Cape Rockjumper Chaetops frenatus Scientific name definitions
Version: 2.0 — Published May 17, 2021
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Walking, Running, Hopping, Climbing, etc.
The Cape Rockjumper uses a combination of running and jumping to navigate the mountain slopes, moving quickly between, over, and around boulders, with an asymmetric running movement that vacillates between hopping and striding (KNO, personal observations; 14).
Birds have never been observed using sustained, wing-flapping flight (4). They do make short gliding trips either downslope or across valleys (often referred to as "flights" for the sake of simplicity), by spreading the tail and wings to maintain lift, or just spreading the tail to move more quickly and waiting until close to the landing spot before spreading the wings to bank and land (KNO, personal observations).
Swimming and Diving
Not known to swim or dive.
Preening, Head-Scratching, Stretching, Sunbathing, Bathing, Anting
Water bathing is infrequent, occurring immediately after rain in small pools of water that collect in boulder depressions (KNO, personal observations). More commonly, movements typical of bathing (wing shuffling, brief shakes, or fluffed plumage) accompany preening, in which the bill is run through the feathers (4). The head is scratched with the foot lifted over the drooped wing. Simple sunning behavior generally occurs at dawn when the sun first makes it past the mountains. Birds hop onto a conspicuous rock and fluff out their feathers while crouching. While foraging, birds often clean the bill by rubbing the head and bill along the boulders (KNO, personal observations).
Despite living in groups, there is no evidence of allo-preening between individuals.
Roosts as a group in rock crevices; each family group may have several roost sites within their territory (KNO, personal observations). On warm days (e.g., in the summer) goes to roost just after sunset, often in darkness, and are often up and foraging just before dawn (KNO, personal observations). On cooler days (e.g., in winter) often waits until the sun is out before beginning to forage, first spending time sunning (KNO, personal observations).
Daily Time Budget
Overall, spends most of the day foraging (4). As the temperature increases, it spends more time in the shade provided by the many boulders. Birds in the shade pant less, saving both water and energy, potentially providing a behavioral buffer against the heat (4). Shows decreased levels of both activity and foraging while in rock shade. This suggests that while any potential direct impact of temperature is mediated by the change in microsite use, seeking shade might involve a trade-off against foraging or maintaining activity levels (4).
Females spend more time foraging than males, while males spend more time preening and vigilant than females. Nonbreeding birds spend more time preening than breeding birds, possibly in preparation of the breeding season (4).
Territorial defense is highest from August to November (during the breeding season) when all individuals in a group increase their aggressiveness toward any encroaching bird (KNO, personal observations; 15). Defense involves both auditory and visual displays, as well as extensive chasing and interactions along boundaries. Both sexes run or hop to the top of the nearest boulder or rocky outcrop, giving short, often two-note whistles or a loud series of whistles. Individuals may display on large boulders with heads held up and tail fanned low exposing conspicuous white spots, while giving the two-parted alarm call (KNO, personal observations). They then glide over the rocky terrain in pursuit of the intruders. Physical disputes include jumping feet-first at one another with wings and tails spread. Nearly every agonistic display involves calling and tail-spreading. On occasion, also may try to "steal" food from one another. All individuals in a group may become involved in territorial defense (16), although observations suggest males are more aggressive to other males, and females are more aggressive to other females (KNO, personal observations).
No interspecific encounters have been observed between the Cape Rockjumper and other non-predatory species.
Mating System and Operational Sex Ratio
Usually socially monogamous, but group composition suggests the potential for polyandry or polygyny. While there is no direct evidence for polygyny, there is mild evidence for polyandry: in 2018 a female had a successful brood with one male before then having another four (unsuccessful) nest attempts with a different unattached male in the adjacent territory (KNO, personal observations).
Likely a male-biased sex ratio based on groups generally consisting of more males than female (4 ; 16 ; 15), possibly due to female dispersal (see Movements and Migration: Dispersal) resulting in higher female mortality.
