Fall 2010 Class #2 Focus on Molt

Tonight is all about Molt

Look at the Howell ABA article table of molt.

We will use the Humphrey Parke System.  It’s all about feather growth, i.e. molt.  Not about color.

Other systems are the Calandar Year molt system.  The problem with this is this can be more cumbersome re what year the bird is in, etc.  Pyle uses this.  Another system is the Life Year strategy.  This works good for Northern Hemisphere birds, but is awkward when birds cross the equator.

See article by Howell All You Ever Wanted to Know About Molt but were Afraid to Ask Part II Finding Order Amid the Chaos

Here is a link to the Slater Museum Blog with many posts on birding and other topics to browse

Here is a Dennis Paulson post on Molt.


4 strategies.

Simple Basic Strategy (SBS)

Complex Basic Strategy (CBS)

Simple Alternate Strategy (SAS)

Complex Alternate Strategy (CAS)

Complex means birds shed their juvenile plumage into formative plumage in the first year.

Alternate means the birds have an additional molt each year, almost always a partial molt in each year, usually into breeding plumage.

In HP we talk about cycles, not years.

Here are some terms to learn the definitions of:

Simple Basic: Albatrosses, petrels, barn owls, a few others.  In the fall there is a complete molt in all birds.

Limited: body & head

Partial: this plus some coverts, scapulars

Incomplete: above plus some remiges.

Complete: all feathers.

Complex basic strategy:  In the first cycle only, the bird has a preformative molt into the formative plumage in the first fall.  Then has just one pre-basic molt each year.  This pre-formative molt is usually limited, partial, or incomplete.  Example: towhee.  All black juvenile plumage.  Then they disappear; have a pre-formative partial molt losing all but flight feathers to look like an adult, except for worn primaries.

Simple Alternate Strategy:  In first year birds carry juvenile plumage until the first alternate molt.  This can vary in time from fall to winter. Think large white headed gulls.  Carry juvenile plumage until Sept.  Then have molt of some scapulars, etc. into A1 plumage.  Thereafter each year have one complete basic molt, and one partial alternate molt.

Complex Alternate Strategy:  First year birds have two inserted molts after juvenile.  F1 molt is usually partial, then later in the first year is the A1 molt.  Thereafter each year have a partial PA molt, and a complete PB molt.

Difference between formative molt and basic molt is that the PF molt is usually not complete.  Basic is complete.

Examples:  All passerines have a complex molt strategy.  Look at the table for these by family.

Here is a link to the table Ken used in class.   http://www.prbo.org/cms/docs/terre/Howell%20Birding%20molt%202003%20part%202.pdf

The pre-basic, pre-formative, and pre-alternate terms refer to a molt into the basic, formative and alternate plumages.

How do we recognize molt.  Obviously look for gaps in wings and tails.  If these are present, we say the bird is in active molt. If in active molt the bird is in transition from one plumage to another.

Injury to feathers.  Sometimes if you see a bird with assymetric flight feathers missing, especially not in the fall, it may be damaged feathers.  Birds often replace these damaged feathers.  Some birds suspend molt, and leave gaps for periods of time.

Molt Limits + Molt Contrast is the contrast between the new feathers and the old feathers being replaced. Often in the fall will see bright feathers being replaced by gray or plain feathers.  May see molt limits in the scapulars or coverts.  Sometimes you can age first year birds this way

Feather wear:  new feathers are not frayed, usually rounded and fully formed, don’t droop.  Old feathers often brownish, frayed, and often narrow.  Especially primaries, sometimes can be droopy.  As new feathers grow, they passively push out the old feathers.  Sometimes the old feathers become loose, and can droop.  As a rule of thumb, juvenile feathers are weak, and need to be replaced soon.  Hawks often keep their juvenile feathers a year, because as they grow them more slowly they can attain more keratin, and be more durable in the longer time in the nest.

Molt of remiges usually starts at P1 and when it gets out to about P6 the secondaries start, usually at S1 and inward from there.  Most birds molt sequentially.  Then the tertials start, and the tail is last. Tail starts form the inside out, starting with R1 and working outward.  Woodpeckers are an exception, they molt R2-6 first, then molt R1 later, to facilitate feeding techniques.

Feather wear.  Dark parts wear more slowly.  Look at gulls. Early in the year the white tips are big, later by spring the white tips can become smaller.  Another example is least sandpiper.  Scapulars white and gray tips in the spring, but by fall look almost all dark. Starlings wear off the non-black feather tips to go into breeding plumage.

Early in fall migration, shorebirds, adults in worn plumage, juveniles have very fresh plumage.  Later adults look very fresh, and juveniles look more worn.  Western Sandpipers for example seen on our trip.

Easiest way to study molt is at your feeder, or at the park in ducks.  You can study the progression easily this way.

Molt can be suspended, often larger birds suspend their molt in the winter.

How can this help us in our field identification?  Presence of wing molt can be useful.  Absence is less useful.  Sometimes species can be IDed at some times of year by their molt.  Leaches vs. Band-rumped storm petrels off Carolina in summer.

Golden plovers in California.

Hammond’s flycatcher.  In fall Hammonds molt on breeding grounds or near.  So in fall a molted empid in the west is Hammonds.  All others molt later.

In Texas cliff vs. cave swallow.  Cliff molts in S Am.  Cave molts in N. Am.

In So Cal nighthawks in molt in the fall tells us it’s a lesser nighthawk. Common nighthawks don’t molt until wintering grounds.

Only jaeger that molts off CA is Pomerine.

Western Sandpipers molt off west coast, Least don’t molt until in S America.

Now refer to Ken’s cumulative table of shorebird molting.

Look at the two basic strategies for molt, N. Hemisphere and S. Hemisphere. This is where the birds winter.

Northern  Hemisphere Strategy:  partial to imcomplete preformative molts.  Don’t include remiges.  Rapid & early PB molt.  PA molt is well defined, and is on non-breeding grounds.  Think W. Sandpiper.

Southern Hemisphere Strategy: Incomplete to complete preformative, remiges eccentrically or completely molted.  In PF many shorebirds have eccentric wing molts. Usually involved P9 & P10.   Note more molting in the long distance primaries, those which are more exposed at rest.   Protracted PB molts. May start body, and even wing molt on the nest or in early migration, usually on the wintering grounds Jan – April.   PA molt often overlaps with shedding of remiges.  PA molt can overlap with PB, more often PA molt happens at molt sites on the way to breeding grounds.

Over-summering:  relates to body size, migration distance.  Larger birds and longer distance migrants tend to over-summer in the first year.

Snowy plovers molt in N A.

Articles to check out:


Migrants,  Mono Lake,  Monsoons, and Molt


All You Ever Wanted to Know About Molt But Were Afraid to Ask Part II: Finding Order Amid the Chaos


A Tale of Two Strategies: Fall Molt of Adult Dowitchers


Active Flight Feather Molt In MIgrating North American Raptors


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