Here are the basics to understanding molt. I discuss the Humphrey-Parkes classification.
-Molt is the process by which birds replace their feathers.
-Molt is extremely important to a bird’s survival
-All but the largest birds replace all of their feathers every year
-Some birds replace some or most of their feathers again prior to breeding season
There are four terms used to classify molt strategies. Molt is either Simple or Complex, and is either Basic or Alternate.
Simple: Molt strategy is called simple if the juvenile bird holds their juvenile feathers until the next year’s molt
Complex: Molt is called complex if the juvenile replaces some of their feathers shortly after fledging into what is called a formative plumage.
Basic: Molt is called basic if there is just one molt annually, usually a complete molt of all feathers and usually shortly after breeding season.
Alternate: Molt is called alternate if there is a second molt each year, usually prior to breeding season.
So here are the four listed with a summary of the year’s molts:
Simple Basic Strategy:
Bird hatches, grows juvenile feathers, keeps these feathers for a full year and has a pre-basic molt the following year into their adult basic plumage. Each year there is another pre-basic molt.
The difference here is that the juvenile replaces some of their feathers after fledging in a pre-formative molt into a formative plumage. Then each year they undergo one molt of all of their feathers in a pre-basic molt.
These species hatch, grow their juvenile feathers and keep these feathers until they begin their first pre-alternate molt before their first breeding season into their alternate plumage. (some species may breed the first year, others not, but either way they have this first pre-alternate molt) Then after breeding season they have a complete molt, called their pre-basic molt into their basic plumage. In years to follow these species have two annual molts, a pre-basic molt into basic plumage and a pre-alternate molt into alternate plumage.
Species with this strategy hatch, grow their juvenile feathers, and undergo a partial molt after fledging called their pre-formative molt into their formative plumage. They then undergo a partial molt, the pre-alternate molt, into alternate plumage. Then they undergo a pre-basic molt, usually after breeding season into their basic plumage. Each year they have two molts, a complete pre-basic molt, and an incomplete pre-alternate molt into alternate plumage.
To see this graphically check out the table in Howell’s excellent article at: