Monthly Archives: January 2017

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A nice flock of White-winged Scoters

by Guillermo Rodríguez

Although White-winged Scoter is very common in winter along the east coast of the US and Canada, they are rarely found close enough to shore to see plumage details, or at least rarely in large numbers. In late November 2016, a huge flock of this species built up off Crane Beach, Massachusetts. The 700+ birds were feeding on an unidentified species of mollusk for a period of roughly one week, very close to shore (at least by scoter standards). The Crane Beach flock provided an exceptional opportunity to study a large number of individuals, which I couldn’t let pass. Despite the freezing ocean breeze on a very windy day, I managed to take a good number of pictures that show the variability of some key characters well.

Below I present a small sample of my pictures from that day, with the goal of revisiting and testing some of the identification and ageing criteria (presented in eg Garner et al. (2004), Reeber (2016)).

WARNING! This post contains many pictures!

All photos were taken on November 23rd, 2016, in Massachusetts. Note that due to the warm light of the sunrise most birds look very brown-tinged, but they usually look much darker in the overcast light conditions that are typical of NW Europe.

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The mollusk they were feeding on – Eastern Slippery Shell?

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White-winged Scoter: a juvenile male (right at the center) with three adult females and three adult males.

Adult males (including second-years)

Here are some pictures of adult males showing the variability of the bill pattern, the white tick mark at the eye, and the extension of brown on the flanks. As is well known, the characteristic head shape and the bill pattern allow a straightforward separation from both Stejneger’s and Velvet Scoters.

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White-winged Scoter, adult male.

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White-winged Scoter, adult male. Note the particular shape of the flank feathers.

This male (below) presents a “hint of horn”, not very different from that shown by some Stejneger’s (see, for comparison, the Stejneger’s seen in December in Alicante, Spain), and a quite equilateral nostril. The “two-stepped” head profile, lacking the oval, eider-like shape of Stejneger’s, is still very obvious.

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White-winged Scoter (left) and the recent Stejneger’s Scoter (right) from Alicante, Spain. The Stejneger’s picture © Jana Marco, one of the finders of this mega!

Some second winter individuals completely lack the white mark behind the eye, whereas in others it’s present but is still shorter than in older birds. Head and bill shape, including the markedly two-stepped profile, is usually not fully developed at this age and some still show a relatively flat head profile. Bill tip is uniformly pink, with thicker black margins than in adults. Lack of the tricolored bill pattern of adults is also typical of a young age. Some of these young adult males seem to lack the brownish feathers on the flanks, and look more uniformly black than adults.

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White-winged Scoter, second year male, lacking white tick mark.

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White-winged Scoter, second year male, with limited eye tick mark.

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White-winged Scoter, “young” adult male (presumed 2w), showing typical immature features such as greyish iris and pink bill, lacking any yellowish or orangeish tones.

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White-winged Scoter, adult male (left) and a male showing some immature traits (right), eg short eye tick mark, pink bill and not fully developed bill knob.

[Ageing female-type birds]
Ageing of female-plumaged birds is often simple, as many adult females are completely dark and even jet black. Differences in the head shape, the shape of the wing coverts (which are uniformly fresh and rounded in juveniles, and more squared in adults) and the paler belly in juveniles are also supportive. However, the most important feature for me is probably the pattern of the GCs and, in particular, the presence of white tips. The pattern is usually difficult/impossible to see when the birds are on the water, so it usually requires pictures in flight:
adult females: completely dark inner GCs, but the white tip sharply increases in size in the meadial GCs and can occupy almost the entire feather
first-year males: usually a small spot at the feather tip, of uniform size in all the Gcs or at most a gradual and slight increase, but always occupying <50% of the feather
first-year females: very small or completely absent white spot in all GCs

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White-winged Scoter, adult female: note largely white medial GCs, bright reddish feet, squared wing coverts, very broad primaries.

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White-winged Scoter, adult female.

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White-winged Scoter, first winter male: limited amount of white in the GCs

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White-winged Scoter, first winter male.

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White-winged Scoter, first winter female.

I guess ageing criteria are the same for Velvet, but I never had the chance to look into the subject in detail in Europe (Velvet is regular but scarce in Spain). I usually find it problematic to understand the pattern and variability of s1, which is sometimes described as the key feature to age these scoters, so I won’t make further comments on this feature.

