Differences between Perth (Western Australia) and Cape Town (South Africa) in suburban avifaunas, part 1: black-and-white colouration

@tonyrebelo @jeremygilmore @ludwig_muller @adamwelz

Please see https://www.birdsandblooms.com/birding/bird-photography/black-and-white-birds/

INTRODUCTION

The metropolitan areas of Perth (https://en.wikipedia.org/wiki/Perth_metropolitan_region) and Cape Town (https://en.wikipedia.org/wiki/Cape_Town) are comparable for various reasons, including

  • coastal location,
  • mesic mediterranean-type climates,
  • mainly sandy substrates, and
  • extensive suburbia.

In both cases,

  • the suburban avifaunas are mainly indigenous at a continental scale,
  • there have been significant invasions/introductions of bird spp. indigenous to other regions on the same continents/subcontinents (marked with an asterisk * below), and
  • a few spp. have been introduced from other continents.

AIMS

In this Post, I compare those elements of the suburban avifaunas that have black-and-white overall colouration.

METHODS

In both cases, I have excluded all aquatic birds, whether marine or freshwater. The study spp. are those seen in one's garden and while walking around the suburbs.

RESULTS for PERTH

Black-and-white:

Mainly black-and-white but also featuring grey:

Lacking black but overall strikingly white:

RESULTS for CAPE TOWN

Black-and-white:

Mainly black-and-white but also featuring grey:

The incidence of black-and-white birds in the metropolitan area of Perth exceeds than in Cape Town, according to a combination of

  • phylogenetic diversity,
  • densities of populations, and
  • body size (remarkably large in most spp. in Perth, but remarkably small in Rhipidura leucophrys).

Furthermore, many of the study spp. (other than Threskiornithidae) in Perth vocalise extremely loudly. The calls are

There is a species of Corvus in both locations. However, that in Perth is far more abundant than - and as large-bodied as (https://www.perplexity.ai/search/What-is-the-zFV0nu9SSLmUzx3sFDcDPw) - that in Cape Town.

Additional in Perth is an abundant rook-like, large passerine, belonging to an unrelated family (Artamidae, https://en.wikipedia.org/wiki/Cracticinae). I refer to Gymnorhina tibicen, typical of suburban lawns.

A superspecies of Threskiornis is represented in both metropolitan areas. However, the Australian representative has recently become common in suburban parks, ranging from these into suburban streets. The South African representative - possibly because parks are limited in Cape Town - remains more strictly tied to large rubbish dumps and metropolitan wetlands.

The species in Perth is somewhat larger-bodied than that in Cape Town (https://www.perplexity.ai/search/Which-of-the-IyJ.4bIPTQ6RVCCcAzexpA).

An additional congener has recently invaded Perth spontaneously, foraging mainly in suburban parks (as opposed to depending partly on refuse as in the case of T. molucca). This makes Threskiornis exceptional in contain two coexisting, black-and-white spp. within a single metropolitan area.

A hook-billed cracticid in Perth, weighing about 90 grams, is the approximate ecological counterpart of a laniid (about 40 grams) in Cape Town. The Australian species is the larger-bodied of the two, a caveat being that it is partly grey.

DISCUSSION

The small passerine Rhipidura leucophrys (20 grams) is currently common throughout the suburbs of Perth. It seems to be the only bird species on Earth, weighing less than 25 grams, with an unambivalently bold pattern of exclusively black-and-white plumage.

Rhipidura leucophrys thus has no counterpart in Cape Town, even if one considers the relatively uncommon Melaenornis silens.

Black-and-white, and all-black, are unusual colourations for small birds. Among the few examples worldwide are:

A possible explanation for the commonness of conspicuously marked - and correspondingly noisy - large birds in Perth relates to the relatively light regime of predation on the 'island continent'.

And, indeed, T. molucca, C. coronoides, and G. tibicen, and particularly G. cyanoleuca, and R. leucophrys, are remarkably habituated to human proximity, to degree unknown for any indigenous bird in Cape Town. They allow close approach in the case of the first three spp., and actually approach gardeners to < 1 meter in the case of the last two spp.

Furthermore, G. tibicen actually attacks humans during its breeding season (https://www.science.org.au/curious/earth-environment/how-survive-magpie-swooping-season and https://neoskosmos.com/en/2019/10/02/dialogue/opinion/why-are-dangerous-australian-magpies-so-different-to-their-docile-european-counterparts/ and https://www.qld.gov.au/environment/plants-animals/animals/living-with/magpies/swooping and https://blog.nationalparks.nsw.gov.au/how-to-avoid-being-swooped-by-a-magpie/ and https://www.magpiealert.com/ and https://en.wikipedia.org/wiki/Animal_attacks_in_Australia).

In this context it is worth considering the mainly black colouration of Accipiter melanoleucus in Cape Town. This raptor (adult female body mass 0.75-1 kg) preys typically on columbids, which it hunts by stealth. Its colouration functions for concealment rather than advertisement, because it hides in the crowns of trees, and any white bib is in a relatively hidden position anatomically.

Posted on May 07, 2024 12:18 AM by milewski milewski

Comments

Posted by milewski 2 months ago

The following contains information on body masses of bird occurring in and near Cape Town:

https://consbio.org/wp-content/uploads/2022/05/Fynbos_publication.Phoebe.pdf

Posted by milewski 2 months ago
Posted by milewski 2 months ago
Posted by milewski 2 months ago

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