White-winged Black Tern/s at Coopers Lagoon, Canterbury

[tom.b]

Hi All,
I've put a few photos up with the ebird checklist from yesterday's visit (https://ebird.org/atlasnz/checklist/S130725258). I can confirm from photos a minimum of 5 distinct individual WWBTs.

Here is a map of where I saw them (in red) if anyone is keen to go for a look, and its slightly easier-going walking up the fenceline (in green). 6-7pm seems to be a good time for them to be out feeding and for those of you with more photographic skill than me you'll have the evening sun behind you too.
Cheers,
Tom

[Michael Szabo]

Here's a photo of one gaining breeding plumage taken by Imogen Warren at the Manawatu River Estuary in April 2021:
https://nzbirdsonline.org.nz/sites/all/ ... -22-53.jpg

[andrewcrossland]

These notes on moult timings might be interesting to compare with birds here in NZ. I made these notes over a 4 month period in 1997 while closely monitoring hundreds of White-winged Black Terns in Sumatra over the northward migration period. They may moult a little earlier than vagrant birds reaching here because they have less distance to fly back to the breeding grounds, but let's see....

28 Feb - birds all in winter plumage. very few showing any colour. 400-500 birds in stable pop.

3 Mar - some beginning to moult into BP, the most advanced moult stage being in <1/2 BP

11 Mar - wide assortment of plumages from full winter still to a > 1/2 BP

17 Mar - wide assortment of plumages

23 Mar - most birds showing black under-wings, white upper wings, but body feathers still white

25 Mar - appearance of first birds in "dalmatian" plumage - black splots on body

31 Mar - many in dalmatian plumage (also first big influxes of assumed Australian waders on passage - Red Knots, Black-tailed Godwits & Terek Sandpipers, mxing with waders that have stayed over non-breeding period - Asian Dowitcher, Eurasian Curlew, Common Redshank, etc)

A more recent pic shows the dalmatian plumage well....

WWbl Tern dalmatian plumage.JPG (38.33 KiB) Viewed 425 times

2 April - WW Bl Terns in 1/3 - 2/3 BP but none with fully black bodies yet (c.f. Whiskered Terns which are all in BP).

14 April - Big influx, doubling of numbers Majority now have fully black bodies (full BP), with remainder in "dalmatian" plumage. (Now the dominant species with c.1000 present while flocks of adult Whiskered Terns, Little Terns, & Gull-billed Terns have almost all departed, leaving mainly birds in imm/juv plumage)

17 April - Huge influx with thousands present - not just in coastal habitats, but spread wee well inland (up to 15km) over ricefields and fish ponds.

19 April and 22 April - Several groups observed on active northward migration across Straits of Malacca moving towards Malaysian coast.

23 April - Most of the big influx has moved through and migrated, Most remaining birds in full BP

24 April (200+ birds) population declining, big drop in numbers . All whiskered terns and most Little Terns now gone.

4 May - small numbers remain, mostly still adults in BP, small nos of juv/imms.

12 May (<100 birds). Almost all juv/imms. Very few adults remain.

[Michael Szabo]

Yes, it's interesting to see those Sumatra dates for comparison. I looked up the dates for NZ in CSN (1980-1999) and found only one year in which there was an influx of more than 10 WWBTs which was at Cooper's Lagoon in 1995 as follows:
10 or 11 in non-breeding plumage on 2/1
7 on 24/2
14 on 12/2
13 on 9/4
3 on 28/5 with 2 assuming breeding plumage

When searching the Birds New Zealand publications archive there are some variations in case sensitivity, so I had to try both upper case and lower case versions of the first letters of 'Classified Summarised Notes': https://www.birdsnz.org.nz/publications/

There were also some interesting details of WWBT plumages in coastal Canterbury as follows:
2 on 21/2/82 at Spider lagoon (2 in non-breeding plumage)
2 on 27/8/83 at Spider lagoon (1 immature, 1 in breeding plumage)
3 on 18/9/83 at Spider lagoon (2 moulting out of breeding plumage, 1 in winter plumage)
1 on 23/9/88 at Kaitorete spit (moulting into eclipse with traces of black on underside)
1 on 18/11/88 at Kaitorete spit (in mottled plumage)
2 on 16/2/89 at Cooper’s lagoon (1 in breeding plumage)
2 on 17/2/92 at Cooper’s lagoon (in eclipse plumage)
1 on 19/6/93 at Kaitorete spit (in breeding plumage)
4 on 25/6/93 at Kaitorete spit (3 in winter plumage, 1 moulting in or out of breeding plumage)

This all highlights the usefulness of birders using eBird and taking good quality photos of WWBTs to document plumage changes over time at the same site or in the same locality - an example of what Peter Frost has called 'jigsaw ornithology'.

