Saddle-billed Stork Ephippiorhynchus senegalensis Scientific name definitions
Version: 2.0 — Published June 25, 2021
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Walking, Running, Hopping, Climbing, etc.
When foraging, it walks slowly at a rate of 0.7–1.0 steps/s, with strides measuring 0.8–1.2 m (10).
Despite its size, it can take flight rather quickly with rapid, powerful wing flaps, and once in flight it usually soars on thermals (4). When flying it keeps its neck and feet fully extended, and its length leads it to fly in a somewhat "bent position with head and feet lower than the body" (87). Its average flapping rate is 150/min (88).
Preening, Head-Scratching, Stretching, Bathing
Pairs roost together in trees (2), but it is also known to spend the night standing in shallows pans where trees are limited (U. Bryson, personal communication; JG).
Despite numerous sources that describe the species as "basically territorial" (see 2, 4, 89), there is no empirical evidence regarding this. Indeed, it occurs at low densities and in pairs, so some level of territoriality likely occurs during the breeding season, but information beyond speculation is lacking. Outside the breeding season, aggressive territorial behavior is not apparent given the number of large congregations observed across the continent.
Spatial use, including territory size and configuration, has never been studied. This is an area of research that is very much needed to understand variation in population density and overall temporal and spatial dynamics.
Monogamous pair bonds are thought to be long-term, possibly for life, because pairs usually remain together throughout the year and do not always exhibit courtship displays when establishing a nest (10). However, the length of pair bonds has never been empirically described. Simple photo mark-resight of the unique bill patterns of individuals could be used to address this knowledge gap at regularly used nest sites.
Courtship, Copulation, and Pair Bond
Observations of newly-formed pair courtship are lacking, but probably involve displays like those described below. Because pair formation probably does not occur each season, established pairs do not necessarily exhibit courtship displays upon arriving at a previously-used nest. Interactive displays are limited to pairs away from the nest and most notably involve a flap-dash display. In this performance, one member of the pair suddenly stands erect and then runs, usually through water, with long strides while flapping its wings. The performing stork dashes away from its mate and then dashes back within a meter or two and stands with wings extended for several seconds. Sometimes the performer snaps its bill in the water near the end of a dash, picking up vegetation or nothing.
Sexual behavior of the Black-necked Stork (Ephippriohynchus asiaticus) has been more extensively described than for Saddle-billed Stork, but Kahl (10) suggested the following behaviors are likely identical between the two species.
The up-down display is a greeting display given by both sexes when one returns to the nest. During the display, each stork keeps their body and neck erect, fully open their wings and flutter them rapidly, and clatter their bills rapidly while facing one another. Similar low-intensity displays are sometimes given away from the nest, which suggests it is a common behavior for strengthening the pair bond.
Copulation may begin without any preliminary behavior, or the female may solicit the male to mount by standing with the body horizontal and pressing against his body. The male then steps onto her back from one side and hooks his toes over her shoulders, bending his legs to lower himself to allow cloacal contact. The female holds her wings open fully for the extent of copulation and the male slowly flaps for balance. Throughout copulation, the male shakes his head and clatters his bill loudly and slowly alongside the female's bill.
Social and Interspecific Behavior
Degree of Sociality
This species occurs either solitarily, in pairs, or in family groups, so generally it is not considered highly social. However, in certain environmental conditions, namely low water levels and the concentration of aquatic prey, large groups can form (see Movements and Migration: Movement), including with other waterbird species. In such cases, groups are merely incidental to the foraging conditions and are not formed for social reasons.
Nonpredatory Interspecific Interactions
Kahl (10) observed an immature Saddle-billed Stork threaten a group of Yellow-billed Stork (Mycteria ibis) that were feeding nearby. The immature stork opened its wings completely, lifted its bill slightly, and clattered its bill slowly while approaching the other retreating storks. This behavior is similar to a defense display exhibited by chicks (see Predation). Although published accounts of other such interactions are lacking, this probably occurs in certain foraging situations. Nevertheless, this species is often observed feeding alongside other waterbird species without any hostility. The kleptoparasitic African Fish-Eagle (Haliaeetus vocifer) is known to steal fish captured by Saddle-billed Storks.
Kahl (10) also described Village Weavers (Ploceus cucullatus) establishing a nesting colony around a stork nest in Kenya after the storks had been there for some time, suggesting the presence of the defensive storks provided protection to the weavers.
Kinds of Predators
There are no published accounts of predators killing a Saddle-billed Stork, but one video from South Africa showed a Martial Eagle (Polemaetus bellicosus) with a juvenile it had apparently killed. In one case in Kenya, African Fish-Eagles were reported taking and eating eggs two days after they were laid, resulting in breeding failure for the pair that year (D. Turner, personal communication).
Response to Predators
When an intruder, such as a raptor, approaches the nest, chicks will exhibit a defense display in which they stretch out their necks vertically, hold their bills horizontally, clatter slowly, open the wings fully, and puff up the feathers of the head, neck, and upper back (10).