June 08, 2024

June 07, 2024

June 05, 2024

A new interpretation of the evolutionary and ecological strategy of whiteyes/silvereyes (Zosterops), part 3: encephalisation (braininess)

@tonyrebelo @jeremygilmore @ludwig_muller @jwidness @zarek @hirons @ldacosta @lukedowney @moxcalvitiumtorgos @carasylvia @rion_c @nwatinyoka @shauns @baldcoot @karoopixie @gareth_bain @justinponder2505 @christiaan_viljoen @bushbandit

...continued from https://www.inaturalist.org/journal/milewski/95204-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-silvereyes-zosterops-part-2-a-nectarivorous-species-z-chloronothos-as-an-exception-proving-a-rule#


Zosterops is among the more encephalised (https://dictionary.apa.org/encephalization) of birds.

This is based on brain mass relative to body mass (corrected allometrically, https://en.wikipedia.org/wiki/Allometry).

This braininess may help to explain how Zosterops has adapted to various biomes, on many islands as well as on mainlands, with minimal morphological modification.

Adaptation in this genus seems to be mainly a matter of behavioural versatility, i.e. via 'software' rather than 'hardware'.

The cognitive capacity of Zosterops may be evident, for example, in

  • vocal mimicry,
  • discrimination among subspecies, allowing these coexist for part of the year without loss of subspecific integrity, and
  • ability to stitch a cup-shaped nest between adjacent flimsy stems in the crowns of various trees, despite various stem-configurations according to the type of tree.

There is a correlation between vocal mimicry and encephalisation (https://cdnsciencepub.com/doi/10.1139/z03-190 and https://www.perplexity.ai/search/Is-there-a-8dJObx_JS0CR6jhS3.Dl4g and https://www.animalecologylab.org/the-mimics-among-us.html).

Birds capable of mimicking the calls of other birds tend to be relatively brainy.

A noteworthy phenomenon, in Zosterops lateralis (https://www.inaturalist.org/taxa/202505-Zosterops-lateralis) in southeastern mainland Australia, is that several subspecies overlap in geographical distribution.

In the normal concept of subspeciation, geographical separation is necessary to maintain the distinctiveness of subspp. In Z. lateralis, the nomadic/migratory movements in the non-breeding season mix several subspp. (https://avithera.blogspot.com/2014/04/silvereyes.html). However, this has not compromised the subspecific distinctions.

This ability to coexist without interbreeding seems to reflect cognitive capacity, possibly extending to 'culture'.

All of the above raise the question:
How brainy is Zosterops, compared to other like-size, small birds?


In this Post, I compare Zosterops with other birds in terms of encephalisation, i.e. braininess.


My reference for body mass and brain mass in various spp. of birds is the data-set compiled by Andrew N Iwaniuk (https://www.ulethbridge.ca/artsci/neuroscience/dr-andrew-iwaniuk). The data refer to adults of both sexes, in all spp.


I searched the entire data-set for bird spp. with body mass similar to that of Zosterops, viz. about 10.4 g. I then compared the brain masses on the basis of body masses similar to that in Zosterops.


The mean data for Zosterops are

  • body mass 10.2 g, brain mass 0.54 g in Zosterops japonicus (n=10), and
  • body mass 10.6 g, brain mass 0.47 g in Zosterops lateralis.

This shows that Zosterops has brain mass 0.50 g, at body mass 10.4 g.

Let us now compare this brain mass with those of various other birds with similar body masses.

Families are in alphabetical order.

Apodidae (https://en.wikipedia.org/wiki/Swift_(bird)) :

I found two spp., in two genera, with body masses 9.9-13.6 g. Brain masses were 0.28-0.30 g, indicating that Zosterops clearly exceeds apodids in braininess.

Apodids attain brain mass of 0.5 g only at body masses > 25 g, e.g. in Chaetura pelagica (https://www.inaturalist.org/taxa/6571-Chaetura-pelagica), which has brain mass 0.46 g at body mass 23.6 g. (n=8).

Certhiidae (https://en.wikipedia.org/wiki/Treecreeper) :

I found four spp., in four genera, with body masses 9.8-11.0 g. Brain masses were 0.51-0.53 g, indicating that certhiids exceed Zosterops in braininess.