Courtship, Copulation, and Pair Bond
The courtship display is still unknown or unrecognized as such.
As birds re-nest multiple times in a single breeding season (see Breeding: Phenology), copulation has been observed occurring regularly throughout the breeding season as birds continue re-nesting (KNO). Both individuals seem to be involved in solicitation. After arriving at the same boulder, the male and female begin to call to one another, displaying with tails fanned. Afterwards the female quivers her wings clear of the body and the male quickly mounts her for copulation. Following copulation, the pair often stays and preens beside one another (KNO, personal observations).
For about a week before laying eggs, the female is guarded closely by her mate, who often perches on a nearby conspicuous boulder and preens while maintaining vigilance (KNO, personal observations).
Both male and female are involved in nest site selection, as well as nest-building (KNO, personal observations). The male often is more conspicuous during this time period, sometimes perching on the boulder under which the nest is built (see Breeding: Nest) and calling repeatedly with tail spread (KNO, personal observations). In one instance the male was observed soliciting the female to lay an egg, by remaining near the nest and calling (38). She then arrived and entered the nest to lay an egg, during which time he maintained vigilance by the nest and occasionally would go into the nest area. After laying, the female moved a short distance away to preen while the male maintained vigilance at the nest (38). In another instance two males chased and called after a female, with the female cornered among rocks and mounted by one male. The second male did not pursue once the female had already mated (14).
Extra-Pair Mating Behavior/Paternity
There is no information on extra-pair copulation.
There is no known intra- or interspecific brood parasitism.
Social and Interspecific Behavior
Degree of Sociality
Birds are highly social within their small family groups of 2–5 individuals (4; 16; 15). It is rare to see an individual bird more than ca 20 m away from other group members, and birds generally forage within 10–20 meters of one another (KNO, personal observations). Birds do sometimes become separate by more than 20 m, usually while foraging. If this happens it is generally for a short period of time, after which one group member will initiate a re-gathering of the group through a series of contact calls. When birds re-group they call to one another and often display (KNO, personal observations).
There is no direct evidence of play. Birds sometimes chase after one another if one individual has a large prey item, but it is unknown if this is play or aggression (KNO, personal observations).
Nonpredatory Interspecific Interactions
It is often followed by other species as they forage (KNO, personal observations). Observed species include the Ground Woodpecker (Geocolaptes olivaceus), the Sentinel Rock-Thrush (Monticola explorator), the Cape Rock-Thrush (Monticola rupestris), and the Cape sengi (rock elephant shrew, Elephantulus edwardii). It is assumed this is because the Rockjumper stirs up smaller prey items. In addition, many species will come investigate when the playback of rockjumper vocalizations playback is used, e.g., the Familiar Chat (Oenanthe familiaris), the Orange-breasted Sunbird (Anthobaphes violacea), and the Cape Siskin (Crithagra totta) (KNO, personal observations).
It is quick to defend their territories from other Cape Rockjumpers, but there is no evidence it shows aggression toward other species.
Kinds of Predators
Its habitat is home to a wide variety of potential predators. These include avian predators (e.g., the Rufous-breasted Sparrowhawk Accipiter rufiventris, the White-necked Raven Corvus albicollis), snake predators (e.g., the boomslang Dispholydus typus or the Cape cobra Naja nivea), or mammalian predators (e.g., the Cape gray mongoose Galerella pulverulenta, the chacma baboon Papio ursinus). Egg and nestling predation has only been observed from terrestrial predators (e.g., mongoose, snakes), whereas predation of juveniles and adults also can occur from aerial predators.
It is assumed that most adult predation comes from birds of prey, with adults keen to alarm-call any medium–large flying bird (16). Birds alarm-calling the Rock Kestrel (Falco rupicolus) were thought to be mis-identifying them as the Rufous-breasted Sparrowhawk until a Rock Kestrel was observed attempting to grab a Cape Rockjumper that had been caught in a spring-loaded snap trap (39). Adult birds have been seen on boulders adjacent to a boomslang (within 2–5 m) with no agitation or alarm-calling during the nonbreeding season (16), but will actively try and deter boomslang during the breeding season, suggesting boomslang may not prey on adult birds despite being major nest predators (see below).
