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Rockjumper

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Rockjumpers
Cape rockjumper (Chaetops frenatus)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Chaetopidae
Fjeldsa, Ericson, Johannson, & Zuccon, 2015
Genus: Chaetops
Swainson, 1832
Species

Chaetops frenatus
Chaetops aurantius

The rockjumpers are medium-sized insectivorous or omnivorous birds in the genus Chaetops, which constitutes the entire family Chaetopidae. The two species, the Cape rockjumper, Chaetops frenatus, and the Drakensberg rockjumper, Chaetops aurantius, are endemic residents of southern Africa.[1] The Cape rockjumper is a resident of the West Cape and south-west East Cape, and the orange-breasted (or Drakensberg) rockjumper is distributed in the Lesotho Highlands and areas surrounding them in South Africa. The two rockjumpers have been treated as separate species but differ in size and plumage. The ranges do not overlap, but come close to doing so.

Taxonomy and systematics

Originally, these birds were placed in the thrushes, and they have also been placed with the Old World warblers and the babblers, but recent DNA studies indicate these birds are actually members of a basal group of oscines within the infraorder Passeri along with their sister-family the rockfowl (Picatharthidae), [2] Cape Rockjumper's have physiological responses that do not seem to fit with other passeridae, but may be the result of this ancient lineage. [3]

Some authorities (notably Dickinson and Christidis) treat the two rockjumpers as a single species, Chaetops frenatus, with two subspecies.[4]

Description

Both Rockjumper species are medium-sized passerines with mostly black, white, and red plumage. Both species have long, white tipped black tails, black throats, broad white submoustachial lines (malar stripes) and eyebrows, rufous or orange bellies and rumps, and grey and black patterned backs and wings. Females have similar pattern to males, but duller.[1] The iris is red and the bills and legs are black. Females are slightly smaller than males, and Drakensberg are slightly smaller than Cape (although taller, with longer tarsi). Immature birds resemble females, but lack the red iris, having one which is black.

Their wings are very small and they do not fly very often, although they will often take long gliding "flights" across valleys or downslope. They spend most of their lives running and jumping among rocks and grasses while hunting arthropods, small lizards, and amphibians.

Climate Sensitivity

Cape Rockjumpers exist only in Alpine Fynbos, a specialized habitat of 90 000 ha from Cape Town to Port Elizabeth in South Africa. These birds are alpine habitat specialists, and so used to a very specific range of temperatures. Cape Rockjumper numbers are declining in warmer parts of their habitat, and birds were found to have low heat tolerance compared to other birds of the Fynbos.[5] Juvenile Cape Rockjumpers are more sensitive to the heat than adults, and perhaps cannot drink enough water to make up for the water they lose in trying to stay cool when it's hot. [6]

Birds also struggle to continue foraging when it is hot, and produce smaller offspring at higher temperatures. [7]

Behaviour and ecology

Diet and feeding

The rockjumpers feed in groups, foraging on the ground. The groups can number up to 6 birds (for Cape) and 12 birds (for Drakensberg), but the groups may also spread out quite widely during feeding.[8][9] Insects are the major part of the diet, although small vertebrates are reported to be taken by Cape rockjumpers.[8] A range of insects are taken, including caterpillars, moths, grasshoppers, beetles and flies. In addition to insects other prey include lizards and geckos, amphibians, scorpions, annelid worms and spiders.

Breeding

They are monogamous and pairs establish territories which are defended year round. In the Cape Rockjumper the territories near Cape Town vary in size from 4–11 ha (10–27 acres), but are larger out east [10]. Both species employ helpers, usually the young of previous broods, to aid the breeding pair in raising the young.[11] While an initial study from 2002 found Cape Rockjumpers attempt only one nest per season, a more recent study found they will attempt up to 5 nests per season if initial nests fail, and even re-nesting when they have had a successful nest [12].

Open nests are built on the ground under rocky overhangs, lined with red rock rabbit fur or seeds from nearby proteacea. While Cape Rockjumpers generally lay 2 eggs compared to the Drakensberg's 3, Cape have been recorded laying 3 eggs in years with good precipitation [13]. Both sexes incubate the clutch for 19–21 days. Chicks fledge at 19–21 days, although they are fed by the parents and helpers for up to 2 weeks following fledge. Eggs are plain white.