Cisticolidae (https://en.wikipedia.org/wiki/Cisticolidae) :

I found two spp., in one genus, with body masses 10.0-10.3 g. Brain masses were 0.43-0.51 g, indicating that Zosterops slightly exceeds cisticolids in braininess.

Fringillidae (https://en.wikipedia.org/wiki/Finch) :

I found 15 spp., in 14 genera, with mean body masses 8.9-12.0 g. Brain masses were somewhat variable, with particular braininess evident in Melopyrrha nigra (https://www.inaturalist.org/taxa/10266-Melopyrrha-nigra), which had brain mass 0.84 g at body mass 10.9 g (n=7).

Overall, the data indicate that Zosterops resembles fringillids in braininess.

Hirundinidae (https://en.wikipedia.org/wiki/Swallow) :

I found two spp., in two genera, with mean body masses 9.7-11.2 g. Brain masses were 0.36-0.43 g, indicating that Zosterops exceeds hirundinids in braininess.

Lybiidae (https://en.wikipedia.org/wiki/Lybiidae) :

I found only one comparable species, with body mass 15.5 g and brain mass 0.44 g, indicating that Zosterops exceeds lybiids in braininess.

Maluridae (https://en.wikipedia.org/wiki/Australasian_wren) :

I found three spp., in one genus, with mean body masses 9.8-11.4 g. Brain masses were, on average, about 0.48 g, indicating that Zosterops slightly exceeds malurids in braininess.

Melanocharitidae (https://en.wikipedia.org/wiki/Melanocharitidae) :

The data indicate that Zosterops exceeds melanocharitids in braininess.

Meliphagidae (https://en.wikipedia.org/wiki/Honeyeater) :

I found nine spp., in seven genera, with mean body masses 7.8-11.9 g in Myzomela, and 10.3-11.4 g in other genera. Brain masses were somewhat variable. However, they indicate that, overall, Zosterops exceeds meliphagids in braininess.

Monarchidae (https://en.wikipedia.org/wiki/Monarch_flycatcher) :

I found two spp., in two genera, with mean body masses 10.2-11.0 g. Brain masses were 0.52-0.59 g, indicating that monarchids exceed Zosterops in braininess.

Muscicapidae (https://en.wikipedia.org/wiki/Old_World_flycatcher) :

I found five spp., in five genera, with mean body masses 7.5-15.4 g. Brain masses were 0.31-0.6- g. One species, viz Ficedula albicollis (https://www.inaturalist.org/taxa/13133-Ficedula-albicollis, n=10), closely resembled Zosterops in mean body mass (10.3 g), and had brain mass 0.45 g.

Overall, these data indicate that Zosterops exceeds muscicapids in braininess.

Nectariniidae (https://en.wikipedia.org/wiki/Sunbird) :

I found two spp., in two genera, with mean body masses 8.9-11.7 g. Brain masses were, on average, about 0.45 g, indicating that Zosterops exceeds nectariniids in braininess.

Pardalotidae (https://en.wikipedia.org/wiki/Pardalote) :

I found three spp., in two genera, with mean body masses 9.2-11.6 g. Brain masses were, on average, about 0.45 g, indicating that Zosterops exceeds pardalotids in braininess.

Paridae (https://en.wikipedia.org/wiki/Tit_(bird)) :

I found three spp., in one genus, with mean body masses 10.2-11.3 g. Brain masses were, on average, about 0.65 g, indicating that parids are brainier than Zosterops.

Passeridae sensu lato, including Estrildidae (https://en.wikipedia.org/wiki/Old_World_sparrow and https://en.wikipedia.org/wiki/Estrildidae) :

I found seven spp., in six genera, with mean body masses 9.2-10.9 g. Brain masses were, on average, about 0.45 g, indicating that Zosterops exceeds passerids in braininess.

Petroicidae (https://en.wikipedia.org/wiki/Australasian_robin) :

I found three spp., in two genera, with mean body masses 9.6-11.4 g. Brain masses were, on average, about 0.52 g, indicating that petroicids are slightly brainier than Zosterops.

Picidae (https://en.wikipedia.org/wiki/Woodpecker) :

I found two spp., in two genera, with mean body masses 8.1-11.0 g. Brain mass was 0.58-0.60 g, indicating that picids exceed Zosterops in braininess.

Rhipiduridae (https://en.wikipedia.org/wiki/Rhipiduridae) :

I found one species, with body mass 10.2 g (n=7). Brain mass was 0.36 g, tentatively indicating that Zosterops exceeds rhipidurids in braininess.