Adult females

Adult females vary from very dark birds (looking like a “dirty” version of adult males) to those having the more classic brown plumage with two pale areas on the face. I think that the first type is actually much more common than the latter; the number of these overall black birds within the population appears to be only slightly lower than the number of adult males eg from a sample of 205 birds, 14.6% were adult males and 12.2% were these black presumed females. I wonder if there is an age-related variability, and the black birds are actually the older females.

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White-winged Scoter, adult female.

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White-winged Scoter, adult female: note the squarish shape of the wing coverts.

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White-winged Scoter, adult female.

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White-winged Scoter, female: dark below, slight bill bump, apparent bright feet, not very uniform back feathers… not sure about the age, could this bird be an adult?

The black-plumaged individuals are sometimes identified as first-year males with an extensive first pre-formative moult, but I think this explanation can be safely ruled out based on the GCs pattern (see the shots in flight above), the bright color of the feet, the dark irises, and the squared wing coverts shown by most of these birds. Only when the formative moult is much more advanced, around late January/February, first-winter males look similar, although with a much dirtier plumage, often looking “patchy” and not as uniformly jet black.

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White-winged Scoter, two adult females with a first-year male (right).

The head shape of these birds actually recalls that of adult males, due to a squarish head with a flat crown, a straight (non-concave) forehead profile and the hint of a bump at the bill base, leading to a two-stepped head profile, although it is much smoother than in males. Although the differences are sometimes subtle, I think these features are distinctive enough to allow separation from Velvet in most cases. Take a look at this compilation to get a sense of the variability in head and bill shape in adult females:

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White-winged Scoter, adult females: variability in head and bill shape.

Note that some adult females present some diffuse pink “brush-strokes” at the bill tip, but the iris seems to be pretty dark in all the individuals (cf first winter males, see below).

First-year males

By late November, juveniles still look very fresh, and the pale velvet at the base of the bill often looks nicely neat. Around 40-50% show what seem to be signs of moult around the face, and a few males have already developed a pale greyish iris and pink in the bill. But even birds that still have a completely juvenile appearance can be readily sexed by the elongated bill and very flat head profile, in contrast to females, which show a shorter bill and often a slightly angular (concave) head profile.

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White-winged Scoters, first-year male (left) and first winter female (right). In my opinion, many juveniles can be reliably sexed in the field on grounds of the head and bill shape. Note, on the back, another first year female (left) and first year male (right).

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White winged Scoter, first year birds. Sexing is definitely not always possible – this bird (center) looks intermediate, or perhaps on the female side?

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White-winged Scoter, first-year male: a nice bird still in completely juvenile plumage.

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White-winged Scoter, first-year male: gradual lightening of the iris, traces of moult around the face.

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White-winged Scoter, first-year male. This looks like a VERY advanced first year male.

Regarding the separation from Velvet, in addition to the head shape, the shape of the feathering at the base of the bill is quite distinctive given sufficiently close views; it extends further onto the bill than in Velvet and forms a 90-degree angle in the lower corner, always below the position of the nostril. A few more examples of (presumed) first-year males:

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White-winged Scoter, first-year males: variation in head and bill shape.

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White-winged Scoter, first-year male. Interesting individual with a narrow bill, and relatively rounded shape of the feathering at the lower corner of the bill base.

First-year females

Undoubtedly the most problematic group, many first-year females look very similar overall to Velvet Scoter. With short bills, and often concave and rounded head profiles, it may be extremely difficult to pick one out among a flock of Velvets. However, the shape of the feathering at the base of the bill, even if it is not as distinctive as it is in males, is still quite a good character when properly seen. Most birds (>60-70% ?) clearly show, below the nostril, a right angle:

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White-winged Scoter, first-year female.

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White-winged Scoter, first-year female.

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White-winged Scoter, first-year females. In a few juveniles, the pale spots merge, giving a striking appearance.

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White-winged Scoter, first-year female – convex and rounded head profile, similar to Velvet.

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White-winged Scoter, first-year female: variation in head and bill shape.

In a few birds the angle is not as sharply defined, looking rounder and closer to the nostril, and the pattern is probably consistent with Velvet. But this seems to be the exception and not the norm!

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White-winged Scoter, first-year female, showing a rounded corner of the feathering at the bill base.

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White-winged Scoter, presumed first-year female.

