No evolutionary convergence in the vertebrate-eating birds of Australia and southern Africa

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I have shown, in previous Posts, that there is negligible evolutionary convergence (https://en.wikipedia.org/wiki/Convergent_evolution) between Australia and southern Africa, in:

The intercontinental differences are particularly great for vertebrate-eating mammals: one small dasyurid vs a whole guild of herpestid, viverrid, felid, canid, and hyenid species.

Interpreting these anomalies is complicated by the isolation of the island continent. It is hard to distinguish the poverty of the resources in nutrient-poor Australia from the coincidence of geographical isolation.

For example, all the indigenous, fully terrestrial, vertebrate-eating mammals throughout Australia - with the exception of one species of bat (https://en.wikipedia.org/wiki/Ghost_bat) - are marsupials; and an important family (Lamprophiidae, https://en.wikipedia.org/wiki/Lamprophiidae) of snakes is absent from Australia.

So it remains possible that the ultimate cause of the faunal anomalies is phylogenetic constraints, rather than differences in the non-biotic environments (climates and soils).

Volant birds can cross seas barring mammals, and they can survive shortages by moving around within a given landmass. And indeed it is the vertebrate-eating birds that have produced the avian species most naturally widespread on Earth: Falco peregrinus (https://en.wikipedia.org/wiki/Peregrine_falcon).

Therefore, the isolation of Australia - and the associated phylogenetic constraints - should be far less confounding for birds than for snakes or mammals.

Here, I compare the vertebrate-eating avifaunas of Australia and southern Africa, within the same framework as for the previous Posts.

To make intercontinental comparison as rigorous as possible, I have chosen study areas carefully matched in climates, landforms and soils: Fitzgerald River National Park (https://en.wikipedia.org/wiki/Fitzgerald_River_National_Park) and its environs in Western Australia and Agulhas National Park (https://en.wikipedia.org/wiki/Agulhas_National_Park) and its environs in South Africa.

I have restricted the avifaunal lists to species taking vertebrates as more than half of their diets, by volume. I.e. by 'vertebrate-eating' I mean 'eating mainly vertebrates'.

The results:

The vertebrate-eating birds show far greater correspondence between continents than do the vertebrate-eating mammals. In both study areas there are large eagles, small eagles, falcons/kestrels, kites, harriers, goshawks, and the same two families of owls - including a shared species, the barn owl. Furthermore, in most cases the intercontinental counterparts are congeneric.

Based on the overall relatedness of the two avifaunal lists, we would expect that any remaining incongruities would have been relatively easily corrected by natural selection. That is to say, this test of evolutionary convergence sets rather low standards compared to those performed on snakes and mammals.

Nonetheless, the remaining differences are so obvious that, once again, negligible evolutionary convergence is actually evident.

A parallel with my previous study of the snakes is that there is more differentiation in the avifauna of vertebrate-eating birds in the southern African than in the Australian study area.

The following, found in the southern African study area, have no counterparts in the Australian study area:

  • Sagittarius serpentarius, an eagle-like form specialised for terrestrial foraging,
  • Buteo buteo, which is migratory,
  • Ardea melanocephala, a specialised heron eating vertebrates including on dry land,
  • Bubo capensis, a large terrestrial owl, and
  • Gyps coprotheres, a large, specialised scavenger.

On the converse side:

The only species found in the Australian study area, with arguably no true counterparts in the southern African study area, are:

  • Lophoictinia isura, a kite associated with the canopy of patches of eucalypts, but otherwise similar to Milvus migrans and Polyboroides typus in the southern African study area, and
  • Falco berigora, a remarkably generalised falcon that can be interpreted as a diminutive counterpart to Buteo rufofuscus - and in any case belongs to a genus well-represented in both study areas.

A noticeable pattern is that Falco and strigid owls are diminutive in Australia relative to southern Africa, in the context of this focus on vertebrate-eating species.

The Australian study area has counterparts for both Falco biarmicus and Buteo rufofuscus, but at a fraction of the body mass: Falco longipennis and Falco cenchroides.

Ninox boobook is only half the body mass of Bubo africanus.

(The small-bodied species in the southern African study area, namely Falco rupicolus (https://www.inaturalist.org/taxa/472764-Falco-rupicolus) and Ciccaba woodfordi (https://www.inaturalist.org/taxa/19965-Strix-woodfordii#Habits_and_ecology), eat mainly invertebrates.)

An alternative way of interpreting the small-bodied species of Falco in the study areas is as follows:

On each landmass there are closely related kestrels and hobbies. These qualify as vertebrate-eating birds in the Australian study area, where larger-bodied members of the same guild are not competitive owing to limited quantity and reliability of prey. However, in the southern African study area - where Falco biarmicus and Buteo rufofuscus are indeed competitive - the small forms are either

However, the pattern is inconsistent because, in the case of Circus and to a slight degree Elanus, it is the southern African species that are the smaller-bodied ones.

