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Question about moult score

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Old Wednesday 11th July 2018, 06:45   #1
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Question about moult score

Hi, I have been doing ringing in Hong Kong for a few years. We tried to collect moult stage of birds for understanding their phenology. In general, we followed the BTO's practice to record the moult score, where "5" is assigned for new and fresh feather; and "0" for old feathers.

We sometimes found difficulty on assigning the moult score of birds, especially when the birds are having a full set of fully grown feather. Different ringers sometimes have dispute on deciding whether the feathers are old/fresh. Below is one commonly situation we encountered:

Two Plain Prinias of same age class were trapped. One with fully grown feathers in good condition although they are not newly fresh, i.e. not worn. Another individual has P1 moulting (say, score 2). Other flight feathers are in the same condition as the first individual. In this case, we may give "0" for all feathers for the first bird, and 2 for the second bird. However, when we do not have the second Prinia to compare, we might incorrectly give score "5" for the first bird because the feathers are in really good condition. How shall we improve our decision in a consistent way?

Thank you all.
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Old Thursday 12th July 2018, 08:15   #2
Ross McGregor
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If you are trying to measure the mean population moult start and end date, then just scoring birds as "old" (moult not started), "in moult" and "new" (moult completed) and then applying the method in Rothery, P., & Newton, I. (2002). A simple method for estimating timing and duration of avian primary moult using field data. Ibis, 144(3), 526-528 will give you that estimate.
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Old Friday 13th July 2018, 16:32   #3
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0 and 5 are relative to the majority of the population. The same feathers are 5 at the end of the moult season and 0 at the beginning of the next.

If the population has very variable and protracted moult period, then it really may be difficult to decide between these two. The extreme situation would be that there is no moult season at all, but there are moulting birds in the population year round - then there really is no distinction between 0 and 5. There should be seasonality in your example species Plain Prinia in Hong Kong. Adults and first-years probably have different primary feather moulting season?

In any case, it is not that important - at the end when making the analysis with all the data, you should clearly see which birds are "wrongly" assigned to 0 or 5.
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Old Monday 16th July 2018, 06:17   #4
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Thank Ross McGregor and jalid for the replies. Yes, given that Plain Prinia is a resident species locally, we observed no distinct moult season for this species. That is, birds are moulting year-round, some individuals may even suspend their moulting during breeding season and resume after summer. I am not sure whether I am correct, but in this case, I think it would be very rare to see birds having high moult score (many "5s") as there is no distinct moult cycle except the fully-fledged first-year birds.
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