Variation in adult Cabot’s Tern and Sandwich Tern

By Yoav Perlman

With special assistance from Mike Langman and Guillermo Rodriguez

These two tern species from both sides of the Atlantic look very similar, but in fact are not even the closest relatives – based on genetics, Cabot’s Tern was found to be a sister species of Elegant Tern. Sandwich Tern Thalasseus sandvicensis is monotypic, and Cabot’s Tern includes Thalasseus a. acuflavida and another taxon – Cayene Tern T. a. eurygnatha. This post deals only with nominate acuflavida.

In his Challenge Series Autumn book, Martin Garner dedicated a chapter to them. And of course there’s Garner et al. 2007 DB article. Though not a frequent visitor to Europe as other American gulls and terns, the potential to find a Cabot’s Tern in Europe remains, in light of records of both taxa on both sides of the Atlantic. Additionally, one individual in October 2016 on Tereceira, Azores in October 2016 was first claimed as Cabot’s Tern and caused a bit of a headache. Therefore, I think it is worth revisiting the main ID criteria to separate the two species. I must stress that I am no expert on Cabot’s Tern ID, so I hugely appreciate the valuable help I received from Mike Langman, Guillermo Rodriguez and Julian Hough who certainly are experts. In this post I will try to demonstrate some variation in both species regarding main ID criteria, but I think that still most individuals can be safely identified, within the known limits of variation. That’s why it’s important to document and acknowledge this variation in both species.

Bill structure

The thumb rule is that Cabot’s Tern has a thicker, heavier-based and straighter bill, with an obvious gonydeal angle. Not quite Great Black-backed Gull gonys, but it is still there. Most literature mentions that Sandwich Tern has a proportionately longer bill, without any gonys (really?), and a distinct drooping tip.

I don’t know much about bill development in terns, but I know that in gulls very often adults have heavier bills than young birds, with more pronounced gonydeal angle. The same goes for sexual differences in bill structure – male gulls have larger and heavier bills than females. So possibly some variation in tern bills is age and sex related?

This is a nice, heavy-billed Cabot’s Tern (in April, I know…) showing a pronounced gonys:

Cabot's Tern, High Island, Texas, USA, April 2016. Photo by Guillermo Rodriguez

Cabot’s Tern, High Island, Texas, USA, April 2016. Photo by Guillermo Rodriguez

This Cabot’s Tern has a slightly thinner bill with almost no gonys, but it is still very straight, lacking the drooping tip of a sandwich.

Cabot's Tern, High Island, Texas, USA, April 2016. Photo by Guillermo Rodriguez

Cabot’s Tern, High Island, Texas, USA, April 2016. Photo by Guillermo Rodriguez

This is a typical Sandwich Tern, with a long, slender bill, distinctly downcurved, and lacking any gonys:

Sandwich Tern, Arrecife , Lanzarote, Canary islands, September 2011. Photo by David Perez

Sandwich Tern, Arrecife, Lanzarote, Canary Islands, September 2011. Photo by David Perez

Though some Sandwich Terns show a rather pronounced gonys, the bill always looks slender and downcurved:

Sandwich Tern, Arrecife, Lanzarote, Canary islands, October 2011. Photo by David Perez

Sandwich Tern, Arrecife, Lanzarote, Canary Islands, October 2011. Photo by David Perez

Note also that in literature it is mentioned that on average, adult Cabot’s Terns shows a more extensive yellow tip to the bill than Sandwich Terns. There is lots of variation in this, and I suspect that like in other terns this variation in bill tip pattern may be related to breeding condition and sex.

Pattern an overall ‘darkness’ of primaries

Cabot’s Tern has generally darker primaries than Sandwich Tern. There is a difference between the two species in both the base colour of the primaries, and the width of the pale fringes to each primary, especially on the inner web. Sandwich tern also shows a pale ‘hook’ on the outer webs of old and new primaries, while Cabot’s tern apparently never has pale markings on the outer webs. It should be noted that in both species, old and worn primaries before moult are darker and have narrower pale fringes, so a worn Sandwich Tern just before moult can look as dark as a freshly-moulted Cabot’s Tern. Therefore, it is important to understand whether the primaries used for identification are fresh or worn.

This is a typically dark-winged Cabot’s Tern, in late September:

Cabot's Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman.

Cabot’s Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman.

Check this individual, also in late September: it has an overall paler wingtip, with rather broad pale outer webs. Also, it is not easy to understand the exact pattern of the worn outer primaries. Seem to have no pale on the outer webs but I’m not sure what exactly is going on there:

Cabot's Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman.