Geographical isolation hardly explains the lack of certain vertebrate-eating vertebrates in Australia. This is best illustrated by

Milvus migrans is extremely widespread, extending to much of Australia (subspecies affinis, https://onlinelibrary.wiley.com/doi/full/10.1111/jav.02822).

This species penetrates to the southwestern tip of Africa but not to similar latitudes in southwestern Australia.- suggesting a difference in the productivity of prey. Is Fitzgerald River National Park and its environs too poor in various vertebrates to support more than a limited and rather generalised fauna of predators and scavengers?

In the case of Elanus, the southern African species (E. caeruleus) has actually reached Australia.

Elanus caeruleus occurs in southernmost New Guinea, separated from the island continent by only the narrow Torres Strait. Given that this water was broad dry land for most of the Pleistocene, E. caeruleus almost certainly occurred previously in at least northern Australia.

Hence the fact that a different species of Elanus occurs today in the Australian study area

  • can hardly be attributed to isolation, and
  • has little adaptive meaning given that, apart from the barn owl, the most precise matching of counterparts in this study is that in Elanus: lookalike species that seem virtually interchangeable.

In summary:

There is considerable correspondence between continents in the vertebrate-eating birds. However, this similarity has been achieved mainly by faunistic recruitment, rather than by evolutionary convergence in the sense of adaptive modification of the recruits.

The vertebrate-eating avifaunas in and near Fitzgerald River National Park in Western Australia, and Agulhas National Park in South Africa, are remarkably similar phylogenetically, at the level of family, genus and even species. However, the remaining differences in form and function - and phylogeny in the cases of heron, vulture and secretary bird - are as important as the similarities.

It remains unclear whether the evident shortfall in convergence here is owing to

  • residual differences in the environments - limiting the productivity and reliability of prey in Australia, or
  • a failure of the adaptive process, i.e. of evolutionary modification by natural selection.

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AUSTRALIA: species occurring in and near Fitzgerald River National Park

Accipitridae:

Accipiter cirrhocephalus female 218 grams https://www.inaturalist.org/taxa/5138-Accipiter-cirrocephalus

Accipiter fasciatus female 355 grams https://www.inaturalist.org/taxa/5114-Accipiter-fasciatus

Circus approximans female 870 grams https://www.inaturalist.org/taxa/5168-Circus-approximans

Circus assimilis female larger-bodied than southern African counterpart https://www.inaturalist.org/taxa/5175-Circus-assimilis

Elanus axillaris female 300 grams https://www.inaturalist.org/taxa/5276-Elanus-axillaris

Lophoictinia isura female 590-680 grams mean 635 grams https://www.inaturalist.org/taxa/5286-Lophoictinia-isura and https://www.birdlife.org.au/afo/index.php/afo/article/viewFile/927/906

Haliastur sphenurus female 750-1000 grams, or mean 830 grams https://www.inaturalist.org/taxa/5407-Haliastur-sphenurus

Falconidae:

Aquila audax female 3-5.8 kilograms https://www.inaturalist.org/taxa/5080-Aquila-audax

Falco berigora berigora female 520-840 grams, mean 681 grams https://www.inaturalist.org/taxa/4680-Falco-berigora and https://www.une.edu.au/__data/assets/pdf_file/0010/24211/mcdonald-et-al-2012.pdf and https://bioone.org/journals/Journal-of-Raptor-Research/volume-40/issue-3/0892-1016(2006)40[228:TBDODB]2.0.CO;2/THE-BREEDING-DIET-OF-DIFFERENT-BROWN-FALCON-span-classgenus-speciesFALCO/10.3356/0892-1016(2006)40[228:TBDODB]2.0.CO;2.full

Falco cenchroides cenchroides possibly qualifies as vertebrate-eating female 115-273 grams https://www.inaturalist.org/taxa/4681-Falco-cenchroides and https://absa.asn.au/wp-content/uploads/2017/05/V41_P27-31_FalconDiets_Tsang_v3.pdf

Falco longipennis longipennis female 290 grams https://www.inaturalist.org/taxa/4663-Falco-longipennis and https://search.informit.org/doi/10.3316/INFORMIT.604341808414911 and https://www.birdlife.org.au/afo/index.php/afo/article/viewFile/2176/2196

Falco peregrinus rare in study area female 0.7-1.5 kilograms https://www.inaturalist.org/taxa/4647-Falco-peregrinus and https://www.researchgate.net/publication/332040949_Diet_of_the_Peregrine_Falcon_Falco_peregrinus_in_inland_south-western_Australia

Hieraaetus morphnoides female about 825 grams https://www.inaturalist.org/taxa/5150-Hieraaetus-morphnoides

Strigidae:

Ninox boobook ocellata female 300 grams https://www.inaturalist.org/taxa/979816-Ninox-boobook

Tytonidae:

Tyto alba deliculata female ?600 grams https://www.inaturalist.org/taxa/20445-Tyto-alba

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SOUTHERN AFRICA: species occurring in and near Agulhas National Park