As a ground-nesting bird, experiences high levels of predation. Not including partial predation, one study found 69% nest failure in 1999 (n = 16 of 32 nests during the egg stage, and 3 of the remaining 16 nests during the nestling period) (15), while another recorded 85.2% nest failure from 2016-2018 (n = 46 of 54 nests; 24 during the egg stage, 22 during the nestling period) (5). Predation by mammals was more often seen earlier in the season (mainly August-October) whereas snake predation occurred predominantly later in the season (beginning late September through to December; unpublished data).
The majority of observed nest predation has been by boomslangs (5). Video footage suggests boomslang find the nest using olfactory senses as opposed to visual, and the snake often circles the nest area multiple times before locating the nest itself (see video below). During the breeding season, adults alarm call any boomslang within their territory (KNO, personal observations). Despite alarm-calling and mobbing boomslang near the nest, cameras indicate that birds can not successfully deter a boomslang once it has found a nest (5). While adults will continue to mob and alarm-call boomslangs the entire time they are preying upon eggs/nestlings, no adults have been observed falling prey to boomslangs in such circumstances (KNO, personal observations).
A fair amount of nest predation also comes from the Cape gray mongoose. However, adult birds have been seen successfully driving off mongooses by mobbing and alarm-calling (5).
Other nest predation was observed by the honey badger (Mellivora capensis), rats (Otomys spp.), and the common egg-eater (Dasypeltis scabra) (5). Egg-eaters may be responsible for many undocumented nest predation events, or partial predation events, but are small snakes (less than 50 cm long) and nocturnal so these events are difficult to observe and likely were missed by cameras (5).
Nest predation was less likely in territories that had more recently burned (5). Two possibilities were suggested for the greater nest survival in a more open predator landscape: (1) increased habitat visibility allowed adults to spot predators before they were able to sense the nest or (2) recently burned areas may have fewer predators. See Figure 1 (below), originally published in Oswald (5).
Response to Predators
A Rockjumper will not enter another Rockjumper's territory to aid in mobbing a predator. However, if the altercation is close enough to an adjacent group for them to be aware of the predator, they will sometimes join in alarm-calling while remaining within their territory bounds (KNO, personal observations).
When a potential aerial predator is spotted by a group member, all individuals will immediately give a series of alarm calls (16) and all members of the group will hide in rock overhangs or crevices. After a short time, birds will take surreptitious glances out from their hiding spots and emerge when the aerial predator is no longer visible (KNO, personal observations).
In one instance, a pair of Rockjumpers had a pair of Rock Kestrels nesting within their territory during the breeding season. Instead of moving territories or foraging on the other side of the valley the Rockjumpers often foraged near the Rock Kestrel nest and were in a near-constant state of alarm-calling (KNO, personal observations).
Early reactions to terrestrial threats, including approaching humans (16), are to alarm call and move swiftly to another location, preferably across a valley when possible. During the nonbreeding season, birds alarm-call any predator in their territory, but move away from terrestrial predators as opposed to staying and mobbing (KNO, personal observations).
During the breeding season, birds will remain close to the nest when a predator is spotted (KNO, personal observations). If the threat approaches an active nest, all group members will engage in alarm-calling. Birds will actively mob smaller mammals (such as mongooses) but will not actively mob humans. Instead, they will maintain a distance of generally around 2 m, and continue alarm-calling from atop a boulder until the human is more than 10 ms away from the nest (KNO, personal observations).
Nestlings react to adult alarm-calls by laying low in the nest and keeping quiet (KNO, personal observations). Video footage shows this is not successful for boomslang predation, although in one instance a boomslang missed one nestling when it depredated the nest of two of three nestlings (5). However, the third nestling was also predated on by a boomslang (possibly the same individual) 5 days later (5).