Cabot’s Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman.

Sandwich Tern typically gives a pale impression to wingtip, with prominent pale inner and outer webs to outer primaries, that it had almost completed moulting in October:

Sandwich Tern, Arrecife, Lanzarote, Canary Islands, October 2011. Photo by David Perez

Sandwich Tern, Arrecife, Lanzarote, Canary Islands, October 2011. Photo by David Perez

This September Sandwich Tern has a really dark wingtip, with very narrow pale fringes to visible outer primaries:

Sandwich Tern, Salinas de la Tapa, Cadiz, Spain, 9 September 2011. Photo by David Perez.

Sandwich Tern, Salinas de la Tapa, Cadiz, Spain, 9 September 2011. Photo by David Perez

Moult (or molt?) timing

There is some conflicting information about this. Adult Sandwich and Cabot’s Terns perform an arrested moult, in which it replaced 5-6 inner primaries before migration, and then the rest after migration. In ‘Challenge Series Autumn’ Martin Garner wrote that Sandwich Tern moults earlier than Cabot’s and mentions that Cabot’s moults the outer primaries late, in December – January, with some individuals showing unmoulted primaries in March. Pyle mentions in his book that Cabot’s moult P8-P10 Between October and March. Malling Olsen and Larsson even write in their tern guide that P10 can be moulted between March and June. Quite a broad temporal window. And to make it even more complicated, according to the brand new BTO guide Identification of European Non-Passerines, some Sandwich Terns complete their moult by late October, while others complete this moult only in winter. So a complete or near-complete moult in mid-autumn (October) indicates Sandwich Tern, but it doesn’t seem to work the other way – late moult in late autumn (November – December) does not necessarily exclude Sandwich Tern. Using early moult to identify a vagrant Sandwich in North America is fine, but late moult is not necessarily a sign for a vagrant Cabot’s in Europe.

Crown pattern

Basically, Cabot’s Tern has darker and more solid rear crown, with longer feathers and very few if any white tips. Crown is rather clean white. Cabot’s also tend to show more black around and in front of the eye. Not sure about this one… Sandwich Tern has a paler rear crown, with more white tips – often referred as ‘peppered’ rear crown. There are more dark feathers on the crown itself. However… variation here too. Quite a peppered rear crown on this September Cabot’s. Top crown is clean though.

Cabot's Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman.

Cabot’s Tern, Tulum, Yucatan, Mexico, 25 September 2016. Photo by Mike Langman

This is a more normal-looking Cabot’s tern, with a rather solid black rear crown, though there are quite many white feathers mixed. Very clean white crown. But oh no, look at the pale ‘hook’ around the primaries…

Cabot's Tern, Florida, USA, 21 January 2007. Photo by Julian Hough.

Cabot’s Tern, Florida, USA, 21 January 2007. Photo by Julian Hough.

A beautiful demonstration of the dirty crown of Sandwich Tern:

Sandwich Tern, Ijmuiden, Netherlands, 23 September 2012. Photo by Marten Miske

Sandwich Tern, Ijmuiden, Netherlands, 23 September 2012. Photo by Marten Miske

Check the rather solid dark rear crown of this October Sandwich Tern:

Sandwich Tern, Norfolk, UK, October 2016. Photo by Mike Dawson

Sandwich Tern, Norfolk, UK, October 2016. Photo by Mike Dawson

Terceira, Azores, October 2016 individual

This individual was on the Nearctic magnet archipelago last October. Some friends are writing about this individual so I will refrain from expressing my view on it. Here are some images – judge for yourself:

... Tern, Terceira, Azores, October 2016. Photo by Mika Bruun.

… Tern, Terceira, Azores, October 2016. Photo by Mika Bruun.

... Tern, Terceira, Azores, October 2016. Photo by Mika Bruun.

… Tern, Terceira, Azores, October 2016. Photo by Mika Bruun.

... Tern, Terceira, Azores, October 2016. Photo by Daniel Mauras.

… Tern, Terceira, Azores, October 2016. Photo by Daniel Mauras.

In the next episode – hatch-year birds…

Many thanks to all the talented photographers, to Killian Mullarney and to Nick Watmough who contributed to this post!

Sykes’s Nightjar – new to Oman

By Yoav Perlman

Happy New Year to all our followers. Hope you had a great holiday.

