arrivals, departures or stays of trans-Saharan birds are still nowadays largely unknown in most of their European breeding areas. In the case of the white stork (Ciconia ciconia), some studies have attempted to describe its migratory patterns throughout some European countries but, to our knowledge, no one has related these patterns to some kind of explanatory variable which offers an ecologically-based explanation for the heterogeneous phenology observable among populations. Here, arrivals, departures and stays of this species, recorded in hundreds of Spanish localities, were related to a set of environmental, geographical, biological and spatial predictors, and modeled by multiple regression. The best model for arrival dates accounted for up to 34% of variability of data and pointed towards an earlier arrival in those populations located in south-western Iberia and with higher population densities. This last relationship is probably due to the competition for nest-site fidelity maintenance. However, no variable was able to explain properly the blurred spatial pattern recorded for departure dates. Departure decisions are strongly influenced by social behavior in this species and depend on collective decisions influenced by peculiar local environmental conditions of each year rather than macrogeographical gradients. Environmental, geographical or spatial variables also did not capture much of the observed variability in the length of the stays among populations. However, this variable was strongly related to the arrival and departure dates of populations. White storks stay longer in localities with earlier arrivals and, especially, later departures.

Census methods for White stork (Ciconia ciconia): bias in sampling effort related to the frequency and date of nest visits

“…In fact, breeders are not totally attached to their nest until egg laying. In addition, some pairs have not yet arrived in the breeding zone in February, March, and even April (Prieto 2002;Gordo et al 2007;Vergara et al 2007a). However, later in the breeding season, when chicks are 23 days old, they are able to thermoregulate (Tortosa and Castro 2003), and consequently parents may leave them alone in the nest while they are foraging (Tortosa and Villafuerte 1999).…”

“…We selected these six colonies to obtain a representative range of breeding dates in Spain because this species shows a great variation in the arrival dates among zones (Gordo et al 2007). In order to avoid disturbance of breeding birds and bias on data, a few nests randomly selected within each colony were controlled from the same point away from the colony during a fixed time (2 h) in each survey.…”

The relative importance of conditions in wintering and passage areas on spring arrival dates: the case of long-distance Iberian migrants

“…In fact, populations from SW Spain are notably earlier than those from the rest of the country (see mean arrivals in Table 1). The geographical patterns of the arrival dates of the White Stork were not clear (Gordo et al 2007b) and did not allow an easy and objective division of Spain into an early and late region, respectively. For the Nightingale, the distribution of arrival dates was narrow (see low standard deviation in Table 1), i.e.…”

Timing of arrival at breeding grounds determines spatial patterns of productivity within the population of white stork (Ciconia ciconia)

“…Under such conditions, a density dependence in reproductive success is likely to occur, which has already been reported for different European populations of white stork (Barbraud et al 1999;Sasvári et al 1999). It has also been demonstrated that storks from areas of high breeding densities arrive earlier in spring, indicating that intense competition takes place for attractive nesting territories (Gordo et al 2007). Finally, there is strong empirical evidence for the fitness benefits associated with early arrival of storks (Tryjanowski et al 2004; but see Janiszewski et al 2013), which suggests that delayed arrival may coincide with less favourable environmental conditions and, possibly, with lower food availability.…”