Reproductive Success

As ground nesters, Rockjumpers face large amounts of predation. Cape Rockjumper nest predation comes predominantly from the Boomslang (Dispholydus typus), with this predation increasing at higher temperatures. They also experience predation from Cape Grey Mongooses, Honey Badgers, Common Egg-eaters, and rats [14]. While parents can deter Mongoose by harassing them, this is generally not successful to deter snakes. Although not recorded, it is also likely they experience predation from Chacma Babboons, Black-backed Jackals, White-necked Ravens, and other snakes in the area (such as Cape Cobras or Puff Adders).

Nest success for Cape Rockjumpers is higher in territories that had more recent fire (within 3-5 years), possibly as there were fewer predators present. [15]

References

  1. ^ a b del Hoyo, J.; Elliot, A. & Christie D. (editors). (2007). Handbook of the Birds of the World. Volume 12: Picathartes to Tits and Chickadees. Lynx Edicions. ISBN 978-84-96553-42-2
  2. ^ Oliveros et al. 2019 "Earth history and the passerine superradiation" PNAS. 116: 7916-7925
  3. ^ Oswald, KN, ATK Lee, and B Smit. In Review. Seasonal metabolic adjustments in an avian evolutionary relict restricted to high altitudes. J Thermal Biol.
  4. ^ Lepage, Denis. "Chaetops [frenatus or aurantius] (Rock Jumper) - Avibase". avibase.bsc-eoc.org. Retrieved 9 September 2017.
  5. ^ Milne, R., Cunningham, S. J., Lee, A. T., & Smit, B. (2015). The role of thermal physiology in recent declines of birds in a biodiversity hotspot. Conservation Physiology, 3(1), cov048.
  6. ^ Oswald, KN, ATK Lee, and B Smit (2018). Comparison of physiological responses to high temperatures in juvenile and adult Cape Rockjumpers (Chaetops frenatus). Ostrich. 89(4): 377-382.
  7. ^ Oswald, KN, B Smit, ATK Lee, CL Peng, C Brock, SJ Cunningham. In Review. Reduced body condition for older nestlings is associated with higher temperatures in a range-restricted alpine bird. An. Beh.
  8. ^ a b Collar, N., Robson, C. & Sharpe, C.J. (2017). Cape Rockjumper (Chaetops frenatus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/59691 on 4 July 2017).
  9. ^ Collar, N. & Robson, C. (2017). Drakensberg Rockjumper (Chaetops aurantius). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/59692 on 4 July 2017).
  10. ^ Oswald, KN, B Smit, ATK Lee, and SJ Cunningham (2019). Behaviour of an alpine-endemic bird is described mainly by interactions between microsite and air temperature. An Behav. 157: 177-187
  11. ^ Holmes R, Frauenknecht B, & M Du Plessis (2002) "Breeding System of the Cape Rockjumper, a South African Fynbos Endemic" Condor 104 (1): 188–192 doi:10.1650/0010-5422(2002)104[0188:BSOTCR2.0.CO;2]
  12. ^ Oswald, KN, B Smit, ATK Lee, CL Peng, C Brock, SJ Cunningham. Under review. Reduced body condition for older nestlings is associated with higher temperatures in a range-restricted alpine bird. An. Beh.
  13. ^ Oswald, KN, B Smit, ATK Lee, CL Peng, C Brock, SJ Cunningham. Under review. Reduced body condition for older nestlings is associated with higher temperatures in a range-restricted alpine bird. An. Beh.
  14. ^ Oswald, KN, EF Diener, JP Diener, SJ Cunningham, B Smit, and ATK Lee (2020). Increasing temperatures increase the risk of reproductive failure in an alpine ground-nesting bird, the Cape Rockjumper Chaetops frenatus. Ibis. 10.1111/ibi.1284
  15. ^ Oswald, KN, EF Diener, JP Diener, SJ Cunningham, B Smit, and ATK Lee (2020). Increasing temperatures increase the risk of reproductive failure in an alpine ground-nesting bird, the Cape Rockjumper Chaetops frenatus. Ibis. 10.1111/ibi.1284
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