[Paul Sagar]

Thanks for digging out those CSN records Michael. They prompted me to dust off the 6 x 4 inch card index files that I used to compile my records from my notebooks before getting my 1st desk-top PC. In there I found a few extra WWBT records that I hadn't submitted to CSN. These are:

1 on 23/9/78 at Spider Lagoon (non-breeding plumage)
1 on 23/12/78 at Spider Lagoon (in eclipse plumage)
1 on 23/9/79 at Spider Lagoon (in eclipse plumage)
1 on 3/5/81 at Opihi Rivermouth (breeding plumage)
2 on 25/4/82 at Opihi Rivermouth (both in eclipse plumage)
6 on 19/2/83 at Spider Lagoon (all in eclipse plumage)
2 on 27/8/83 at Spider Lagoon (1 in full breeding plumage, other bird a ?juvenile)

I recorded details of plumages on the 6 x 4 cards.

If I remember correctly the likelihood of seeing WWBT was the reason that Spider Lagoon was included in the National Wader Counts (which started in Nov 1983), even though few migratory waders occur there.

[Michael Szabo]

Thanks Paul, it's interesting that you saw one in breeding plumage on 3/5/81 at Opihi Rivermouth. I've previously seen northern hemisphere WWBTs in breeding plumage in May in Hungary and Romania, so hopefully at least some of the birds currently in NZ will stick around long enough to be seen developing their breeding plumage or even in full breeding plumage.

Spider lagoon and Opihi Rivermouth must be worth a visit to check for WWBTs at this time of year too if any birders live nearby or are passing through.

[wazzagonewild]

I visited both Spider lagoon and Opihi Rivermouth on my way home from the MacKenzie Basin this evening. Didn't have the gear to get close to the roosting terns at Opihi Rivermouth, so worth checking out for anyone with a 4WD.

Highlights were a single black-fronted dotterel at each location, and a kotuku (great egret) at the Opihi Rivermouth.

[Jan]

Hi Paul, I think there's a record of breeding at the Opihi back then, so maybe some birds were in Srn BP? It's only fairly recently that breeding has been occuring up the braided rivers, so plumages will be different nowadays, is that correct?

[Paul Sagar]

Hi Jan,

Yes, Ray Pierce found a pair nesting at the Opihi Rivermouth in 1973-74. There are earlier NZ-breeding records from the Waihopai River (Marlborough) in 1868 and Edgar Stead reported them breeding on the Rakaia in the early 1900s, so breeding plumage will have been different for a while.

[Michael Szabo]

According to Ray Pierce's 1974 paper "PRESUMED ATTEMPTED BREEDING OF THE WHITE-WINGED BLACK TERN IN NEW ZEALAND" published in Notornis, the two breeding birds had lost their breeding plumage by 18th March:

"The adult terns (Fig. 1) had full breeding dress, a smart pattern
of black, grey and white, in December and on 13 January (cf. Witherby
et al., 1941: 9-11, pl. 126). By 6 February the forehead and much
of the crown (more so in one bird) was an off-white. The underparts
were irregularly mottled with an area of white approximately equal
to that in black. Smaller patches of white occurred on the mantle.
On 21 February the head was white except for some grey on the
crown and black about and especially behind the eye. The mantle
was pale grey and the underparts all white except for a trace of
black on the breast. On 18 March neither adult could be distinguished
with any certainty from the non-breeding birds (see also figures in
Cramp 1970: 1040-1041)."

See p133: https://www.birdsnz.org.nz/wp-content/u ... s_21_2.pdf