Cape Rockjumper Chaetops frenatus Scientific name definitions
Version: 2.0 — Published May 17, 2021
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Ground nesting, presumed monogamous, facultatively cooperative.
Breeding occurs between August and December, although nest initiation can occur as early as July, and birds may have nestlings into January. This timing aligns with winter rainfall in the fynbos that results in highest insect productivity in October (40), when most territories have nestlings or even fledglings. While early studies found no evidence for re-nesting within a breeding season (15), a later study found breeding pairs will continue to nest throughout the breeding season (up to 5 nest attempts have been recorded in a single territory) (9). The discrepancy was likely due to the extreme cryptic behavior of the birds and their nests, as birds may not return to their nest for hours at a time, and new nests may be quite far from the previous nest (up to 400 meters apart on opposite edges of the territory). Birds will even re-nest after having one successful brood, although there is no evidence for more than two successful broods (KNO, personal observations).
A breeding pair begins searching for a nest site in mid-July, and begins nest building in late July or early August (with some earlier exceptions extrapolated from timing of eggs) (5; 15). In general, all territories have an active nest (either being built, with eggs, or with nestlings) by late August (for construction and location see Breeding: Nest).
The first brood is in some stage of development (eggs or nestlings) by late August. The timing can be precarious due to the potential for inclement weather (for example, late August snowfall; see Breeding: Incubation: Hardiness of Eggs) (5).
Continues re-nesting throughout the breeding season, beginning nest initiation of new nests within a week of failure of the previous nest (KNO, personal observations). The latest observed nest initiation occurred in mid-December (5). In some cases, adults continue nest attempts even after a successful brood, although there is no evidence they continue nesting after having two successful broods (KNO, personal observations). The timing between one brood fledging and another initiating is unknown.
There is very little information on nest site selection process, although as with most aspects of their breeding behavior it is presumed both the breeding male and female are involved in selecting a nest site.
Nests are built anywhere within the territory, from the center to the edge, and in some instances are built on what was considered through observation to be a territory boundary (KNO, personal observations). In one case, a group nested slightly outside what had been considered their territory for the past year of observations — they had never been observed across the valley which was assumed to separate the two territories. While the encroaching pair may have gained from the addition of the other groups' vigilance (if that group had also had a nest in the area), their nest was depredated fairly quickly (the nest was depredated 5 days after laying eggs; KNO, personal observations). The established territory's breeding pair had a recent fledgling, and had frequent disputes with the encroaching pair, perhaps drawing more attention to the area through the loud calling and displaying (KNO, personal observations; see Behavior: Agonistic Behavior).
Despite there being a wide variety of microhabitats available (i.e., varying degrees of vegetative and rock cover), there is no evidence that microhabitat affects nest success, with no correlation between amount of vegetation cover around the nest and nest success (5). Nests are generally built downslope of rocky overhangs that allow for nests to remain in the shade for most (if not all) of the day. Building downslope also allows for protection from rain runoff, as well as slight protection from wind. There is no evidence for a directional preference of the slope, possibly as many territories do not have all directions as options. The slope inclination can vary between quite shallow (ca 20°) and quite steep (ca 60°) (unpublished data).
Range-wide the typical nest site is on the ground under rocks or in rock crevices. In some cases, nests are built against a cliff face or within split rocks without quite being under an overhang (see photos), but this is rare. Nests often have two "access points" – a main opening but also a smaller opening in the back.
Nest are built by both sexes in 3 – 7 days (n = 4), with lining added for a further 5–10 days (1–2 days before egg-laying) ( 14). With few exceptions, nests are untidy bowls of grass, twigs, rushes, lichen and moss, lined with fine grass, rootlets, hairy Proteaceae seeds and mammal fur (14 ; unpublished data).
While both male and female are involved in nest building, the male often spends a fair amount of time maintaining vigilance while the female continues to build the nest, often while holding nest material in his bill (KNO, personal observations).
There are no data directly comparing ambient temperatures with conditions at the nest. However, areas of full rock shade remain cooler than the surrounding habitat (4), and so nests built under rocky overhangs providing full shade are more likely to remain cooler on hotter days.
Maintenance or Reuse of Nests
Color and Surface Texture
Generally white. Smooth, matte, unmarked.
Clutches were presumed to be 2 eggs based on ad hoc observations, a three-year study (1998-2000) (15), and the first two years (2016-2017) of a more recent study (5). However, in 2018, 12 of 31 nests (from 7 different breeding pairs) had clutches of 3 eggs (5). Clutch size does not vary with re-nesting attempt; in 2018 one female produced 5 consecutive 3-egg clutches (9), while another produced 3-egg clutches for her 3rd and 4th clutch. The difference in clutch size may be due to climate conditions, with birds in 2018 taking advantage of decent rainfall at the beginning of the breeding season (August; 5 ).