Sittidae (https://en.wikipedia.org/wiki/Nuthatch) :

There is only one genus in this family, represented in the data-set by Sitta canadensis (body mass 10.5 g, brain mass 0.57 g, n=6). This indicates that sittids exceed Zosterops in braininess.

Sylviidae (https://en.wikipedia.org/wiki/Sylviidae) :

I found only one species (n=7), with mean body mass 10.8 g. Brain mass was 0.45 g, tentatively indicating that Zosterops exceeds sylviids in braininess.

Thamnophilidae (https://en.wikipedia.org/wiki/Antbird) :

I found four spp., in four genera, with body masses 9.3-11.2 g. Brain masses (means) were 0.45-0.7 g, indicating that thamnophilids are slightly brainier than Zosterops.

Trochilidae (https://en.wikipedia.org/wiki/Hummingbird) :

I found only one species large-bodied enough to be comparable, with mean body mass 10.2 g. Brain mass was 0.32 g, indicating that Zosterops exceeds trochilids in braininess.

Tyrannidae (https://en.wikipedia.org/wiki/Tyrant_flycatcher) :

I found eight spp., in eight genera, with mean body masses 8.6-11.9 g. Brain masses were, on average, about 0.37 g, for six of the spp., indicating that Zosterops exceeds tyrannids in braininess.

The brain mass of Zosterops (about 0.5 g) is attained in these tyrannids only when body mass reaches about 14 g, which is >3.5 g heavier than Zosterops.

However, apparently brainier than other tyrannids are two spp., viz.


Brain mass, relative to body mass, varies up to 2.5-fold in small-bodied birds about the size of Zosterops. This can be seen in the following three carefully chosen examples:

The percentage value for Zosterops, viz. 4.8%, falls approximately in the middle of the above range (2.8-7.7%) of values.

However, Zosterops is somewhat brainier than most birds that are comparable on a basis of matched body mass but different familial affinity.

The following summarises the ranking of Zosterops in braininess, relative to like-size, small birds, family by family.

Zosterops is less brainy than

  • monarchids,
  • parids,
  • picids, and
  • sittids.

Zosterops is somewhat/slightly less brainy than

  • petroicids,
  • thamnophilids, and
  • one or two genera of tyrannids.

Zosterops is similar in braininess to

  • fringillids.

Zosterops is somewhat/slightly brainier than

  • cisticolids, and
  • malurids.

Zosterops is brainier than

  • certhiids,
  • hirundinids,
  • lybiids,
  • melanocharitids,
  • meliphagids,
  • muscicapids,
  • nectariniids,
  • pardalotids,
  • passerids,
  • rhipidurids,
  • sylviids,
  • trochilids, and
  • most tyrannids.

Zosterops seems much brainier than

  • apodids.

This means that Zosterops is brainier than like-size birds in most avian families.

However, Zosterops is less brainy than like-size birds in perhaps seven families, of which parids (tits) are the most renowned for their cognitive capacity (https://lup.lub.lu.se/search/files/31008096/e_spik_utku.pdf).

Posted on June 05, 2024 03:28 AM by milewski milewski | 3 comments | Leave a comment

June 02, 2024

Subtle differences among reedbucks (Redunca spp.) in size of tail and colouration on the hindquarters

The proportional size of the tail varies, among the three spp. of Redunca, in the order fulvorufula > arundinum > redunca.

The following show that the tail is proportionately larger in Redunca arundinum than in Redunca redunca:

The following shows how small the tail can be in Redunca redunca.

The following shows Redunca arundinum for comparison:

In the latter photo, note the bare, dark skin at the junction of flank and knee, a feature shared (approximately) with Aepyceros melampus.

Redunca arundinum:





Redunca redunca:





The following (https://www.inaturalist.org/observations/109676221) is one if the few photos showing clearly the colouration on the buttocks, in Redunca arundinum.

The following (https://www.inaturalist.org/observations/104986782) suggests that the pattern is different in Redunca redunca, with negligible whitish on the buttocks.

