Wings identify the sex of birds
Migratory bird reproduction is important to sustain populations.
Reproduction is dependent upon the relative number of male and
female birds in the population. A sex ratio is the average number of male birds
for every female bird. We use sex ratios to understand a species' capacity for reproduction.
Wings and tail feathers identify the age of birds
If we identify a lot of immature birds, then we know that
many adult birds are successfully reproducing. We can estimate
reproduction rates from the ratio of the harvest of immature birds
to adult birds. However, since immature birds are more vulnerable,
we use banded bird recovery data to "correct" for the greater
number of immature birds that are harvested when calculating the
proportion of immature birds in the population.
In the graph below, you can compare different species' age
ratios by year.
Some years, when bird populations are
high, harvest is high and vice versa. Managers are more concerned
about harvest rate than total harvest. Harvest rate is the
proportion of a species' total population that is harvested. We
calculate harvest rates from bird banding data.
US Fish and Wildlife Service Division of Migratory Bird Management
Web content created by Emma Chan and Abby Walter