Females lay one egg per day on consecutive days (15). In one instance a male was observed perching and calling on a boulder just above a freshly-lined nest, presumably to encourage the female to come lay an egg (38). The female then glided over and immediately went into the nest. The male remained vigilant on the boulder for the next 15-20 minutes (besides making 2 quick trips into the nest) before the female emerged. On her emergence, the female glided a short distance away (ca 5 m) and began preening. The male went into the nest and then emerged and began displaying on his previous boulder before gliding over to join the female (KNO, personal observations).
Onset of Incubation
Incubation can start immediately after the first egg is laid, or may not begin until after the second egg is laid (15).
Both male and female develop a single abdominal patch (7).
Incubation usually lasts 19-21 days (average 20.3 ± 1.0 days, n = 4 nests; 15). There are no data on whether incubation period changes with clutch size, or nest attempt, as the previous study had only 2-egg clutches and no re-nesting attempts. There also is no information on whether incubation time changes with the nest attempt.
Both the male and the female of the breeding pair share incubation (15). In general, the female does not travel as far from an active nest as the male. After a bout of incubating, the female or male often flies to a nearby (ca 10 m away) lookout boulder and spend time preening and stretching (KNO, personal observations).
There are very little data on whether helper individuals aid in incubation, although in the sole instance of a supernumerary female, this helper female was recorded incubating on several occasions (15). While there is no difference in the average time the male and female spend incubating, females have far less variation in the length of incubation time (15).
Hardiness of Eggs Against Temperature Stress; Effect of Egg Neglect
There is no information on whether incubation period varies with ambient temperature. There is some evidence that adults will neglect eggs due to snow coverage possibly limiting nest access, as two nests with eggs were abandoned after a late-season (i.e., early September) heavy snowfall (5). After the snow cleared, nest checks found these nests contained cold and unviable eggs and the adults in the territory were building a new nest (KNO, personal observations). Nests with nestlings during the same snowfall event survived the extreme weather, suggesting nests with eggs may have required more investment, which adults were not willing/able to provide.
Preliminary Events and Vocalizations
Birds have been seen calling, displaying, and holding small prey items in their bill near nests that are about to hatch and ready to provision immediately on nestling emergence (KNO, personal observations).
Shell-Breaking and Emergence
Occasionally only one of the eggs will hatch. Hatching is somewhat asynchronous, with all successfully hatching eggs hatching within one day of each other (15).
Parental Assistance and Disposal of Eggshells
There is no information on whether adults aid in hatching. Adults remove eggshells from the nest area. In nests where only one egg hatches the other egg is generally no longer in the nest after a few days (KNO, personal observations), but there is no information on whether it is the adults removing the unviable/unhatched egg(s).
Condition at Hatching
Hatches with dark gray down. The bill has a lemon yellow cere and the gape is yellow with orange interior. There is no information for nestling mass at hatching.
Growth and Development
See photos below for examples. Newly hatched young are mostly naked with pink skin and fine wispy down. By 3–4 days down has darkened. By 5–8 days they are covered in dark gray down, eyes are open, and gape is bright yellow – the first contour feathers emerge. By 9 days primaries are in pin and rectrices are visible, at this point flight feathers begin to develop. At 13 days feathers cover the entire dorsal surface and begin to appear on thighs. From 14 days old until fledging, feathers continue to develop at a regular rate. Fledglings maintain downy feathers along the head for ca 1 week post-fledging (14 ; see photos below).
Average initial morning mass (ca 9:00) for nestlings age 4-7 days old was 12.49 ± 4.18 g, for nestlings 8-12 days old was 25.11 ± 4.20, and for 13-16 days old was 34.54 ± 4.64 g (9). Over an 8 hour period (ca 9:00–17:00), the daily mass change for nestlings age 4-7 days old was 1.43 ± 1.21 g (max = 4.99 g, min = −0.2 g), for nestlings 8-12 days old was 1.80 ± 1.42 g (max = 4.60 g, min = −0.78 g), and for 13-16 days old was 2.37 ± 2.02 g (max = 5.6 g, min = −2.1 g). Nestlings will begin partially fledging (i.e., leaving the nest for short periods of up to 3 h at a time) prior to fully fledging (i.e., leaving the nest completely) at around 15-16 days old. By 18–19 days old, just pre-fledging, nestlings are 48–50 g. At 2–3 days tarsi are 10–12 mm, by 18–20 days tarsi are 35–37 mm (nearly adult size) (14).
Nestlings gain less mass on hotter days, specifically at temperatures > 22.4 °C. This is likely due to an accompanying decrease in the rate adults provision at higher temperatures (9). It may also be from lower prey quality, nestlings may be losing mass via evaporation of water in an attempt to keep cool at higher temperatures, or nestlings may prioritize putting energy resources into other areas of growth such as feather development during hot weather (9).
Both parents share in nearly all duties besides egg-laying (15 ; 9). The amount of time spent in the nest decreases as nestlings age (9). There is no difference between males and females for the total amount of time spent at the nest (9).
Behavior Near the Nest
Adults are extremely cautious when within 20 m of an active nest. When returning to the nest (to incubate, brood, or provision) birds often spend up to 15 minutes at a distance of 10-20 m scanning the area. They may spend this time making short calls and making quick movements between boulders, stopping to perch on top of boulders and be vigilant. They then slowly creep closer to the nest, to within 5 m, but generally glide the remaining distance to the nest area and make a quick dash into the nest. Similarly, when they are extremely quick to leave the nest area, generally gliding directly from the nest to a boulder 5-10 m away and quickly moving to a distance of 10-20 m. They are less cautious in approaching a nest pre-laying, and sometimes perch and call on the rock under which a nest is being built (see Breeding: Nest).
Both male and female brood (see videos above), and there is no difference between the sexes in the amount of time spent brooding younger nestlings (9). Adults decrease the time spent brooding youngest nestlings at higher air temperatures (9) (see videos under Breeding: Parental Care). The addition of a helper (male in all cases) reduced the amount of time the breeding male spent brooding, but did not change the amount of time the female spent brooding (9).
There is no difference between the sexes in number of provisions or provisioning rate per hour (15 ; 9). Adults bring nestlings the same prey items they themselves eat (see Diet and Foraging: Diet), although they bring smaller prey items to younger nestlings. In a territory with a nestling and a fledgling and no helper, parents continued to provide for their one fledgling as well as the single nestling (KNO, personal observations). As in brooding, the addition of a helper (male in all cases) reduces the amount of provisioning done by the breeding male, but does not change the amount of provisions by the breeding female (9).
Adults spend time cleaning the nest and nest area on almost every nest visit, with both males and females performing cleaning duties. Nestlings produce fecal sacs that are removed or swallowed. In one instance, where the male disappeared when nestlings were 6 days old, the female could not keep up with provisioning and cleaning, and the nest was overrun by ants (KNO, personal observations). Video footage showed the nestlings trying to move away from the ants, including throwing themselves out of the nest, but they were unsuccessful and were found dead outside the nest upon return to collect the camera equipment. When filming, initially black color bands were used to identify individuals nestlings but adults were seen pecking at the legs (likely trying to "clean" the rings) before researchers instead clipped a toenail for identification (9).
Carrying of Eggs or Young
No evidence for either.
Group composition likely depends on the previous year (or year's) nesting success of the dominant breeding pair. In most cases, helper individuals are likely offspring from previous years; of six ringed nestlings (from three territories), four still were on natal territories in the following breeding season (15 ; 9). Supernumerary individuals generally stay in their natal territory for at least one full breeding season, sometimes staying throughout a second breeding season (159). In one instance of nest success early in the breeding season, the juvenile left mid-October and established nearby territories, making a nest attempt in the same season (15). In almost all cases the helper individual is a supernumerary male (41 ;
In one territory with a helper individual, the helper was observed foraging with two fledglings from an early nest while the breeding pair focused on their new nest (KNO, personal observations). In an additional three territories with a helper individual (male in all cases), the addition of a helper male only resulted in decreased workload for the dominant male (as mentioned in Breeding: Parental Care); the overall proportion of combined care provided by males was indistinguishable between groups with 2 or 3 adults (with 1 or 2 males) (9). Individual males could only be distinguished in one territory, where the helper (offspring from the previous year) provisioned 29.5% and the dominant male provisioned 24.8%, while the dominant female provided 45.7% of all provisions (9). In another territory, a female had a successful brood with one male before then initiating a further 4 nest attempts with an unattached male in the adjacent territory while the original male stayed with the fledglings (KNO, personal observations).
Brood Parasitism by Other Species
No known instances of brood parasitism.
Departure from the Nest
As the Cape Rockjumper does not have sustained flight, the nestling period ends with nestlings walking out of the nest rather than the stereotypical "fledging" (although for ease of discussion this is still referred to as fledging). Fledglings fully leave the nest at 18—22 days old (mean = 20.3) (15; KNO, personal observations). In the few days prior to leaving the nest for good, active nestlings move to the cavity entrance and sometimes beyond, taking short "partial fledging" forays away from the nest.
Growth After Departure
At fledging, young birds do not yet have full wing or tail development, although wings are somewhat developed while the tail remains undeveloped (KNO, personal observations). The yellow gape remains until fledglings are around 3 months post-fledge. Young birds attain their adult plumage at around 6 months post-fledge. Young birds have similar mass to adult females; birds ca 3 months post-fledge weighed the same as females (see Appearance: Measurements)(7).
Association With Parents or Other Young
Fledglings continue to be fed by parents for 3-6 months after leaving the nest (KNO, personal observations). During this time, they remain in juvenile plumage, resembling an adult female, but can be distinguished by a dark iris (see Appearance: Identification).
There is no well-defined immature stage. While some birds remain in their natal territory until 2-3 years of age before establishing their own territory, others move to establish their own territory within months of fledging (see Breeding: Cooperative Breeding) (KNO, personal observations; 15 ;9).