Posted on June 02, 2024 10:59 PM by milewski milewski | 2 comments | Leave a comment

Contrary to field guide-books, reedbucks (Redunca spp.) do not flag the tail in alarm, part 2: further illustrations

...continued from https://www.inaturalist.org/journal/milewski/39738-contrary-to-field-guide-books-reedbucks-redunca-spp-do-not-flag-the-tail-in-alarm-part-1#

Since I wrote part 1, many further photos have emerged of Redunca spp., further illustrating the fact that, in general, reedbucks do not raise the tail in anti-predator alarm.

At the same time, many photos show caudal flagging in social contexts.

Some photos are ambivalent, deserving closer scrutiny.



last photo in https://www.inaturalist.org/observations/148182517



Showing tail socially
(showing caudal flag in social, not anti-predator, context):




Second and third photos in https://www.inaturalist.org/observations/210385838

Showing tail socially:




The following deserves close scrutiny: https://www.inaturalist.org/observations/202324823


Additional photos showing that Redunca fulvorufula does not raise its tail when fleeing:
third photo in https://www.inaturalist.org/observations/194955710

Posted on June 02, 2024 05:08 PM by milewski milewski | 2 comments | Leave a comment

A new interpretation of the evolutionary and ecological strategy of whiteyes/silvereyes (Zosterops), part 2: a nectarivorous species (Z. chloronothos) as an exception proving a rule

...continued from https://www.inaturalist.org/journal/milewski/95051-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-and-silvereyes-zosterops-part-1#

In general, the genus Zosterops has combined great speciation with minimal adaptive radiation.

This is explained partly by the facts that

  • Zosterops is capable of inhabiting islands as small as one square kilometer, and
  • most of the species are restricted to islands of various sizes, up to the size of Madagascar, New Guinea, and mainland Australia.

In other words, speciation in Zosterops has been nominal, with minimal modification of a morphological kind.

In this Post, I explore one example - on the island of Mauritius in the Indian Ocean - in which two sympatric spp. of Zosterops have separated in terms of diet.

This example is 'an exception that proves a rule', in the sense that

  • there is a clear specialisation in nectar in one of the spp., including a significant lengthening of the beak, but
  • the adaptation has been more behavioural than morphological, i.e. it reflects a change in 'software' rather than 'hardware'.




Zosterops chloronothos (https://earthlife.net/mauritius-olive-white-eyes/Mauritius), which is naturally restricted to Mauritius, has

The diet is mainly nectar and flying insects. Fleshy fruits and gleaned insects, normally part of the diets of Zosterops, are hardly taken by Z. chloronothos.

Zosterops chloronothos is not merely a 'cheat' in the sense of taking nectar without pollinating the plants. Unusually for its genus, it also collects pollen on the forehead.

Plant spp. possibly pollinated by Z. chloronothos (https://www.perplexity.ai/search/Which-plants-indigenous-2OJN2oIbQ2eGSNt0negoIQ) include



I interpret the nectarivory of Z. chloronothos as follows.

On one hand, it is true that

  • Z. chloronothos deviates from the norm in its emphasis on exudates (nectar and sap), to the near-exclusion of other dietary components normal in its genus, viz.
  • fleshy fruit-pulp, and
  • insects, such as Homoptera (https://en.wikipedia.org/wiki/Homoptera), gleaned from plants.

On the other hand, it is also true that

What this means is that the deviation from the norm in Z. chloronothos is open to interpretation. It is simultaneously true that here we have an island-effect, in which Zosterops has 'filled in for' the paucity if true nectarivores - particularly Nectariniidae (https://en.wikipedia.org/wiki/Sunbird) - in the avifauna of Mauritius.



Delphacidae occur on Oceanic islands and produce honeydew

to be continued in https://www.inaturalist.org/journal/milewski/95329-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-silvereyes-zosterops-part-3-encephalisation-braininess#...

Posted on June 02, 2024 05:21 AM by milewski milewski | 8 comments | Leave a comment

May 31, 2024

Body size on mainlands versus islands, in whiteyes and silvereyes (Zosteropidae: Zosterops)

@thebeachcomber @lukedowney @kokhuitan @hedgehog111 @lloyd_esler @rion_c @tonyrebelo @jeremygilmore


The genus Zosterops, in the family Zosteropidae, is remarkably widespread in Africa, Asia, Australasia, the Indian Ocean, and the western Pacific (https://www.inaturalist.org/observations?taxon_id=17439).

Furthermore, the many spp. of Zosterops are remarkably consistent in their generalised body-proportions and diminutive body size.

What this means is that, although this genus qualifies as remarkably speciose (https://www.collinsdictionary.com/submission/17774/speciose#:~:text=Of%20a%20taxon%20or%20other,many%20species%3B%20species%2Drich.), it does not seem to have undergone much adaptive radiation (https://en.wikipedia.org/wiki/Adaptive_radiation).


A well-known biogeographical pattern is that, among small birds and small mammals, the forms on islands tend to be relatively large-bodied (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691042/ and https://www.jstor.org/stable/3448886 and https://nsojournals.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1600-048X.2012.05820.x and https://www.perplexity.ai/search/Various-passerine-birds-8OD79qKESu..NPBfwAcnrg).

This raises the question:
Do species/subspecies of Zosterops on islands tend to be larger-bodied than those on mainlands?



Zosterops virens and Zosterops pallidus are restricted to southern Africa. Their values for body length and body mass are, respectively:

  • about 12 cm and 8-15 g, and
  • 12-13 cm and 8-20 g.

Zosterops abyssinicus is restricted to northeastern Africa and southern Arabia. It has body length 10-12 cm (https://en.wikipedia.org/wiki/Abyssinian_white-eye).

Zosterops senegalensis is restricted to West and central Africa. It has body length about 11.5 cm and body mass 7-14 g (https://en.wikipedia.org/wiki/Northern_yellow_white-eye).


Zosterops palpebrosus has body length 8-9 cm (https://www.perplexity.ai/search/What-is-the-TubdL27WQ_CkvjY53Kzdbw). Zosterops japonicus has body length 10-12 cm, and body mass 10-13 g (https://www.perplexity.ai/search/What-are-the-1sCGnnQJSquLDTXxrGEYgw).


Zosterops lateralis occurs on both the Australian mainland and many islands of various sizes, in the western Pacific, east of the mainland (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4607525/). On the mainland, it has body length about 12 cm and body mass about 11 g (https://www.perplexity.ai/search/What-is-the-0LPFYjq7SwyQfM7xs_3Jgg).

Overall, on mainlands:
Zosterops, regardless of species, has body length about 12 cm, and body mass about 11.5 g.


Body mass in certain populations of Z. lateralis, inhabiting islands, is about 2 g more than on the Australian mainland (https://nsojournals.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1600-048X.2012.05820.x).

In New Zealand, body mass of Z. lateralis lateralis is about 13 g (https://www.birdsnz.org.nz/publications/diurnal-pattern-of-mass-in-an-urban-marlborough-population-of-silvereyes-zosterops-lateralis/ and https://nzbirdsonline.org.nz/species/silvereye and https://nzbirdsonline.org.nz/sites/all/files/ZOSLAT_FG.pdf and https://www.perplexity.ai/search/Which-species-of-3wYdn_FQQfW92M9qKJNDZA).

An extreme example is Zosterops lateralis chlorocephalus, restricted to the Capricorn-Bunker group of islands (https://en.wikipedia.org/wiki/Capricorn_and_Bunker_Group), off the Great Barrier Reef. This weighs 14-15 g, which is about 4 g heavier than conspecifics on the mainland.

Zosterops lateralis melanops, restricted to New Caledonia, has body mass about 14 g (https://www.perplexity.ai/search/Which-species-of-3wYdn_FQQfW92M9qKJNDZA).

On Lord Howe Island (https://en.wikipedia.org/wiki/Lord_Howe_Island), off eastern Australia, there are two indigenous spp. of Zosterops, viz.

Turning to spp. other than Z. lateralis, on islands:

On Norfolk Island (https://en.wikipedia.org/wiki/Norfolk_Island), two spp. occur, both of which are restricted to the island and are relatively large-bodied, viz.

In Vanuatu (https://en.wikipedia.org/wiki/Vanuatu), Zosterops flavifrons has body length 11-12 cm (https://en.wikipedia.org/wiki/Vanuatu_white-eye).

On the islands beyond the coastal shelf in Indonesia:

Sulawesi: https://www.perplexity.ai/search/What-are-the-9QxPwtDlR_yGxgVjekolvw.

Zosterops natalis, restricted to Christmas Island, has body length 12-13.5 cm and body mass about 11 g.

On Lifou island (https://en.wikipedia.org/wiki/Lifou), New Caledonia, the largest- and smallest-bodied members of genus Zosterops coexist. Body mass in Zosterops inornatus is 22 g, whereas that in Zosterops minutus is 9 g (https://www.perplexity.ai/search/Body-size-of-GfBALZ1lSpOjYyiQGLoOPQ).

Zosterops conspicillatus, restricted to the Northern Mariana islands, has body length 12 cm.

Islands between Madagascar and Africa:

Mascarene Islands (Mauritius and Reunion):


The evidence for the 'island rule' in Zosterops is ambivalent.

On one hand, several species and subspecies, occurring on islands in the western Pacific Ocean, do show enlargement in body size.

The prime example: in New Caledonia there is nominally an adaptive radiation, consisting of two sympatric spp. differing more than two-fold in body mass.

On the other hand, this effect is not apparent on islands in the Indian Ocean. On the contrary, all four spp. in the Mascarene Islands, for example, are smaller-bodied than is typical on mainlands.

Furthermore, even in the western Pacific,

Therefore, I find overall that Zosterops remains remarkable for its diminutive body size, whether on mainlands or on islands.

Its consistently small, thin beak and brush-tipped tongue may constitute an unique combination among the avian genera on Earth (https://www.inaturalist.org/journal/milewski/95051-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-and-silvereyes-zosterops#).

This may help to explain why adaptive radiation may be largely irrelevant to Zosterops, even on landmasses too remote to have been reached by other birds.

Posted on May 31, 2024 04:39 PM by milewski milewski | 4 comments | Leave a comment

May 30, 2024

May 29, 2024

A new interpretation of the evolutionary and ecological strategy of whiteyes/silvereyes (Zosterops), part 1


Zosterops spp. (whiteyes and silvereyes, https://www.inaturalist.org/observations?place_id=any&subview=map&taxon_id=17439&view=species) are odd in several ways.

They are

Crucial is the observation that Zosterops oddly combines a brush-tipped tongue with a short beak (https://www.perplexity.ai/search/Please-list-all-P5272Q3URqe3IcoI547GAg).

In this Post, I introduce the idea that the original evolutionary strategy of Zosterops was to be simultaneously

Delphacidae https://en.wikipedia.org/wiki/Delphacidae

Most small birds participating in ornithophily have long beaks (https://pubmed.ncbi.nlm.nih.gov/36062802/ and https://evolution.berkeley.edu/convergent-evolution-its-for-the-birds/). These are inefficient for gleaning homopterans.

Furthermore, aphids tend to be scarce

  • in the nutrient-poor, fire-prone ecosystems typically associated with Meliphagidae and Promeropidae, and
  • on oceanic islands.

In Australia, aphids are generally replaced by psyllids (https://en.wikipedia.org/wiki/Psyllid) and other armoured forms of sap-sucking Hemiptera (https://en.wikipedia.org/wiki/Hemiptera), predated mainly by small passerines with specialised, broad beaks (https://en.wikipedia.org/wiki/Pardalote and https://en.wikipedia.org/wiki/Weebill).

Long-beaked, nectarivorous birds do take remarkably small insects routinely, but mainly by hawking (https://en.wikipedia.org/wiki/Hawking_(birds) and https://researchportal.murdoch.edu.au/esploro/outputs/other/The-possible-ecological-significance-of-hawking/991005541828107891 and https://www.researchgate.net/publication/283793917_Ecology_of_Honeyeaters_Meliphagidae_in_Western_Australian_Eucalypt_Woodlands_I_Resource_Allocation_Among_Species_in_the_Great_Western_Woodland_During_Spring and https://www.sciencedirect.com/science/article/abs/pii/S0003347205802295).

I suggest that Zosterops has evolved essentially as a consumer of, simultaneously,

From this origin, Zosterops has been able

  • to succeed on those small islands to which the widespread mutualism between homopterans and protective ants does not extend, and
  • to adapt to a remarkably wide range of ecosystems, by means of certain 'laterally-stretched' applications of its basic nature.

The various adaptations of Zosterops have been mainly behavioral, not morphological: it has retained small body size and a consistent shape (including the beak), while being versatile in other ways. The genus has applied a single body-form to various niches, in an 'evolutionary radiation' antithetical to the classic example of modification of body-form in Darwin's finches (https://en.wikipedia.org/wiki/Darwin%27s_finches).

Given that its taste for sugars was originally oriented towards honeydew, the taking of fleshy fruit-pulp and -juice by Zosterops can be interpreted as opportunistic rather than central to the evolutionary strategy.

