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Prodotiscus regulus (https://www.inaturalist.org/taxa/17591-Prodotiscus-regulus) is
The aim of this Post is to explain how P. regulus has come to be the only species of bird in the Cape Floristic Region (https://en.wikipedia.org/wiki/Cape_Floristic_Region) that specialises dietarily on the exudates of sap-sucking hemipteran insects (https://tcimag.tcia.org/training/sap-sucking-insects-how-they-feed-and-the-damage-they-cause/).
Like all members of its family (https://www.sciencedirect.com/science/article/abs/pii/S1095643302001307#:~:text=Birds%20ate%20significantly%20more%20new,transit%20time%20of%20256%20min. and https://pubmed.ncbi.nlm.nih.gov/12160878/), P. regulus can digest wax (https://en.wikipedia.org/wiki/Wax), as a major source of metabolic energy.
This is remarkable, because wax is
Before European arrival, there was no niche for P. regulus in the southwestern part of South Africa.
This is mainly because
Exudates of sap-sucking hemipterans are mainly of two kinds, viz.
Europeans introduced several spp. of Acacia (https://en.wikipedia.org/wiki/Acacia) from Australia to the Cape Floristic Region.
These shrubs and trees have proven to be so ecologically vigorous in their new environment that they are regarded as invasive (https://www.cabidigitallibrary.org/doi/10.1079/9781800622197.0026).
Also introduced - albeit mainly inadvertently - from various parts of the world were several hemipterans capable of sucking the sap of these acacias (https://www.perplexity.ai/search/australian-spp-of-acacia-have-5WdSTOFwQHK06p4MSWQYiw and https://en.wikipedia.org/wiki/Icerya_purchasi).
Now, for the first time in and near Cape Town (https://en.wikipedia.org/wiki/Cape_Town), there was a plentiful source of sap-sucking hemipterans and their exudates, as potential food for arboreal birds indigenous to South Africa.
In the case of honeydew, the main indigenous bird that seems to have benefited is Zosterops, a genus observed elsewhere in Africa to forage side-by-side with P. regulus (Friedmann 1955, https://repository.si.edu/handle/10088/10101 and https://scholar.google.com/citations?user=62DqSSUAAAAJ&hl=en).
Zosterops (https://www.inaturalist.org/observations?place_id=6986&taxon_id=17439&view=species) is a small-bodied passerine with the odd combination of a short, thin beak and a brush-tipped tongue. This allows it to lap up the newly-provided honeydew, in addition to its original staple diet of fleshy fruit-pulp (and -juice) and insects (https://www.researchgate.net/publication/249439178_Summer_and_winter_diet_of_the_Cape_white-eye_Zosterops_pallidus_in_South_African_grassland#:~:text=...-,The%20Cape%20white%2Deye%20is%20described%20as%20a%20generalist%20feeder,their%20diet%20(Kopij%202004)%20.).
However, this hardly changed Zosterops biogeographically, because it had been present in the Cape Floristic Region in the first place.
In the case of the waxy exudates, the only indigenous birds that might benefit were Indicatoridae.
As many as three spp. of Indicator may have been indigenous to the Cape Floristic Region, viz.
However, this genus is adapted to take wax from the nests of Hymenoptera, not from the exudates of hemipterans. This preference may be explained partly by the fact that Indicator is larger-bodied than Prodotiscus (https://en.wikipedia.org/wiki/Honeyguide).
Instead, what seems to have happened is that a small-bodied species, viz. P. regulus, entered the Cape Floristic Region for the first time during the twentieth century. This spontaneous recruitment filled the newly-provided niche.
There was no competition between P. regulus and Zosterops, because
Honeydew is not utilised by Indicatoridae, despite
The inutility of honeydew for Indicatoridae, including P. regulus, seems to be because they
What has arisen is something biogeographically remarkable, and overlooked by naturalists despite the avifauna of Cape Town, and the Cape Floristic Region, being intensively studied.
This is that
Comments
https://repository.si.edu/bitstream/handle/10088/17020/USNMP-124_3648_1968.pdf
https://www.mdpi.com/2306-7381/10/9/574
https://www.ento.csiro.au/education/insects/hemiptera.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11042284/
Hi Antoni,
Thanks for the interesting article. I first observed Prodotiscus regulus near Stanford about 25 years ago. At the time I was very surprised to find it there as there weren't many records for the region and the bird guides only showed it extending as far west as about Plettenberg Bay. I have noticed how it has spread since then and always wondered why.
Interesting that there are no records near Stanford in iNat but there are a few records from the general area in Sabap2.
Regards,
Garth
@surfinbird
Hi Garth,
Many thanks for your helpful comment.
Here's a search-image.
Prodotiscus regulus seems to resemble the dusky flycatcher, and indeed it does sally for insects, particularly the alates of termites and ants.
However, I suspect that the central skill of P. regulus is closer to the following. It creeps about in the wattle thickets and also in orchards, gleaning scale insects (https://www.homestolove.com.au/outdoor-gardening/pest-wattle-tick-scale-9816/ and https://www.abc.net.au/gardening/how-to/tackling-scale/13259902) by means of its beak, which is set at a suitably obtuse angle.
I suspect that it forages at times side-by-side with Zosterops virens capensis, the latter licking up the honeydew instead of detaching the scale insects themselves.
This unobtrusive method of foraging, and the inconspicuous association between sharp-billed indicatorid and brush-tongued zosteropid, are unlikely to be observed in the southwestern Cape unless one is actually looking out for the syndrome.
With many thanks,
All the best, Antoni
https://www.brisbaneinsects.com/brisbane_softbugs/WattleTickScale.htm
https://www.foxeslair.org/foxypress/wattle-tick-scale
https://www.agric.wa.gov.au/pest-insects/native-plant-pests?page=0%2C1
https://plantnet.rbgsyd.nsw.gov.au/PlantNet/wattle/herbiv.html
Anomalococcus indicus on Vachellia nilotica:
Full content of article available free in https://www.researchgate.net/figure/The-scale-insect-A-indicus-encrusting-Acacia-nilotica-subsp-indica-stem_fig1_258050120
Anomalococcus belongs to Sternorrhyncha: Coccoidea: Lecanodiaspididae (https://www.researchgate.net/figure/The-scale-insect-A-indicus-encrusting-Acacia-nilotica-subsp-indica-stem_fig1_258050120)
There are many families of both Sternorrhyncha and Auchenorrhyncha in which the nymphs produce both honeydew and wax.
https://www.sciencedirect.com/science/article/pii/S2213879X13000023
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691028/pdf/12065036.pdf
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