Interestingly, there are only two other July records of PAGP's in Eastern North America on eBird + 1 from Bermuda. But, there are SEVERAL summer records of PAGP from Great Britain but relatively very few American GP records....
Check out Bruce's page for some further discussion on their occurrence in Newfoundland.
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Here are the 3 photos that helped verify the 4th sighting on the 16th of July, 2015.
Thank you to Mark Amershek for sharing these photos and allowing me to post them here. And thank you to David Trently for sharing the sighting - unfortunately I was away from Internet access when he sent the message so I couldn't forward it to the Newfoundland birders in a timely manner :S
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The above bird can be identified as an adult male due to the solid black face.
To compare, adult American GPs do not have white that extends along the flanks all the way to the tail, and it has a solidly dark undertail. This makes it fairly easy to separate American Golden-Plovers from the two other GP species in their adult plumages.
This adult American GP (probably a female) was photographed in October so is transitioning between adult and winter plumage. Still, it is still easy to tell that it is an American GP, despite the white patches along the flanks and belly, because the white is not continuous from head to tail as in both other Golden-Plover species.
An adult Golden-Plover with white that extends from the head to the tail could be a European or Pacific GP. So we have to look at further details to separate those two species.
In general, European GPs are more bulky compared to the slimmer and more elegant Pacific GP. To add to the elegant body shape, Pacific GPs have slightly longer tibias.
Note the short tibia of the adult European GP above.
Compared to the long tibia of a Pacific GP.
Note in the above two photos that the white extends from the head through the flanks all the way to the tail. But in the Pacific GP, there are small dark patches in the flanks.
Another useful field mark to separate these two species is the undertail colouration. European GPs generally have more white than their Pacific counterparts.
European GP undertail:
Note the more solidly black undertail of the Pacific GP:
In flight, European GPs have white axillaries (i.e. armpits) - this area is grey in Pacific GPs.
Three European GPs in flight showing their white armpits.
In summary, adult Pacific & European Golden-Plovers in alternate (aka summer/breeding) plumage can be separated by close study of the flanks, undertails, axillaries, tibia length, and general body shape. Of course, out of range Golden-Plovers would need more than one, preferably all, of these features to be documented.
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If you think identifying adults was difficult, try juveniles!
I won't write much here, but will show a key feature of American Golden-Plovers that North American birders should be familiar with. If you are familiar with the primary extension of the more regular American Golden-Plovers, you will be more likely to find an interesting juvenile (or winter-plumaged) Golden-Plover that deserves closer scrutiny.
Note the long primary project beyond the tertials. This feature is often confusing because it is not referring to the actual length of the primaries, but the RELATIVE length of the primaries in comparison to the tertials. In fact, the primaries of American GPs are intermediate in length between those of European & Pacific GPs, but they appear longer because they are less concealed by the overlying tertials.
On a standing bird, the primaries extend beyond the tertials of all Golden-Plover species. However, American Golden-Plovers have relatively shore tertials allowing more of the underlying primaries to be visible.
In the above and below photos you should be able to count 4 individual primary feathers that extend beyond the tertials.
European Golden-Plover below:
I think this is a good teaching opportunity, because in the above photo of a European Golden-Plover 5 primaries are visible! BUT, only 3 extend beyond the longest tertial. Those that extend beyond the longest tertial contribute to the primary extension.
To reiterate, 4 primaries extend beyond the tertials in American GPs, and 3 in European GPs. Of course, there are exceptions (especially if a bird is missing a tertial or more!) so look beyond this feature to make a final identification!
And one more European GP photo just for the fun of it:
