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Category: Birding at the Chico
 
Posted by Bill M. on 09/18/2017

How to I.D. and Age An Orange-crowned Warbler
Category: Birding at the Chico
This adult (orange crown feathers visible after blowing on the top of the head) Orange-crowned Warbler appears to be reading the IDENTIFICATION GUIDE TO NORTH AMERICA BIRDS Vol. 1 by Peter Pyle, the bird-banders bible. The book tells bird banders what to look at and what to measure in order to age a bird and how to separate it from look alike species. It also suggests one or two band sizes that should fit the leg of the species. 

 ORANGE-CROWNED                                                               OCWA
Vermivora celata                                                                           Species # 6460
                                                                                                       Band size: 0-0A

Species--From Tennessee Warbler (which see for separation from Phylloscopus warblers) by tl long (42-53; see Age/Sex); longest p - longest s 8-15 mm; upperparts olive to yellowish; distinct eye ring absent. Eastern birds from Mourning Warbler by much smaller size (wg 51-66, tl 42-53; see Age/Sex); undertail covs usually brighter yellow than the belly; legs blackish.

tl = tail, p = primary, s= secondaries, wg = wing, covs = coverts

The book then goes on to describe the different Orange-crowned Warbler subspecies, what to look at to determine molt limits, what to look at after wetting the top of the head feathers to see if the skull is ossified partially (this year's birds) or completely (birds older than one year), and then tells the bander what to look for on a bird to determine its age and what to look at to determine its sex
Posted by Bill M. on 09/15/2017

Sexual Dimorphism
Category: Birding at the Chico
 Outside the breeding season, many of Chico Basin Ranch's male and female mammals look similar.  For example, male and female spotted ground squirrels look identical to the untrained eye. However, in many bird species the plumage differences between males and females is striking. Think ducks and game birds. Taking this a step further, it makes sense for all ground nesting birds, where females perform the majority of egg incubation duties, for the female to be dull brown in order to avoid detection by predators.  

Blue Grosbeaks, a fairly common breeder where there are dense trees or shrubs on the Chico, is a good example of sexual dimorphism in birds.  First, look at the beaks for identification purposes and you can see why the French name gros meaning large is a good name to describe the size of this grosbeak species' bill. As expected, the female (right) has a dull brown plumage but the male is strikingly colored. (This bird is actually a month old male. Young birds need to be dull regardless of gender to avoid detection. After a molt, he replaces his brown feathers with the bright blue ones) There is a reason. During the mating season males compete for available females. Male bird songs say to females "look at me, I am hot" and if the females show any signs of interest for the singing male, he then strut his stuff, showing off his fabulous plumage, and sometimes flying in with a takeout grasshopper to the female.  Sometimes it all seems to work.
Posted by Bill M. on 09/13/2017

Then They Go And Change Their Plumage
Category: Birding at the Chico
 The poet, Ogden Nash, humorously wrote about how difficult it is to identify birds in his poem "Up From The Egg." He mentions that even after finally being able to identify a bird it changes its plumage writing..."then it goes and changes its plumage, which plunges you back to ignorant 'gloomage'..."  This is true but what he doesn't say is that juvenile birds take weeks, months and sometimes even a year to molt to adult plumage. I have shown in previous posts that some birds such as longspurs wear the tips of their feathers, not a true molt, resulting in a fresh and brightly colored breeding plumage whereas some birds suspend their molts until reaching their wintering grounds. These birds show a combination of adult and juvenile feathers if caught at the banding station.

Above is one of the most common migrant birds of the Chico, Chipping Sparrow.  In the fall many of the Chipping Sparrows caught and banded are juveniles and their plumage is different than it is when they become adults. At the left is an adult Chipping Sparrow as it looks in April and May. On the right is a juvenile bird as it appears in September and October. Making the identification even more difficult is the Chipping Sparrow genus, Spizella, has three other members passing through the Chico at varying ages and some of the juvenile birds are very difficult to identify.  Beginning birders sometimes ignore looking at sparrows and some may just call them LBJs, little brown jobs. 
Posted by Bill M. on 09/12/2017

   
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