Northern bald ibis 939


in 2009; fledged young failed to reach the wintering site in Ethiopia, reappearing in only very low numbers in subse- quent years (Serra et al., 2014). Unsustainably high annual mortality (c. 85%) of young


birds outside the breeding grounds was the main reason for juveniles failing to return. Combined with breeding fail- ures in 2009 and 2010 resulting from unknown causes, this reduced the colony to one pair and an unpaired female by 2010. There was an attempted supplementation using Turkish birds in 2010, when two tagged juveniles were re- leased, with both successfully migrating to southern Saudi Arabia and surviving 6–8 weeks before dying (Bowden et al., 2012). In summer 2012, during the Syrian civil war, only one pair returned to the site but did not breed. Three adults had been observed in 2013–2014 at their wintering grounds in Ethiopia, and one in 2015, but only one of these birds returned to the breeding grounds in 2014; no free-flying birds were seen by late February 2015 (Mahmud Abdallah & Yilma Dellelegn, pers. comm., 2016). The Syrian population now appears to be functionally extinct, although since 2015 monitoring at the site has been extremely difficult because of security issues (Table 4).


Captive populations


The northern bald ibis has been kept in zoos since the 1930s. The first few birds were imported from the eastern popula- tion, but none survived for longer than a few weeks, probably because of poor husbandry. The first surviving northern bald ibises were juveniles imported from Morocco to Basel Zoo in the early 1950s. They became founders of the captive northern bald ibis population (Böhm, 1999), and now all northern bald ibises in European zoos derive from the western population. Overall there were 72 successful imports up to 1960, and a


further two during 1960–1970. Approximately 30 birds were imported in 1976 and 1978 to Zoo Rheine and Zoo Rabat. All captive birds can be separated into three bloodlines, termed Basel stock, Rheine stock and Rabat stock. All three lines have been mixed in most collections, and currently most zoos keep descendants of at least two bloodlines (Böhm, 2006). The captive population increased over 22 years from 330


in 1988 to . 1,100 birds by 2010, and 1,700 registered in the studbook by 2018. This increase is a result of breeding suc- cess (c. 100–130 offspring per year), low mortality and the longevity of the species. Since 1997 juveniles have been donated from European Endangered Species Programme sources to three research projects. The Konrad Lorenz Research Station, Austria, re- ceived 61 northern bald ibises from seven locations dur- ing 1997–2017 to establish a sedentary semi-captive colony (Table 5), 51 of which subsequently died. Since then, the


colony recovered sufficiently to require exchanges only with another nearby sedentary semi-captive colony in Tierpark Rosegg. The latter was set up with 25 birds in 2004–2011 (Table 5). During 2004–2018 a total of 289 chicks from nine different zoos were donated to the release pro- ject Waldrappteam; 128 have died while free flying and 25 returned to captivity because they were injured. Proyecto Eremita in Spain received 171 birds during the initial stage (2004–2009), and in total 423 birds from 19 different zoos (including Jerez Zoo); 202 had died by 2018. Each year 2–3 new colonies are founded in European


zoos. Besides the European Endangered Species Programme there are two further studbooks, one in Japan and one in North America, with fewer birds (110 and 140, respectively). There are an estimated 800 additional non-studbook birds of unknown parentage in other collections.


European research and reintroduction projects


The northern bald ibis was native in Europe until the Middle Ages (Kumerloeve, 1984; Pegoraro, 1996), but had become extirpated by 1650, possibly because of habitat loss, climate change and direct persecution (Schenker, 1977; Böhm & Pegoraro, 2011). It is likely the European population was mi- gratory, an idea reinforced by Conrad Gessner (1557) in his Vogelbuch description of northern bald ibis distribution, behaviour and fledging time. Centuries later, the northern bald ibis had become a mythical creature until it was re- discovered by scientists at the end of the 19th century (Rothschild et al., 1897). Three hundred years after the extinction of the northern


bald ibis in Europe, in the 1930s, European zoos started to keep the species, with the first captive breeding successes in the 1960s at Basel Zoo (Mendelssohn, 1994). From the late 1970s improved husbandry resulted in the 1,745 birds now held in 87 European zoo colonies (Böhm et al., 2018).


Austria and Germany: developing reintroduction methodologies


In 1991 Alpenzoo Innsbruck started hand raising and releas- ing northern bald ibis chicks (Thaler et al., 1993). The Konrad Lorenz Research Station (a core facility of the University of Vienna) in Grünau im Almtal established the first European free-flying sedentary (but not self- sustaining) northern bald ibis colony in 1997 (Kotrschal, 1999). This population has maintained 9–15 breeding pairs over the last 10 years (Table 5) and was a starting point for the experimental northern bald ibis restoration projects in Europe. In 2000 hand rearing was stopped, and no summer supplementary food was provided while the birds remained free flying. During 1998–2003 the birds were enclosed in the aviary during the dispersal period (July–September). Since


Oryx, 2021, 55(6), 934–946 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320000198


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