The northern bald ibis Geronticus eremita is one of the few Critically Endangered bird species whose breeding range is confined to the Western Palearctic. At present two disjunct natural populations are known: in Morocco, and in Turkey and Syria. In Morocco the population consisted of c. 116 breeding pairs in 2015. In the Middle East the population has suffered a long-term decline; in Turkey there is a semi-captive colony, and in Syria a small colony was discovered in 2002 (Serra et al., 2004, Oryx, 38, 106–108), with birds migrating to Ethiopia (Lindsell et al., 2009, Oryx, 43, 329–335). In Europe the species became extinct c. 400 years ago, although it was previously widely distributed. European birds were known to leave their breeding areas in autumn and to return in spring, although the location of their historical wintering areas is unknown. Could the species' movements be similar to those today of the glossy ibis Plegadis falcinellus and the spoonbill Platalea leucorodia, involving the crossing of the Strait of Gibraltar?
Reintroducing threatened species is an eye-catching approach to saving species maintained in captivity. This has recently been the case for the northern bald ibis in southern Spain, where 257 birds were released during 2004–2011 in the context of a project evaluating the efficacy of different controlled release methods (López et al., 2015, Quercus, 349, 15–23). In 2008 reproduction in the reintroduced population was confirmed for the first time, and since then the ibises have bred every spring, with a slow increase in numbers.
Here we report the first confirmed sighting of northern bald ibises successfully reaching Morocco after crossing the Strait of Gibraltar, a matter that could have important implications for conservation of this species in an intercontinental area. On 2 November 2016, whilst monitoring migration of the griffon vulture Gyps fulvus, we observed a group of six northern bald ibises reaching the Moroccan coast from Europe. They were first detected at a great distance while flying southwards over the sea, and reached the Moroccan coast at the same point where the arrival of soaring birds was taking place.
Since January 2008 we have regularly visited the wetlands of northern Morocco to survey birds and we have never seen the northern bald ibis there, nor have we received reports of the species. The Moroccan breeding colonies of the northern bald ibis are c. 700 km south of our observation point.
To our knowledge this is the first observation of a group of northern bald ibises successfully reaching Morocco after crossing from Spain. The only other observation was of a single Spanish-ringed northern bald ibis on 24 May 2007 (Plate 1), in Merja Bargha (116 km south-west of our observation location, in a coastal wetland; Teo Todorov, pers. comm.). These observations suggest that the reintroduced ibises are expanding their home range southwards, which could indicate a progressive adaption of the population.
With the Spanish population increasing, the crossing of the Strait of Gibraltar, in both directions, will probably become more regular, and could have far-reaching consequences for both the Moroccan wild population and for the reintroduction programme in Spain. Many questions require investigation: Will these ibises return to Spain? Where are their staging areas in Morocco? Is Morocco acting as a sink for the Spanish population? Could these dispersal movements be the start of new breeding colonies in northern Morocco? Most importantly, could these birds contact the unique and isolated wild colonies in southern Morocco and interbreed with them? Considering the precarious conservation status of the northern bald ibis, and the severe environmental impacts northern Morocco is suffering, it is time to commence cross-border collaboration and conservation action for this Critically Endangered species.