|| 要旨トップ | 目次 |
|日本生態学会第60回全国大会 (2013年3月，静岡) 講演要旨
一般講演（ポスター発表） P1-249 (Poster presentation)
Philopatry is an optimal strategy for securing reproduction at the promising natal places. It is observed at the population level as well as the individual level. Such collective philopatry is well known in seabirds breeding colonies, but actual rate of philopatry cannot be quantified because this philopatry is caused by the limitation of breeding sites. On the other hand, herons and egrets form annual breeding colonies on abundant resources such as trees or bamboo thickets. Here we examined the rate of philopatry of heron colonies around Ibaraki Prefecture where 143 colony sites were recorded in the last half century. We categorized them into 54 lineages by clustering those that were consecutively established within 6 km radius. Twenty out of 54 lineages (44%) showed perfect philopatry using exactly the same site consecutively for more than a year. Sixteen out of 54 lineages moved colony sites more than once. We estimated focal points of attraction for those 16 lineages and calculated deviations between those points from the centroids of lineage trajectories. Distances between centroids and focal points for randomized lineage trajectories were significantly larger than the real lineage trajectories. We concluded that even moving colonies were philopatric and insisted on remaining the same colony sites.