Patchiness in prey levels increases vulnerability of Critically Endangered Northern Bald IbisesGeronticus eremitaon their Syrian breeding grounds

Abstract

SummaryA small colony of Northern Bald Ibis Geronticus eremita breeding in the Syrian desert is the only wild remnant of the eastern population of this 'Critically Endangered' species. Since its discovery in 2002, the colony has not increased in size despite being protected on the breeding grounds and exhibiting good productivity until recently. Although it appears that the population is being limited during migration and/or wintering, maintaining maximum breeding productivity is a priority for saving this colony to offset poor survival away from Syria. The ibises have a large home range but forage at a relatively small number of sites within it, despite having access to larger areas of apparently suitable habitat. We sampled potential prey using transects, pitfall traps and searches under stones at sites used by the birds to compare with unused sites. Analysis showed that used sites were twice as rich in vertebrate and invertebrate prey than the surrounding areas. Prey levels halved over the course of the breeding season, but we found that they remained higher in the preferred locations compared with the unused areas. Sites closer to the breeding cliff tended to have lower levels of prey available, which perhaps explained the long commutes that the adults undertook when foraging.This work highlights the vulnerability of the birds at this site. Degradation of the patches they use could reduce food supply below critical levels and alternative sites may be hard for the birds to identify, being relatively scarce. The birds are also vulnerable to shortening of the season in which adequate food is available. There is already little time post-fledging to prepare for migration. Low food availability later in the season makes the birds dependent on key resources found around local reservoirs and these have failed recently. Breeding failures in 2008 and 2009 may have been mitigated by improved feeding conditions on the breeding area. The successful management of the site for ibises should include measures to improve their food security through range management, and possibly reservoir rehabilitation.

Effects of bio-loggers on behaviour and corticosterone metabolites of Northern Bald Ibises (Geronticus eremita) in the field and in captivity

“…A detailed discussion of these results is beyond the scope of this study. However, there is evidence from other studies that juvenile and sub-adult birds had lower foraging efficiency compared with adults and experienced individuals, which may force juveniles to migrate later than adults [47,72]. In our study, yearling juvenile birds were observed foraging more frequently than adult birds, irrespective of being equipped with a transmitter or not.…”

An assessment of ecological conditions and threats at the Ethiopian wintering site of the last known eastern colony of Critically Endangered Northern Bald IbisGeronticus eremita

“…Deaths of fully-grown and immature birds were concentrated outside the breeding grounds and the mortality rate of immature birds during the 2-4 year period before their return to the natal site (Serra et al 2009b, Serra et al in press) seems significantly higher than those recorded in similar species (Bairlein 1981, Schultz et al 1988, Menu et al 2005, Pistorius et al 2006, Gauthier et al 2010). The ecology of the Northern Bald Ibis at the Syrian breeding site is well known (Serra et al 2008, 2009b, Lindsell et al 2011) but no data are available about the species’ behavioural ecology, habitat requirements and potential threats on their wintering grounds. In the present study, we sought to determine whether conditions at the wintering site could underlie the failure of this population to improve its status in recent years (Kanyamibwa et al 1990, Berthold and Terrill 1991, Saino et al 2004).…”

Influence of feeding ecology on breeding success of a semi-wild population of the critically endangered Northern Bald IbisGeronticus eremitain southern Turkey

“…Despite being provided with sufficient supplementary food, the Northern Bald Ibises in Birecik appear to acquire much of their nutrition from wild foraging habitats, and the availability of such productive foraging habitat would be essential if new breeding stations are to be created for the species in its former range in southern Turkey. The observed foraging habitat used around Birecik has similar properties to the foraging areas found for the species elsewhere, where sparsely vegetated fallow land, cultivation, or semi-natural steppe grassland were the most preferred foraging habitats due to their higher level of prey availability (Bowden et al 2008, Serra et al 2008, Lindsell et al 2011). Such cultivations and grasslands have been used for foraging around Birecik in the past (Hirsch 1979, Akçakaya 1990), but there is no information on whether these habitats have changed as a consequence of pesticide use and whether they retain similar prey densities today as they did several decades ago.…”

“…Based on scan sampling observations of flocks encountered in wild foraging areas we documented a marked decrease in the proportion of time spent foraging throughout the season. This pattern is counterintuitive for two reasons: as chicks hatch and grow, the energetic demands on parents increase, and birds feeding chicks should therefore increase their foraging investment (Drent and Daan 1980); in addition, prey availability may decline sharply during the season (Lindsell et al 2011), which would require an increase in foraging effort to maintain similar levels of energy intake. We speculate that the apparent decrease in foraging behaviour during the season in our data may have been generated by an increasing proportion of failed breeders making up our sample of observed birds later in the season, rather than an actual decline in foraging effort during the breeding season.…”

“…In the 1970s, the birds were assumed to forage on untilled fields up to 70 km from the breeding location (Hirsch 1979), but it is possible that such long foraging flights may have been due to intraspecific competition of the much larger colony in those years (Ashmole 1963, Brown and Brown 2001, Oppel et al 2015). However, even relatively small colonies in Morocco and in Syria display regular foraging flights to highly suitable fields up to 20–35 km from the colony (Bowden et al 2008, Serra et al 2009, Lindsell et al 2011). In contrast to the birds in Morocco, the colony at Birecik benefits from a permanent source of fresh water for drinking (river Euphrates), which may permit birds to explore a wider area for foraging within a short travel time from a large water source (Bowden et al 2008, Smith et al 2008).…”