Schenker, A., Cahenzili, F., Gutbrod, K.G., Thévenot, M. & Erhardt, A. 2019. The Northern Bald Ibis Geronticus eremita in Morocco since 1900: Analysis of ecological requirements. Bird Conservation International.
This paper analyses ecological conditions of the 72 breeding sites of the Northern Bal Ibis (NBI) that have been known since 1900 in Morocco. In 1940, the NBI population consisted of about 1,500 birds. However, it declined to about 600 individuals in 1975, including 198 breeding pairs dispersed over 13 breeding sites. Thus, only four colonies have survived on the Atlantic coast in south-west Morocco, three in the Souss-Massa National Park (SMNP) and one in Tamri. Finally, the creation of the SMNP in 1991 and conservation measures implemented since 1993 resulted in an increase of the last wild NBIs from 59 breeding pairs in 1997 to 147 breeding pairs and a total of 708 individuals in 2018, including non-breeding and juvenile birds. In 2017, two new small breeding colonies on the Atlantic coast north of Tamri were discovered and in 2018 two additional new sites were found in the SMNP on the Atlantic coast.
Breeding colonies were dispersed over all of Morocco excluding the central Rif Mountains and the eastern steppe plateau. However, a higher concentration of breeding colonies is found along the Atlantic coast, in the Souss-Massa region and in the Haha country (n = 14, 19%), in the Middle Atlas (n = 14, 19%), in the western High Atlas and the foothills of Haouz and Jbilet hills (n = 10, 14%) and in the plains and hills of Eastern Morocco (n = 8, 11%). The few known breeding colonies in the surroundings of cities (Rabat-Salé, El-Jadida, Safi, Meknes and El Hajeb) had disappeared already by the 1960s, whereas breeding colonies in more remote sites survived for longer.
The most frequent type of breeding sites are cliffs on the Atlantic and Mediterranean coasts, followed by steep slopes of perennial rivers and dry valleys, gorge-like structures and transverse valleys. However, escarpements and hogback mountains are additional important breeding sites. The most important breeding sites since 1977 are cliffs on the Alantic coast, steep riverbanks and gorge-like structures, from sea level up to 2,000 m in the Middle Atlas. However, the majority of the breeding colonies occurred below 1,000 m and most of the breeding colonies remaining since 1977 were also located below 1,000 m.
In the majority of the breeding sites known since 1900, mean annual precipitation from 1986–2016 did not exceed 300 mm. For most of the breeding sites still existing after 1977, annual precipitation was less than 300 mm. Twelve breeding sites on the south-west coast of the cold Atlantic Ocean benefit from frequent coastal fog and the formation of dew, which improves the ecophysiological conditions in this semiarid to arid coastal area.
Breeding colonies are often located at the transition zone of two distinct landscape types such as plains and foothills of the High Atlas, plains and isolated hills and plateaus and hilly area. Plains bordering hills and mountains are mostly used as agricultural land, whereas extensively grazed pastures and areas with sparse vegetation dominate in the foothills of mountains, isolated hills and plateaus. In the vicinity of breeding sites along the steep cliffs of the Atlantic coast, a small strip of coastal steppe is present.
Steep rock faces with suitable ledges and small cavities are essential habitat structures for breeding colonies of the NBI. Such breeding sites are frequently present at cliffs along the coasts of the Atlantic Ocean and the Mediterranean Sea, and furthermore in areas with calcareous rock. In inland Morocco, steep rock faces and valleys with gorges and steep riverbanks are the preferred nesting sites. Water bodies in the vicinity of the breeding colonies obviously favour breeding success.
Following elevation and climatic conditions, egg deposition begins at the end of February and the beginning of March at the Atlantic coast , but is delayed until April in the formerly occupied Middle Atlas.
Appropriate feeding grounds in the vicinity of the breeding sites are essential for the long-term survival of NBI colonies. Such feeding grounds are treeless, extensively grazed summer pastures in the Middle Atlas and traditional rain-fed agriculture and fallow land. The preferred feeding ground along the Atlantic coast is a narrow strip of sandy littoral steppe and fallow land. The three potentially suitable forage habitats of the NBI are present in a substantial proportion of the 28 breeding colonies still in existence after 1977.
Breeding colonies still persisting since 1977 are often located in remote, less disturbed areas in semiarid regions or in regions in the Middle Atlas where traditional agriculture and extensive grazing are still in use. However, breeding sites in arid regions must be considered refuge sites with reduced habitat quality due to the high variability of annual rainfall.
The four remaining breeding colonies today (three at SMNP and one near Tamri) have no particular habitat characteristics that differ from the original sites. All actual colonies are located on sea cliffs, below 500 m, close to water bodies with rainfed agriculture and fallow land and extensive pastures in the nearby surroundings. However, they differ clearly in the amount of annual rainfall (Tamri: average about 240 mm, SMNP: average about 140 mm). The main factors in their survival was their remoteness from civilization and that they were protected since 1995 by an efficient observation system with wardens. The low amout of rainfall at SMNP means that the three colonies located in this reserve are actually living under rather marginal ecological conditions. In contrast, the colony at Tamri has better ecological conditions with a higher amount of annual rainfall. The two new colonies found in 2017 are also located in the same coastal region as the Tamri colony.
Conclusions for conservation
Effective protection measures in south-west Morocco during the last two decades have not only prevented a further decline of the last wild population of the NBI, but have even caused a steady growth of these populations. Maintaining the wardening system is important and essential for the recovery of the population. In 2017, two new sites with small breeding colonies were detected on the Atlantic coast. Further foundations of new populations on the Atlantic coast or in inland Morocco seem possible, even if such sites seem hard to predict at present.
The most desirable outcome would be natural, spontaneous recolonisation of still appropriate breeding sites in Morocco. However, natural recolonisation, particularly in inland Morocco, may be slow or not occur at all. Thus, additional measures including translocation projects may be necessary. The assessment of former breeding sites in Morocco revealed two positive key factors:
(I) No human disturbances in the immediate vicinity of the nesting sites and (II) suitable feeding habitats within a relatively short distance of 5–15 km.
Based on the earlier distribution of breeding colonies (see Figure 1) in the years after 1960 and 1970, three regions for successful long-term establishment of a NBI population can be identified, the Atlantic coast with adjacent areas in the south-west of Morocco, the western Middle Atlas and the north-eastern Moulouya valley with adjacent plains and scattered island-like hill ranges.