Accounting for the low survival of the Critically Endangered northern bald ibisGeronticus eremitaon a major migratory flyway

Abstract

The poor survival rate of immature northern bald ibises Geronticus eremita during their first years spent outside the natal site is driving the last known wild colony of the migratory eastern population to extinction. To inform emergency conservation action for this Critically Endangered species we investigated the distribution range and behaviour of immature birds in passage and wintering areas, and the threats to which they are subject. We integrated recent satellite telemetry data with visual observations spanning 130 years. We assessed threats across the range, using satellite tracking and field surveys. Our results show that during the years before they return to the natal site in Syria, immature northern bald ibises reside away from the recently identified adult wintering site in the central Ethiopian highlands. They occur mainly across the northernmost 70-80% of the adult migratory range. Historical records suggest that immature birds spend more time along the western Arabian Peninsula now than in the past. This range shift exposes them for longer periods to threats, such as hunting and electrocution on power lines, which are absent from the wintering site used by adult birds. We suggest that other threatened and declining bird species sharing the same flyway probably face the same threats during migration.

Back into the wild: establishing a migratory Northern bald ibis Geronticus eremita population in Europe

“…Former wintering sites are known along the African west coast down to Mauretania and Senegal, in Ethiopia and Eritrea, and at the southern end of the Arabian Peninsula (Bowden et al ., ; Serra et al ., ). Data on the regulation and patterns of migration for this species are mainly available from a now extinct migratory population observed in the Middle East (Serra et al ., ) and from our own release population, which comprises descendants from former colonies originating in the Moroccan Atlas (Böhm & Pegoraro, ). The birds have a genetic disposition to migrate, which includes pre‐migratory fattening (Bairlein et al ., ), along with increases in body weight and corticosterone levels (Fritz et al ., ).…”

“…This is particularly related to the quite unexpected discovery in 2002 of a relict population in Syria. The population comprised only seven individuals, which were still migrating along a historic migration route between Syria and Ethiopia (Serra et al ., ). Significant international efforts followed to preserve this relict population (Serra et al ., , ).…”

“…Under certain ecological conditions Northern bald ibis populations appear to change to a permanent sedentary lifestyle. This may have occurred particularly along coastlines with a year‐round temperate climate as is the case for the two remaining Moroccan populations or the release population in Andalusia (Serra et al ., ; Lopez & Quevedo, ). A similar situation has been recorded in other migratory species, such as White stork (Shephard et al ., ).…”

“…Northern bald ibis used to be a migratory species with a historic breeding range from the Middle East to Morocco (Kumerloeve, 1978;Bowden et al, 2008;. Former wintering sites are known along the African west coast down to Mauretania and Senegal, in Ethiopia and Eritrea, and at the southern end of the Arabian Peninsula (Bowden et al, 2008;Serra et al, 2015). Data on the regulation and patterns of migration for this species are mainly available from a now extinct migratory population observed in the Middle East and from our own release population, which comprises descendants from former colonies originating in the Moroccan Atlas (B€ ohm & Pegoraro, 2011).…”

“…In Europe, the birds reach a state of migratory readiness at the beginning of August. There are indications, from different release projects, that juvenile Northern bald ibis during their first autumn migration follow an internal vector that heads them south/ south-west Serra et al, 2015;Yeniyurt et al, 2016). However, as known from studies of White stork Ciconia ciconia and other species, juveniles depend on social information from more mature conspecifics to reach common wintering sites for the first time (Chernetsov et al, 2004;Flack et al, 2016).…”