When birds
are first hatched they only have one layer of bone making up their skull. Over the first couple of months to a year of
a bird’s life a second layer of bone will grow below the first layer. The second layer of bone usually follows one
of two patterns which can be seen in the photo below. Areas that only have the first layer of bone
will appear pinkish. The areas with two
layers will appear more whitish and will also have tiny white spots. The tiny white spots are columns between the
two layers of skull. When we skull we
squirt a little water to the back of the birds head and part the feathers to
create a window. Bird’s skin for the
most part is transparent which allows us to see through to the skull. We move the window around to look for
contrast between areas with two layer of bone versus the areas with only one
layer. If we find contrast this means
the skull is unossified and the bird is a hatch year. Fully ossified skulls will lack any contrast
and will appear completely whitish with tiny whiter spots. A bird with a fully ossified skull is not
necessarily an adult. Certain species
can have their skull become fully ossified by October and November. It’s always a good idea to combine multiple
characteristics when determining the age of birds.
The patterns of skull ossification |
NEW BIRDS
1 Eastern Phoebe
1 Eastern Phoebe
1 Ruby-crowned Kinglet
4 Hermit Thrush
4 Hermit Thrush
3 Gray catbird
66 Yellow-rumped Warbler
66 Yellow-rumped Warbler
2 Song Sparrow
RECAPTURES
3 Hermit Thrush
RECAPTURES
3 Hermit Thrush
6 Gray Catbird
6 Yellow-rumped Warbler
1 Swamp Sparrow
1 Northern Cardinal
BANDING STATS
# of New Birds: 77
# of Recaptures: 17
# of Species: 8
Effort: 140.3 net-hours
Capture Rate: 67.0 birds/100 net-hours
# of Nets: 23
BANDING STAFF
Aaron Given
Libby Natola
Matt Zak
Mattie VandenBoom
6 Yellow-rumped Warbler
1 Swamp Sparrow
1 Northern Cardinal
BANDING STATS
# of New Birds: 77
# of Recaptures: 17
# of Species: 8
Effort: 140.3 net-hours
Capture Rate: 67.0 birds/100 net-hours
# of Nets: 23
BANDING STAFF
Aaron Given
Libby Natola
Matt Zak
Mattie VandenBoom