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

@hillsflora @george_seagull @lifeisamazing @jeremygilmore @tonyrebelo

The silvereye (Zosterops lateralis, https://www.youtube.com/watch?v=HHta3iKOiR0 and https://www.inaturalist.org/taxa/202505-Zosterops-lateralis) is widespread in the southwestern part of Western Australia.

The subspecies Zosterops lateralis chloronotus (https://en.wikipedia.org/wiki/Western_silvereye) occurs in the Perth metropolitan area (https://www.inaturalist.org/observations?place_id=19379&subview=map&taxon_id=202505), where I have lived for many years.

My consistent experience in my leafy inner-city suburb, from year to year, has been - based mainly on auditory clues - that the silvereye is only noticeable over a brief period, within the autumn.

A particular pattern has been clear to me for decades, and up to the present:
Over a month or two in autumn, I notice the sibilant contact-call of the silvereye in my garden and hereabouts.

By contrast, at other times of the year I neither see nor hear the species. The main indication of its presence in spring has been peck-marks in the ripe fruits of loquat (Eriobotrya japonica, https://www.inaturalist.org/taxa/76949-Eriobotrya-japonica).

This has seemed to confirm a seasonal movement, in which the species moves gregariously through the suburbs - presumably northwards - about the time of the autumn equinox. Zosterops l. chloronotus tends to spend winter in the subtropical coastal region of Western Australia, which is semi-arid.

In and around my suburb, my impression of the silvereye is as the most seasonal of the passerines in the avifauna.

Presumably the species remains present in small numbers through winter, and returns in relatively large numbers in spring to breed. However, it becomes audible and noticeably gregarious in autumn.

Please bear in mind that

• Simon Nevill (2008, https://www.ebay.com.au/itm/335134069071?chn=ps&_ul=AU&norover=1&mkevt=1&mkrid=705-139619-5960-0&mkcid=2&mkscid=101&itemid=335134069071&targetid=1278430613456&device=c&mktype=pla&googleloc=9112576&poi=&campaignid=19649531412&mkgroupid=146789074798&rlsatarget=pla-1278430613456&abcId=9305371&merchantid=7364522&gad_source=1&gclid=Cj0KCQjwwYSwBhDcARIsAOyL0fj84V8Amv4arExKmxibHLRJN8UFWzJxM_0M1hf0Q0m33yivQHyxyOcaAvm2EALw_wcB) has stated that there tends to be a northwards movement of the silvereye in southwestern Australia, after the summer;
• the vocalisation I recognise is merely the contact-call;
• migrations northwards in autumn are well-known in eastern Australia; and
• I have never knowingly heard the song ( https://www.google.com.au/search?q=Silvereye+call+audio&sca_esv=82c0c058482216c1&sxsrf=ACQVn0_G2CtHW12KuncPFmobfGn6mGnlMg%3A1710742005946&source=hp&ei=9dn3ZaPoNYmfseMPudCKsAQ&iflsig=ANes7DEAAAAAZffoBQrMhLoUspoVVT9bxocquuv6p_KI&ved=0ahUKEwjjtsDMkv2EAxWJT2wGHTmoAkYQ4dUDCBc&uact=5&oq=Silvereye+call+audio&gs_lp=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&sclient=gws-wiz#vhid=TcEBFkbA0rHZpM&vssid=videos-40363bc1 and https://www.google.com.au/search?q=Silvereye+call+audio&sca_esv=82c0c058482216c1&sxsrf=ACQVn0_G2CtHW12KuncPFmobfGn6mGnlMg%3A1710742005946&source=hp&ei=9dn3ZaPoNYmfseMPudCKsAQ&iflsig=ANes7DEAAAAAZffoBQrMhLoUspoVVT9bxocquuv6p_KI&ved=0ahUKEwjjtsDMkv2EAxWJT2wGHTmoAkYQ4dUDCBc&uact=5&oq=Silvereye+call+audio&gs_lp=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&sclient=gws-wiz#vhid=CAB29XWMX-FVmM&vssid=videos-3efb24bf) of the silvereye hereabouts, suggesting that the species has never bred in or near my garden.

My observations over the years have, thus, been in line with a known pattern.

However, in autumn of 2024, there has been a clear difference: the seasonal prominence of the silvereye has been both accentuated and prolonged.

In 2024, the silvereye first became audible in the first half of March. I then heard and saw it in my neighbourhood on nearly a daily basis for 3 months. This indicated a considerable delay in what is usually merely a transitional pattern.

During the period 10 March-16 June 2024, the silvereye in my neighbourhood

• remained audible on a daily basis, and
• was by far the most abundant and gregarious passerine in the avifauna.

What has been unusual in this context is that

• last summer was extremely warm and dry (https://business.weatherzone.com.au/climate/second-hottest-summer-days-on-record-in-perth/ and https://www.abc.net.au/news/2024-03-09/wa-summer-weather-wrap-autumn-outlook/103541460), and
• this summer-like weather pattern has continued for an exceptionally long time through autumn (https://www.theguardian.com/australia-news/2024/mar/01/australia-sweats-through-third-hottest-summer-on-record-with-hot-and-dry-autumn-predicted and https://www.uwa.edu.au/news/article/2024/april/the-big-dry-forests-and-shrublands-are-dying-in-parched-western-australia).

For the first time in my experience, there has been noticeable mortality of Viburnum tinus (https://www.inaturalist.org/taxa/82666-Viburnum-tinus). This is a common - and usually horticulturally undemanding - hedge-plant in the Perth metropolitan area. The apparent cause is exceptional heat and drought.

A little rain fell on 30 April 2024. However, this was - remarkably - followed by several more weeks of unseasonably dry, warm weather. On 21 May 2024, the silvereye remained as noticeable as it had been in March of this year. From 22-26 May 2024, the species seemed to wane in numbers, but from 27 May-1 June 2024 it seemed abundant again.

As at 16 June 2024, the silvereye is still gregarious and audible in my garden, as it has been during the autumn.

I infer that the northward movement of the silvereye, from Perth, resumed only during winter, in 2024.

In summary:

• The abundance of the silvereye in Perth this autumn, and the duration of its presence (3 months), have been remarkable.
• This has been correlated with the exceptionally warm and dry weather throughout southwestern Western Australia.

Also see https://www.inaturalist.org/posts/94948-ecological-differences-between-lookalike-species-of-zosterops-in-southwestern-australia-and-southwestern-southern-africa#

Julkaistu maaliskuu 18, 2024 05:04 AP. käyttäjältä milewski