Accipitridae:

Accipiter tachiro female 279-510 grams https://www.inaturalist.org/taxa/204453-Accipiter-tachiro

Buteo buteo vulpinus migratory female 710-1180 grams https://www.inaturalist.org/taxa/204472-Buteo-buteo and https://sabap2.birdmap.africa/docs/sabap1/149.pdf

Buteo rufofuscus female 1150-1700 grams, mean 1530 grams https://www.inaturalist.org/taxa/5198-Buteo-rufofuscus

Circus maurus female 550 grams https://www.inaturalist.org/taxa/5174-Circus-maurus

Circus ranivorus female probably less than 500 grams, smaller-bodied than Australian counterpart https://www.inaturalist.org/taxa/5165-Circus-ranivorus

Elanus caeruleus caeruleus female 230 grams https://www.inaturalist.org/taxa/5275-Elanus-caeruleus and https://journals.co.za/doi/pdf/10.10520/AJA0012723X_2116 and file:///C:/Users/Antoni%20Milewski/Downloads/151413-Article%20Text-397314-1-10-20170210.pdf and file:///C:/Users/Antoni%20Milewski/Downloads/Mendelsohn_John_M_1982.pdf

Gyps coprotheres https://www.inaturalist.org/taxa/5365-Gyps-coprotheres

Milvus migrans parasitus rare in study area female 560 grams (or 592 grams in Australia) https://www.inaturalist.org/taxa/5268-Milvus-migrans

Polyboroides typus rare in study area https://www.inaturalist.org/taxa/5246-Polyboroides-typus and https://www.tandfonline.com/doi/abs/10.1080/00306525.1981.9633580

Ardeidae:

Ardea melanocephala https://www.inaturalist.org/taxa/4972-Ardea-melanocephala and https://www.degruyter.com/document/doi/10.2478/s11756-006-0037-5/html

Falconidae:

Aquila verreauxi rare in study area female 3-7 kilograms https://www.inaturalist.org/taxa/5077-Aquila-verreauxii

Falco biarmicus biarmicus female 850 grams https://www.inaturalist.org/taxa/4684-Falco-biarmicus

Falco peregrinus rare in study area female 0.7-1.5 kilograms https://www.inaturalist.org/taxa/4647-Falco-peregrinus

Hieraaetus pennatus rare in study area female 840-1025 grams https://www.inaturalist.org/taxa/5154-Hieraaetus-pennatus and https://sabap2.birdmap.africa/docs/sabap1/136.pdf

Polemaetus bellicosus rare in study area female about 4 kilograms https://www.inaturalist.org/taxa/5344-Polemaetus-bellicosus

Sagittariidae:

Sagittarius serpentarius 3.7-4.3 kilograms mean 4.0 kilograms https://www.inaturalist.org/taxa/117214-Sagittarius-serpentarius

Strigidae:

Bubo africanus 454-904 grams https://www.inaturalist.org/taxa/204470-Bubo-africanus

Bubo capensis rare in study area female 1240-1800 grams https://www.inaturalist.org/taxa/20095-Bubo-capensis and https://sabap2.birdmap.africa/docs/sabap1/400.pdf

Tytonidae:

Tyto alba affinis (large-bodied subspecies) female ?700 grams https://www.inaturalist.org/taxa/20445-Tyto-alba

Publicado el marzo 8, 2022 03:49 MAÑANA por milewski milewski

Comentarios

Buteo rufofuscus includes snakes in its diet, including venomous ones up to 1 meter long. This may seem similar to its approximate Australian counterparts Falco berigora and Haliastur sphenurus, which also eat snakes. However, in B. rufofuscus "the toes are thick and stubby, and the scales on the toes and bare tarsus are large and coarse. These features may be an adaptation related to catching snakes and other difficult ground quarry, as similar types of feet are found on other snake-eating raptors such as the laughing falcons (Herpetotheres sp.), snake eagles (Circaetus), and some others". Reference: Cade T J (1982) The falcons of the world. Collins, London, 188 pp. Furthermore, Buteo rufofuscus is far larger-bodied than the Australian species, and double the body mass of F. berigora.

Publicado por milewski hace casi 2 años

@tonyrebelo @ludwig_muller Hi Tony and Ludwig, Happy ending, I have successfully restored this Post from 'drafts' - which were buried below my stack of Posts, not immediately visible on the right of the screen - and thus hard to locate. Thanks so much to you both for your kind help. With regards from Antoni

Publicado por milewski hace casi 2 años

Glad to hear it! Is this it?

Publicado por ludwig_muller hace casi 2 años

@ludwig_muller Yes, it is...

Publicado por milewski hace casi 2 años
Publicado por milewski hace casi 2 años

Falco rupicolus (https://www.inaturalist.org/taxa/472764-Falco-rupicolus) eats mainly animals other than vertebrates.

Publicado por milewski hace casi 2 años
Publicado por milewski hace casi 2 años

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