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Plumage score, age and gender in Icelandic Godwits

Plumage score

 During the spring (pre-nuptial) and autumn (post-nuptial) moult, adult godwits can be classified according to their plumage state. The plumage scoring system we use is based on the proportion of coloured (i.e. orange and black) summer plumage feathers. Some of the summer plumage feathers are grey, but these cannot easily be distinguished from winter plumage feathers. Plumage score is therefore an estimate of moult stage, but also provides information on the extent of coloured summer plumage on individual birds.

Despite some gender differences (females tend to have a duller breeding plumage than males), scoring the plumage of individual godwits and of samples of birds within flocks can provide very valuable information on the timing and rate of moult of birds in different parts of the range.

The scale to attribute a plumage score to an individual godwit is as follows:

Score

Quantitative parameters

Appearance in the field

1

All plumage grey and white

2

A few coloured feather
(usually on the back or chest)

3

Primarily grey with some coloured feathers (on back
or chest, often with light barring on the belly)

4

Looks mostly orange (some grey
throughout the back and barring on the belly)

5

Looks orange (mostly coloured
feathers and black barring on belly)

6

Just the odd grey feather

7

Almost entirely orange, black and white feathers

Gender

Gender can also be recorded on the field, as this species is sexually dimorphic. However, the genders overlap in size and so not all birds can be definitely assigned a gender. During the breeding season, males and females are easily identified, especially when they pair up and the brighter and more extensive male plumage is apparent. During winter, however, plumages are similar for both sexes. Despite some overlap, the characteristics that best separate males from females are as follows:

I. Breeding plumage: Males tend to have much less grey plumage on the back, the orange feathers are often brighter than in females and the grey on the head is often darker than in females. In addition, strong black barring on the belly is highly indicative of a male, with females tending to have only weak or no barring.

II. Body Size: Females tend to be larger than males. A big female is easy to determine when a small male is close providing a relative measure of size. However, this is not always the case so this can be a bit tricky.

III. Bill length: Females tend to have a longer bill and than males. In the field bill length can generally be used to reliably sex large females and small males, although birds with intermediate bill lengths are quite common and these cannot be sexed without additional plumage characteristics.

Age

Juveniles godwits can be identified during the first few months after fledging by the buff-orange feathers on the chest, neck and head. In addition, the covert feathers on the wings often show a brownish line around the tips from which an overall brown and “lined” heterogeneous pattern arises. However, these characteristics gradually disappear during the first autumn moult and many will be indistinguishable from adult by late autumn/early winter. Many juveniles do not return to breed in their first summer, and these birds tend not to gain full summer plumage in their first summer.

Plumage Scores in pictures

Below is a set of two photos for each plumage state, with the exception of the first stage for which there is only one image. This selection is not an exhaustive depiction of all possible plumage states, but shows the commonest variation between the first level of a given score and the most advanced level achievable within the same score. So for instances the left picture for Plumage Score 2, is a godwit with only one orange feather (on the shoulder) while the right picture shows another godwit just before turning into a Plumage Score 3. For this reason, there might be a slight degree of overlap between the right image of a given Plumage Score and the left image of the following Plumage Score.

Plumage 1

Plumage 2

Plumage 3

Plumage 4

Plumage 5

Plumage 6

Plumage 7

Juvenile Plumage

 
 

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