Ageing Greenshanks, February 2019

At the beginning of February 2019, in one of my regular incursions to the Óbidos Lagoon, I found two Greenshanks (Tringa nebularia). The birds were relatively close, feeding on the edge of the pond. I took some photos with the purpose of practicing ageing Greenshanks, at a time of the year when it is more difficult.

I have always found, with some exceptions, relatively hard to age waders. The great variability in feather patterns and the intensity and extent of moult, makes some plumages difficult to interpret.

Summary of the moult in Greenshanks:

Adults

Post-nuptial - Complete. A part of the individuals begins primary moult still in the breeding grounds and suspends it during migration, resuming it in the wintering areas. Others begin primary moult already in the wintering areas.

Pre-nuptial - Partial. Variable, but usually includes replacing body feathers, some coverts and tertials.

Juveniles

Post-juvenile - Partial. Includes a variable number of coverts, body and tail feathers.

Pre-nuptial - Partial. Variable, but, as in adults, it can include multiple coverts, tail feathers and tertials. Some birds can moult outer primaries (Prater, et all, 1977).


The separation of 1st winters from adults, in autumn, is relatively easy. One of the most mentioned characters in the literature is the shape of the median coverts. Where the typical median covert has a clear pale fringe, interrupted at the tip by a brown split (Fig. 2). The bird in Fig. 1 is a 1st winter that has undergone a post-juvenile molt restricted to the scapulars, and most likely, during autumn, will replace a variable number of lesser, median and greater coverts. The tertials are juvenile, told by the brownish coloration and weak pattern, but some individuals can present gray tertials with a more defined pattern.

Fig. 1 - Pattern of median coverts. Juvenile (left), adult (right).

At the beginning of the winter, juveniles have already renovated a good part of the coverts during their partial post-juvenile moult, resembling adult plumage. Knowing that adults undergo a complete post-nuptial moult, to identify immature birds one must look for juvenile feathers that remain unmoulted. This task is increasingly complicated as winter progresses, mainly because feather wear tend to blur significant differences in plumage patterns.

One factor to take into account is the inferior quality of juvenile feathers, that lead to a slightly more pronounced wear than in adults. This wear is particularly evidenced by the coloration. For example, lesser and median coverts tend to be browner in immature birds than in adults.

Another feature that can help separating age groups at the end of winter is the wear, shape and coloring of primaries and secondaries. In my opinion, this is one of the most reliable characters, since it is less subject to variability than the coverts. Given the Greenshank moult pattern, immature should keep juvenile primaries, sometimes until the next complet moult (August-October). Some caution is needed during spring, as there seem to be some immature birds that renew the outer primaries, which would result in birds presenting the tip of the  primaries "fresh", when observed in the field. In this case, a photograph with an open wing is required to see the moult limit, between the outer primaries (adult type) and the inner primaries (juvenile).

Fig. 2 - Greenshanks, Óbidos lagoon, West Portugal, February 2019. Bird 1 (front), bird 2 (back).

The two birds, I observed in Lagoa de Óbidos, showed a slightly different coloration of the upper parts. The bird 1 (front in the photo), presented grayer shades in most coverts, I classified this bird as adult. The bird 2 (back in the photo) had some brown coverts, as well as flight feathers, a little more worn, I classified this bird as immature (2nd calendar year).

Fig. 3 - Greenshanks, Óbidos lagoon, West Portugal, February 2019. Bird 1 (front), bird 2 (back).

In this photo we can see the head pattern, which is slightly different in the two birds. Bird 1 (front in the photo) features a whiter throat and bold gray stripes on the side of the neck . On bird 2 (back in the photo) the stipped pattern on the neck is thinner and less defined, creating a less "clean" appearance of the head and neck.

Fig. 4 - Greenshanks, Óbidos lagoon, West Portugal, February 2019. Bird 1 (front), bird 2 (back).

Bird 1 (front in the photo), also has two tertials, in the left wing, very "fresh" and gray. I am not sure if they were renewed in a late post-nuptial moult or in the pre-nuptial moult. Therefore, it is quite possible that the bird is in active moult of coverts and / or body feathers.

Fig. 5 - Greenshank, Óbidos lagoon, West Portugal, February 2019. Bird 1.

Bird 1 -  Flight feathers with little wear, presenting a well defined white edge in secondaries and  inner primaries. The upper parts have a greater uniformity of coloration, with the lesser and median coverts dark gray.

Fig. 6 - Greenshank, Óbidos lagoon, West Portugal, February 2019. Bird 2.

Bird 2 - Primaries and secondaries with some wear, showing a weak white trailing edge.  The upper parts have areas with light brown coverts, particularly in lesser and median coverts. Note the  innermost great covert of the right wing, showing a good amount of wear.

Fig. 7 - Detail of flight feathers. Bird 2 (left) and bird 1 (right).

Comparison of the shape and level of wear on the primaries and secondaries. (Bird 2 - left, Bird 1 - right). Note the broader upper edge of the flight feathers on bird 2, creating a more "blunt" tip, characteristic of juvenile feathers.

Fig. 8 - Detail of tail feathers, bird 2.

The wear and pattern of the tail feathers, in particular of R1 and R5, has been mention out as a way to separate juveniles and adults. I believe it may work in some inds., although In the case of these two birds, from what I could perceive in the field and in the photos, it seems to me that both replaced the tail feathers, making it useless as an ageing criteria. 

Conclusion

Ageing Greenshanks in late winter, or early spring, can be a tricky task. The extent of post-juvenile moult can lead to some individuals getting plumages very much like adults. So when we come across a Greenshank we should take into account the following:

- Check if there are any median coverts with the typical juvenile pattern;

- See if different generations of feathers occur in the coverts, in particular, if there are brownish feathers and with enough wear on the upper parts. There must be some caution because adults, at the end of winter, can also exhibit different generations of feathers, as a result of partial pre-breeding moult. Immatures will show old brownish feathers, not gray;

- Observe the wear on the primaries, if it has wear, the bird should be an immature;

- In the literature it is mentioned that some immature birds can moult the outer primaries in the pre-nuptial moult. I do not know exactly how much this happens in the populations that winter or migrate through Portugal. So, if a bird in late winter, or early spring, displaying "fresh" primaries tip may be an immature one. In this case, it is necessary to check for juvenile coverts or, if an open wing photo is obtained, if there are moult limits on the inner primaries.

- If you get an open wing photo, we can also observe the shape of the primaries and secondaries, which apparently seems to be different in adults and immature birds (I need to test this theory better);

- To verify the wear of the tail feathers, some juveniles seem to retain some tail feathers in the post-juvenile molt.

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Acknowledgments

To Peter Potts, Pedro Lourenço and Leila Durte.

References

Demongin, L. 2016.  Identification guide to birds in the hand. Laurent Demongin (privatly publish)
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Message, S. and Taylor, D. 2005. Field Guide to the Waders of Europe, Asia and North America. Christopher Helm, London.
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Meissner, W. 2008. Ageing and sexing series. Part 3: Ageing and sexing the Common Greenshank Tringa nebularia. Wader Study Group Bull. 115(3): 182–184.
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Prater, A.J., Marchant, J.H. & Vuorinen, J. 1977. Guide to the Identification and Ageing of Holarctic Waders. BTO Tring.