This in turn helps to explain why Zosterops has remained small-bodied relative to most coexisting birds that eat fleshy fruits, forgoing many fruits too large for it to swallow whole.

In particular, Zosterops varies in

  • residency (sedentary vs nomadic vs migratory), albeit never a migrant between hemispheres,
  • diet, e.g. emancipated from aphids in Australia, where it takes sugary exudates from eucalypts and Acacia (in the strict sense, https://en.wikipedia.org/wiki/Acacia) instead, and
  • mutualistic participation with a few clades of plants (e.g. Corymbia, Berzelia, ?Metrosideros) in pollination, and
  • mutualistic participation with many clades of plants in seed-dispersal.

In southwestern Western Australia, the subspecies Zosterops lateralis chloronotus (https://www.inaturalist.org/posts/91030-extreme-seasonal-incidence-of-the-silvereye-zosterops-lateralis-chloronotus-in-autumn-of-2024-in-the-perth-metropolitan-area-western-australia-in-response-to-heat-and-drought) naturally had a habitat - throughout the year and regardless of its partial latitudinal migration - virtually devoid of aphids. I refer to the situation before aphids were anthropogenically introduced to Australia, and inadvertently promoted by horticulture, agriculture, and the application of fertilisers.

Here, it has applied its brush-tipped tongue to the extrafloral nectaries of Acacia (https://www.researchgate.net/figure/Extrafloral-nectaries-EFNs-are-universal-on-the-leaves-and-phyllodes-of-SouthWest_fig16_276919754).

In Hawaii, aphids and ants - and Zosterops - were naturally absent from the indigenous biota (https://www.perplexity.ai/search/Which-genera-of-oM7eVb_fTQyunhB_CqpaRw). The extreme success of the anthropogenic introduction of Zosterops to this archipelago has probably been facilitated by the introduction of the insects and plants necessary to establish the mutualism that produces honeydew.

To what degree has Zosterops adapted to the anthropogenic introduction of aphids in Australia, by eating these insects?



to be continued in https://www.inaturalist.org/journal/milewski/95204-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-and-silvereyes-zosterops-part-2#...

Posted on May 29, 2024 03:53 PM by milewski milewski | 23 comments | Leave a comment

May 28, 2024

The former - and nearly forgotten - commonness of the ring-necked dove (Streptopelia capicola) in Cape Town, South Africa

@adamwelz @jeremygilmore @tonyrebelo

While I was a teenager, growing up in Cape Town in the 'sixties, the ring-necked dove (Streptopelia capicola, https://www.inaturalist.org/taxa/2959-Streptopelia-capicola and https://thebdi.org/2022/03/08/cape-turtle-dove-streptopelia-capicola/) was the common indigenous columbid in this metropolitan area in South Africa (https://en.wikipedia.org/wiki/Cape_Town).

At that time, the red-eyed dove (Streptopelia semitorquata, https://www.inaturalist.org/taxa/2988-Streptopelia-semitorquata) was nominally present in Cape Town. However, I was unfamiliar with it or its call.

Today, the latter species is unquestionably the common member of its genus in Cape Town, with the erstwhile commonness of the former species nearly forgotten.

Two aspects of this species-replacement, which has been natural and spontaneous albeit ultimately anthropogenic, warrant mention here.

These are

  • how rapidly indigenous birds can adapt to changes in the environment at a biogeographical scale, altering their distribution, habitat, and population-density over a period of merely a few decades, and
  • how even major avifaunal changes, in regions well-populated by naturalists and ornithologists, can come to be forgotten because they happen gradually enough that, at each stage of the process, the status quo tends to be taken for granted.

Such changes, although remarkable in hindsight, can seem so mundane that naturalists and scientists do not bother to write them down for posterity. The substitution has been obvious to me over my lifetime. However, there is a risk that the fact of it may fail to be transmitted to subsequent generations.

What is simply a matter of experience for me may come, in future, to be merely some unsubstantiated historical hypothesis.

So, for the record:

  • which readers remember a time when the call of the ring-necked dove was an everyday sound in the suburbs of Cape Town? and
  • does anyone know of any publication that has documented this switch from one congener to another?
Posted on May 28, 2024 03:58 PM by milewski milewski | 3 comments | Leave a comment

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