I received this nice story from two Spanish birders who visited Oman in December 2016 – Albert Burgas and Àlex Ollé. Oman is a true frontier for WP birders – such an amazing country with strong Afrotropical and Asian influences. So many birds waiting to be found there. Must visit there soon. And I love nightjars… Anyway, here is their story:

During a short trip to Oman in December 2016 we visited Muntasar Oasis in central Oman (19°27’11.8″N 54°37’13.9″E) on the 12th. We had a rewarding dusk encounter with a lovely Egyptian Nightjar Caprimulgus aegyptius, hunting and sitting in front of us at Qatbit Oasis. We watched two Mountain Gazelles Gazella gazella cora and one Jerboa sp. when a relatively small and pallid nightjar flew in. It had large and well marked white wing spots and prominent white tail corners, excluding Egyptian Nightjar. At that moment we speculated that it could be a European Nightjar Caprimulgus europaeus. However, European Nightjar is a familiar species for us and that nightjar looked different. The bird was flying and sitting regularly, so we decided to approach the bird with a spotlight. We approached it down to barely two meters and got some photos. At that moment it was obvious that we were not watching a European Nightjar, based on its smaller size, different jizz and pallid colouration. With the available information we had at that moment we supposed that it was a Nubian Nightjar Caprimulgus nubicus as the most probable species. That would be the 8th record for Oman. 

A few days later back home we revisited the issue of the intriguing nightjar. Checking on Internet for other nightjar species from neighbouring countries around Oman we found Sykes’s Nightjar Caprimulgus mahrattensis. That fitted 100% with the bird we photographed, but a far more unexpected species than Nubian Nightjar. We sent the pictures and description to renowned ornithologists from the Middle East to confirm our identification. 

Sykes's Nightjar, Muntasar Oasis, Oman, December 2016. Photo by Albert Burgas.

Sykes’s Nightjar, Muntasar Oasis, Oman, December 2016. Photo by Albert Burgas.

Sykes's Nightjar, Muntasar Oasis, Oman, December 2016. Photo by Albert Burgas.

Sykes’s Nightjar, Muntasar Oasis, Oman, December 2016. Photo by Albert Burgas.

Sykes’s Nightjar breeds in south-east Iran, south Afghanistan, Pakistan and north-west India. It migrates in winter to west, north and central India. There are only four previous records of Sykes’s Nightjar in the Arabian Peninsula, all of them from the UAE and always found between the end of December and February (Oscar Campbell pers. com.). Pending acceptance by Oman Rarities Committee, this is the 1st record of Sykes’s Nightjar for the Sultanate of Oman and the 5th for Arabia.

Some notes on ID by YP:

I am no expert on Sykes’s Nightjar, but this looks good. It is not a Nubian Nightjar – main difference is the throat pattern: Nubian has a well-patterned throat, with a pale moustachial stripe and a whitish throat. Also, Middle Eastern Nubian Nightjars tend to be more heavily marked overall, but this can show very different in photos, depending on the misleading ‘flattening’ effect of spotlighting on photos, and image processing.

'Tamarisk' Nubian Nightjar, Neot Hakikar, Israel, October 2011. Photo by Yoav Perlman.

‘Tamarisk’ Nubian Nightjar, Neot Hakikar, Israel, October 2011. Photo by Yoav Perlman.

Egyptian Nightjar is larger and longer-winged, and lacks the complete rufous neck collar both species above show.

Egyptian Nightjar, Dead Sea, Israel, December 2016. Photo by Yoav Perlman.

Egyptian Nightjar, Dead Sea, Israel, December 2016. Photo by Yoav Perlman.

Egyptian Nightjar, Neot Hakikar, Israel, March 2012. Photo by Yoav Perlman.

Egyptian Nightjar, Neot Hakikar, Israel, March 2012. Photo by Yoav Perlman.

For comparison, here are two Sykes’s Nightjars from Gujarat, India – courtesy of Mike Watson. There seems to be some variation in the extent of black markings on the scapulars between these individuals and the Oman bird.

Sykes's Nightjar, Gujarat, India, February 2015. Photo by Mike Watson.

Sykes’s Nightjar, Gujarat, India, February 2015. Photo by Mike Watson.

Sykes's Nightjar, Gujarat, India, February 2015. Photo by Mike Watson.

Sykes’s Nightjar, Gujarat, India, February 2015. Photo by Mike Watson.

Many thanks to Àlex and Albert for contacting me and sharing their exciting discovery.