Mourning Warbler on Corvo: a Western Palearctic first


I had always wanted to bird Corvo, the most westerly island in the Azores, in the wake of a hurricane. On previous trips, Bob Swann and I had targeted mid-September low-pressure systems with great success, twitching the weather systems rather than birds. The traditional time to visit Corvo has always been mid- to late October.


Hurricane Lee

This autumn, Hurricane Lee's route started to look interesting from 12 September. On 16th it slammed into the southern tip of Nova Scotia having tracked all the way up the eastern seaboard during peak warbler migration season. By 18th, Bob and I were mobilising and arrived on the island on the morning of 22nd. The remnants of Lee had tracked quickly east across the Atlantic and included a massive warm-air sector, the tail end of which was deflected southwards by a low pressure just south of Iceland. Anything migrating in that tail would now be in the Azores. 

By 25th, we had found Chestnut-sided Warbler, Tennessee Warbler, American Redstart, two Black-and-white Warblers and five American Cliff Swallows. Our good friend and top bird finder, Pierre-André Crochet, soon arrived on 24th, quickly bringing his flights forward after hearing of our plans and seeing the forecast.

View of the upper Lighthouse Valley on Corvo (Peter Stronach).

On 25th, we got an early taxi together from the village and headed for Lighthouse Valley in the north of the island. As we walked to the valley from the drop-off point we stopped and briefly pished in a small gully, a Black-and-white Warbler almost immediately appeared. Then Pierre persuaded us to check the top of Lighthouse Valley, an area of comparatively little cover with just dry-stone walls, thick hydrangea hedges and patches of brambles. This area usually gets ignored in favour of the laurels and the famous junipers further down the valley.



We did more high-pitched pishing in upper Lighthouse and immediately an American warbler started calling in a nearby juniper, I uttered a clipped "yes" and pointed to the sound coming out of the tree. "It's coming, it's coming," I said as it quickly made its way through a hydrangea hedge towards us, still unseen. It was running out of hedge and the part it was in was a dead end. As it was clear it was going to emerge into the open I went for my camera, while both Pierre and Bob looked on with binoculars.

"It's a Connecticut!" exclaimed Pierre, while I tried desperately to focus on the bird. However, the numerous hydrangea twigs prevented me from locking on and after two to three seconds it turned and moved back into cover. I looked at my photos but all were blurred and it was a sinking feeling knowing the skulkiness of this species and hearing it slink back into heavy cover, potentially never to be seen again. Both Pierre and Bob were convinced it had a complete eyering, my 'take photos first, ask questions later' approach hadn't paid off this time and I just hadn't managed enough detail through the camera to contribute to the eyering debate.

The finders' first views of the bird had them thinking of Connecticut Warbler, a species with one previous Western Palearctic record – trapped and ringed on Flores on 12 October 2019 (Vincent Legrand).

It was 8.30 am. We waited and eventually the bird started calling again briefly. It called for short periods but always remained completely hidden. We decided we needed help, so Pierre went back to get phone reception and announce the news to the outside world. Meanwhile, Bob and I persevered and managed to get a couple of good field recordings of its call.



Pierre's message on the Azores Bird News WhatsApp group ensured a quick response from the other birders on the island and the Swedish birding team Jesper, Olaf and Mårten joined us almost immediately. We decided to spread out around the bramble patch and hedges and wait, the bird eventually showed in flight a couple of times and continued to call infrequently. A breakthrough came when the bird unexpectedly flew across a 5-m gap between hedges, somewhat unbelievably in the couple of seconds it took to fly across Mårten had managed to get flight shots from 40 m away! I’m used to Scandinavian birders being sharp, but this was Jedi-levels of fieldcraft. Later, he managed to catch it landing in brambles before dropping to the ground.

Finally, we had some tangible evidence of the bird's existence – photos (albeit blurred because of the movement) and recordings. The former allowed some sort of analysis of the eyering, the colour of the belly and the length of the undertail coverts. The first recording below gives a good indication of what the bird sounded like in the field with a Blackcap, Azores Chaffinch and Grey Wagtail in the background.


Arriving home that night I uploaded the calls and then checked them. I couldn't find any Connecticut calls on Xeno-Canto that matched ours, but there were Mourning calls that did match well (albeit not perfectly). We sent the photos and recordings to three North American experts. The verdict was split, with one in favour of Connecticut and two in favour of Mourning. Posting the photos and recordings on the Corvo Birders Facebook page also started discussions, with a particularly useful analysis of the calls by Alexis James.

We had good recordings, which might have proved to be enough, but we wanted to get a photo to seal the deal. This meant more time in the field in tough conditions to get that vital proof ...

First-winter Mourning Warbler has typically brighter underparts than Connecticut Warbler, with breaks along the anterior and posterior edges of the eyering (Vincent Legrand).

In the end, we spent 20 hours in the field over the four days it took to get a photo. The morning of 28th was completely calm. This was the game-changing moment, as now any slight movement of the bird was reflected by a movement of vegetation. As soon as the bird called we concentrated our effort on that area. The breakthrough came when the bird popped into a small laurel and Ole Krome shouted: "the bird is here!"

I yelled at him to get a photo, which he thankfully did as it perched on a rock for a second. The photo showed a broken eyering most noticeable in front of the eye, and yellow on the throat. It was a Mourning Warbler!  The pressure relief was immense, with big hugs and celebrations all around. It had been a real international team effort to conclude this one.

The bird continued to show well in the good weather ensuring everybody that came saw it and better photos were obtained, including some absolute stunners from Vincent Legrand.

Most initial views of the Mourning Warbler were in flight between different bramble patches and hedges (Vincent Legrand).


Lessons learnt

For anyone in the future lucky enough to stumble upon a Connecticut or Mourning Warbler in the Western Palearctic:

  • The best playback response was from a recording of its own call;
  • Both Mourning and Connecticut can show a broken eyering. However, breaks in the eyering of Connecticut (if any) are sharp and small, whereas Mourning has larger gaps, creating 'eye arcs' with a tapering of the pale colouration without a sharp definition;
  • A photo of the head of a stationary bird in profile is needed to adequately judge the eyering completeness;
  • Calls between Morning and Connecticut are different, the call we heard in the field was the one Sibley describes as a pwich in Mourning and a pwik in Connecticut. Connecticut (example call here) is short, high-pitched, squeakier and more musical. Mourning (example call here) is a lower-pitched, flatter sound.

A big thanks to all the birders on the island who helped, those experts who gave their views on the photos and recordings, and all others who contributed.

Mourning Warbler, Corvo, Corvo (Vincent Legrand).

Written by: Peter Stronach

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