Eurasian Spoonbill chicks receive parental care up to several months after fledging, but not into migration

Abstract

Despite its potential role in affecting survival, habitat use and migration strategies of juvenile birds, post-fledging parental care is poorly studied, as it requires that families can be followed over large distances. Here we combine visual observations of colour-ringed chicks being fed after fledging with GPS-tracking and accelerometer-based behavioural classification of fledged chicks and their parent(s) to quantify post-fledging parental care in Eurasian spoonbills in relation to age of the chick and sex of the chick or parent. We show that the number of observed feedings and the amount of overall contact between chicks and parents, i.e. when chick and parent were <10 m apart, strongly decreased with chick age. Chicks were observed being fed until 125 d old, always within 40 km of the natal colony. The amount of contact strongly varied among the 16 GPS-tagged chick-parent pairs, on average decreasing from 8% of contact time at 40 d old to <2% at 90 d. The last contact occurred at chick ages of 44-136 d (median: 88 d). All contact occurred within 18 km of the natal colony except for the first outbound migratory flight of one chick-parent pair. Both mothers and fathers engaged in post-fledging care, with some evidence that mothers had slightly more contact with chicks than fathers, overall as well as while the chick was begging or foraging. In 10 out of 11 cases that both chick and parent embarked on autumn migration, they did not migrate together: post-fledging care ended on average one week before the adults departure and four weeks before the chicks departure on autumn migration. Significance statementProlonged parental care may have positive effects on the survival and influence the habitat use and migration strategies of juvenile birds, as parents may continue to feed their young, show them suitable sites for foraging or resting or suitable routes for migration. Nonetheless, the duration of post-fledging parental care is poorly studied as it requires that parents and their young can be followed over large distances. Based on feeding observations and GPS-tracking of fledged chicks and their parent(s), we show that in Eurasian spoonbills Platalea leucorodia, the duration of post-fledging parental care is highly variable but ends before the onset of migration. This has important implications for the development of migration routines of juvenile spoonbills.