Urbanization is one of the leading causes of species
endangerment and most urban ecology studies focus on the species that
don't do well in cities and towns. However, there are some species that
do very well in urban environments - the urban 'winners'. I am interested
in determining what factors in urban areas allow these species to become
so abundant. To address this I am comparing urban and non-urban
populations of the Northern Mockingbird (Mimus polyglottos). I am
specifically testing the following two hypotheses:
1. Mockingbirds are abundant in
urban areas because there are more food resources
2. Mockingbirds are abundant in
urban areas because nest predation rates are lower.
Data from the 2005 and 2006 breeding
seasons indicated that nest predation rates were lower in urban areas
relative to non-urban areas. However, in 2007 and 2008 there were no
differences in predation rates between urban and non-urban populations.
We will be continuing to collect data on nest predation rates this year
and we will be placing video cameras on nests to determine the identity
of the predators.
What we do:
- First, we look in bushes and trees for mockingbird nests.
- When we locate a nest we check what's in there every 3 days.
We write down how many eggs and/or nestlings there are, describe
what the nestlings look like, and weigh the eggs/nestlings. With
this information we can determine clutch sizes, the percentage of
eggs that hatch, the number of nestlings that survive to leave the
nest (fledge), and predation rates on the nests.
We also catch the adult birds, weigh them, put leg bands on
them, and then release them. This gives us information on
survival and movement of individuals. To catch the adults we use
mist nets near their nests that they fly into and get trapped.
This does not harm the birds!
A large part of the study this year will be to determine who
the nest predators are. We know that a whole list of different
things will eat mockingbird eggs and nestlings (crows, blue jays,
grackles, raccoons, snakes, cats, rats, hawks, etc), but we don't
know how frequently any of these are actually depredating (eating)
the nest contents. To figure this out we are placing video
cameras on the nests to catch them red-handed! See the video
clips page for some videos from last year.
Last year we tried a food supplmentation experiment.
We placed suet feeders in the territories of half the urban pairs
and half the non-urban pairs. We wanted to compare how the urban
versus non-urban birds responded to additional food in urban
versus non-urban locations. We were plannning on measuring how
many eggs they laid, how much the eggs and nestlings weighed, etc.
Unfortunately, none of the non-urban birds would eat from the
feeders, so the experiment did not work! Why do you think only
the urban birds would eat from our feeders?
Last year we started a new project on mockingbird songs. We
want to know if mockingbirds in the city sing differently than
mockingbirds in the country. Other researchers have found that
city birds sing at a higher pitch to overcome their noisy
environment. However, these studies have been done with species
that don't mimic sounds in their environment like mockingbirds do.
To do this we'll be walking around with recording equipment
(parabolic dish, microphone, and recorder) and recording males
Four mockingbird eggs
Three mockingbird nestlings that just
hatched and one egg that hasn't hatched yet.
|It's hard work keeping the cows away
from our mist nets