Moult in Honey Buzzard and Common Buzzard

Moult in Honey Buzzard and Common Buzzard

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	Jan-Mar	April	May	June	July	August	Septemb	October	Nov-Dec	Sources
Honey Buzzard adult female	Comp-lete to P10	None	Minority start	Most Start	Continue	Suspend at P3-P4	None	None	Resume	1. p35; 2. p22
Honey Buzzard adult male	Comp-lete to P10	None	None	None	Possibly P1-P2	Suspend at P1-P2 (if started)	None	None	Start/ Resume	1. p35; 2. p22
Honey Buzzard first-summer	None	None	None	Possibly some start	Continue	Continue	Continue	Continue	Comp-lete to P10	1. p35; 2. p22
Common Buzzard adult female	None	Start	Continue P4/P5 23/5/2003	Continue	Continue	Continue P8 30/8/2003	Continue	Com-plete to P10	None	1. p269; 2 p189
Common Buzzard adult male	None	None	Start	Continue	Continue P5 16/72003	Continue	Continue P7 12/9/2003	Continue	Com-plete to P10	1. p269; 2 p189
Common Buzzard first-summer	None	Minority start	Most started early in month	Continue	Continue	Continue	Com-plete to all but outermost few (P7?)	None	None	1. p269; 2 p189

Notes:

Primary moult is descendant, starting with P1 and finishing with P10.
Juveniles do not start primary moult until at least the spring following their fledging.
Common Buzzard considered here is nominate buteo.
In Common Buzzard secondaries are moulted after P4 or P5 is shed (source 2, p.189).
In Common Buzzard tail feathers are moulted at same time as remiges, starting from T1 outwards (source 2, p.189).
Rule of thumb is two weeks a primary feather with 5 months (20 weeks) being the usual time to replace all 10 feathers.
Honey Buzzard females on this basis will take about eight weeks to moult four feathers. If starting during incubation moult will last from early June--late July (perhaps typical) or at outside from mid-May--mid-July (earliest) and late June--mid-August (latest).
Timings in italics are those found in present study.
Observations for Common Buzzard above from present study are assigned to sex on whether moult appears early (females) or late (males). The sexes of the birds have not been actually determined.

Comments:

Moult is very useful information from June to September for identification purposes:
A 'buzzard' moulting in Britain beyond P4 is most likely a Common Buzzard.
A 'buzzard' from June to mid-July (before Common Buzzard juveniles fledge) with no primary moult is most likely a Honey Buzzard male (or late starting Honey Buzzard female).
A 'buzzard' from mid-July to September with no primary moult is either a Honey Buzzard adult/juvenile or a Common Buzzard juvenile.
A 'buzzard' family party in late August or early September containing only full-winged birds must be considered as a strong contender for being that of a Honey Buzzard.
As with all identification features, moult should be used in combination with other factors before reaching a decision. Photographs of birds in flight against the light show any moult well.
The state of moult is determined by looking at both wings. Symmetry or near-symmetry in the gaps (feathers missing) suggests that the missing feathers are due to moult. Asymmetry such as a bird missing P8 on one wing and with the other wing complete may indicate feather damage due to natural incidents or interference by man such as being shot at.

Sources: