1st-year Red-tailed Hawks Molting in Fall

17 January 2016

1st-year Red-tailed Hawks Molting in Fall

by Frank Nicoletti & Jerry Liguori

We know that most raptors wear their 1st-year (juvenile) plumage for about a year, and begin to replace their feathers during their first spring (usually starting in March or April), but are you aware of the phenomenon where some 1st-year Red-tailed Hawks actively molt flight feathers in their first fall? Sounds odd, but this unusual type of molt has been documented at Hawk Ridge, Duluth MN in certain falls where 1st-year Red-tailed Hawks are photographed that possess varying amounts of adult flight feathers. As of now, it seems to occur in the Eastern race (B.j. borealis) and the heavily marked form of Eastern called ìNorthernî (B.j. abieticola), but more study is needed to understand if this occurs in other populations of Red-tailed Hawks. This ìfall moltî has only been seen a handful of other times, specifically on Cooperís Hawk, Merlin, and Broad-winged Hawk.
    
It has been documented that some 1st-year birds (all species) exhibit ëadventitious moltí - losing random feathers for unknown or assumed reasons, such as trauma or natural consequences rather than design or inherent nature. When this happens, the randomly lost feathers are replaced by adult-like feathers (that show an 'in-between' appearance from 1st-year to adult), or feathers showing a perfect adult pattern. This often depends on exactly how old the bird is, or how active its hormones are. However, the reason some Red-tailed Hawks actually undergo a partial sequential molt in fall is unknown. Theories as to why this partial molt occurs ranges from stress due to West Nile Virus to a response to parasites. Interestingly, it seems that they halt their molt before winter, and do not undergo a complete molt, as seen through documenting wintering birds. It also seems that documentation of 1st-year raptors of other species molting in fall is lacking.

Check out these photos below of 1st-year Red-tailed Hawks caught in fall at Hawk Ridge, MN by Frank Nicoletti and Step Wilson, note the replaced adult tail feathers (reddish and unbanded) and adult remiges throughout Figures 1-2. Figures 3-5 illustrate birds with either replaced tail feathers or tails that show a mix of adult and 1st-year characters.

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