Cape Rockjumper Chaetops frenatus Scientific name definitions
Version: 2.0 — Published May 17, 2021
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Diet and Foraging
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Diet and Foraging
The Cape Rockjumper is mostly insectivorous, and spends the majority of the day foraging (4). Birds forage on the ground, looking around the base of rocks and bushes, and scuttling between patches of cover. They will also jump and kick at bushes to dislodge prey items.
While the Cape Rockjumper generally forages near other members of its territorial group (within 20 m), there is no evidence of food-sharing between adult birds. Adults sometimes try to steal prey items from other adults within the group (KNO, personal observations).
Main Foods Taken
Diet is mostly Invertebrates , occasionally small lizards, and amphibians.
Microhabitat for Food Selection
As their habitat consists of plants less than one meter tall, birds forage by constantly moving throughout its territories, travelling steadily across the mountain slope (see Behavior: Locomotion). They run along the ground, over the top of and in cracks of boulders, sometimes taking short gliding flights once prey is spotted. In general it forages mainly in the sun; as the temperature increases, birds switch to foraging mainly in the shaded microhabitats provided by the boulders, but when doing so they spends less time foraging in general (4).
Food Capture and Consumption
For more static prey items on bushes (e.g. spiders, caterpillars), birds jump and kick the bush to knock the prey item free (KNO, personal observation). More mobile prey items (e.g., grasshoppers) are chased down (KNO, personal observation). In some cases, they makes short trips out from a known food source when that source consists of small prey items — for example, a Rock Hyrax (Dassi) pellet "latrine" with small bugs around it (KNO, personal observation). For larger prey items (e.g., katydids, or beetles), birds smash the prey against a boulder to try and separate it into smaller sections while also removing some of the undigestible sections (e.g., the head and carapace; KNO, personal observation).
Main prey items brought to nests include Lepidoptera (e.g. butterflies), Coleoptera (e.g., beetles), annelid worms, Diptera (flies), Hymenoptera (e.g., flying ants or termites), Orthoptera (grasshoppers, katydids, stick insects), and Arachnids (spiders and scorpions). Less common prey items include Cordylids (flat lizards), Gekkonidae (geckos), Bradypodian (dwarf chameleons) , and Breviceps (frogs) [14; photos below are still images taken from video footage of parental nest care (9)].
Food Selection and Storage
There is no evidence that the Cape Rockjumper stores food.
Nutrition and Energetics
Metabolism and Temperature Regulation
The Cape Rockjumper's metabolism does not vary between the sexes, but both breeding and young birds are less able to handle cold temperatures when compared to nonbreeding adults (7).
It has a lower basal metabolic rate (i.e. the lowest possible metabolic rate), lower body temperature, and improved insulation in winter compared to summer (7). This probably helps reduce energy expenditure in winter when food is the most scarce (7). It also has a higher summit metabolism (i.e., the maximum metabolic rate) in winter compared to summer, which allows it to tolerate colder days when necessary (7).
Birds are in better body condition in winter than in summer (7) based on a standard measure of body mass/tarsus length. Birds in summer may be in lower condition due to higher energy demands from breeding, combined with the fact they are foraging for young as well as themselves (4).
The Cape Rockjumper shows increased efficiency at heat dissipation in summer by increasing its evaporative water loss (i.e. panting) and decreasing the metabolic rate (3). Juveniles are similar in their cooling efficiency (measured as the proportion of heat lost over heat produced), but do so at a higher water cost (2). Juveniles also cannot cope with temperatures as high as adults, as they had to be removed at lower temperatures due to signs of stress (2).
The Cape Rockjumper's summit metabolism is low for a member of the oscine Passeriformes. This may be explained by the narrow temperature range of its habitat not requiring cold-adjustment, or may be a partial indicator of itsr basal placement within passerine phylogeny (7) (see Systematics).
The Cape Rockjumper has a lower body temperature than most passerines (ca 37.5 °C) (7) compared to passerine average of ca 41.6 °C (36), with no difference between the sexes. Breeding birds have higher body temperatures than nonbreeding birds (7). Young birds have higher body temperatures than adults (2).
Drinking, Pellet-Casting, and Defecation
The Cape Rockjumper likely gets water from prey items, as birds was not recorded drinking during camera trap surveys of water sources (37).
There are no data suggesting that birds produce a pellet.
Adults have normal passerine defecation. Nestlings produce a "poop–sac" as with most passerine young, which helps adults keep the nest tidy. When removing the poop-sac, the adult often ingests the sac (see videos under Breeding: Parental Care).