Posts Tagged ‘Molt’

I went out and did a bit of birding this morning around the wetlands along the shipping channels near where I live. It was a very pleasant morning. Still cool which is wonderful seeing as we are getting temperatures that are more and more in the 90s and 100s around here. I didn’t find anything unusual, but did have some really enjoyable sightings. In particular, I was treated to a flock of 17 Long-billed Dowitchers and 2 Spotted Sandpipers, all on their way north to their breeding grounds in the arctic. It was really cool to compare the individuals of each of these species. Most of the Long-billed Dowitchers were in their breeding plumage, which was looking bright, fresh and spectacular. A couple, however, still had a fair bit of the muted greys of their non-breeding plumage. The Spotted Sandpipers also showed a range of plumages, with one in full breeding plumage and one in full non-breeding plumage. Are these birds at different molt stages because of individual variation? Is it because some had an easier non-breeding season with lots of food and not much harsh weather, while others had a harder non-breeding season with less food and harsher weather like cold, wind, and rain? Might these differences in molt timing correlate with different arrival times on the breeding grounds and/or levels of success there? These kinds of carryover effects, as they are known, have always been of interest to me, but they tend to be quite challenging to study.

Other sightings of the morning included 3 Striped Skunks (one of which almost sprayed me and my dog!), Sacramento Cottontail, Red-winged Blackbird, Cooper’s Hawk, Green Heron, Gadwall, Cliff Swallow, Tree Swallow, several very pretty Song Sparrows, Ring-necked Pheasant, a Ring-necked Pheasant nest out in the midst of a wheat field that had been predated (by one of skunks, perhaps?), Belted Kingfisher, Great Egret, Great Blue Heron, House Finch, Killdeer, American Crow, Western Scrub Jay, Black Phoebe, Mallard, Canada Goose, European Starling, Morning Dove, American Avocet, American Coot, Bushtit, and a Pied-billed Grebe.

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Central California is awash with baby birds right now!  They are all over the place, out of the nest and following their parents around begging for food and learning what it is to be a bird.  All the young birds I have been seeing are in their hatch year plumage which means that they have the fully formed and functional feathers that they will keep until they molt next year (for most species, this first molt will take them into their adult plumage that they will then replace each year for the rest of their lives).  Just in the last few days in West Sacramento, I have been seeing young Western Scrub Jays, House Finches, American Crows, Bushtits, House Sparrows, Lesser Goldfinches, and Nuttall’s Woodpeckers.  Over the weekend in Berkeley, I saw a young Band-tailed Pigeon in its drab hatch year plumage following one of its parents, all be it a bit clumsily, to the bird feeders that my mom keeps.  The hatch year plumage of this species does not have the classic bronze feathers or white ring on the nap of the neck.  Young birds also lack the dramatic bright yellow bill and feet of the adults.  The population of this large and lovely pigeon species has been declining fairly quickly for unknown reasons, so to see that they are breeding in the Berkeley hills is especially exciting!  It will be very more exciting to see what young birds of other species show up around the area!

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Here in central California, most of the bird species are replacing the feathers that have been worn out during the breeding season.  The feathers that are falling out are being replaced by the feathers they will use to migrate to their non-breeding grounds.  This molt that they are going through is called the prebasic molt.  The general pattern that most birds have is a prebasic molt in the fall that leads to their basic plumage.  This is their simpler, duller, non-breeding plumage.  Basic.  When they are ready to return, they will go through a prealternate molt that will lead to their alternate plumage.  This is the bright showy plumage of the breeding season.  Not all species adhere to this pattern, but is a quite common one that is adopted by a lot of birds.  Different species have different details of the timing of their molts.  For example, the Yellow-billed Magpies have largely just finished their molt, while the Western Scrub Jays are in the middle of theirs.  How far a bird migrates, how it fared in the breeding season, if it had a single brood or had multiple broods, even how hard its spring migration or non-breeding season before may have been can all effect the timing of molt.

Molt is a significant endeavor to undertake twice a year.  The feathers of a bird can account for between 4% and 12% of a birds body mass, so it takes a large amount of energy and resources to replace them.  Mass for mass, this is equivalent to a human replacing all the tissue in their brain, liver, heart, lungs and skin!  But, replacing them is necessary.  As feathers age, they ware and break down.  This reduces their ability to keep a bird dry and temperature controlled.  It also causes a drop in flight efficiency.

Molt can also be used to determine a birds’ age.  Since feathers get more and more worn the longer they are retained by a bird, it is sometimes possible to see different feathers that have different amounts of ware side by side.  Depending on the pattern of where these feathers are, and how many different ‘generations’ of feathers are present, a trained eye can tell if a particular bird hatched this year, the year before, or the year before that!  So as you go out birding, pay attention to the feathers of the birds you see.  There are all kinds if details to be learned about their lives.

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