2013 Fall

Human/Crow Commensalism?

Some local observations and a quick survey got us thinking about a possible link between increasing bird populations and urbanization. First of all, we have noticed from being outside conducting research the last four years, the crows have seemed to increase each year. Since this was just subjective “data,” we decided to do some investigating. The results of a quick poll of walkers at Mac Anderson Park supported our idea that crow populations have been on the rise. After discussing several ideas as to why this may be (i.e. more people = more trash/food = more crows), we decided to do more digging.

When human census data from 1960-2010 is compared to crow populations from Christmas Bird Count data during that same time frame, a strong positive correlation does exist (see Figures 1 and 2). The years are placed by the data points.

Figure 1 (click to enlarge)

Figure 2 (click to enlarge)

However, this does not necessarily mean anything. Maybe crows are increasing independently from humans. Maybe there have been increasing numbers of human observers during the Christmas Bird Count events. Maybe observers have accidentally counted fish crows and ravens instead of American crows. Maybe it is all just coincidence. Then again, maybe it’s not.

The San Jose Mercury News reported in 2012 that an explosion in crow population had taken place in urban and suburban areas around the bay. The article states that crows are in the midst of a population surge and territorial expansion that has been ongoing since the 1960’s. This may be the result of one or all of the following factors: 1) mild climate; 2) lack of predators; and 3) abundant food and nesting sites that humans have provided.

John Marzluff is one of the experts trying to figure out why crows are able to live close to humans. One particular study supports the hypothesis that crow populations tend to be the highest in urban areas. This study also showed that the diet of crows was different in urban areas compared to wild areas. For example, the dominant foods eaten by crows in Seattle, WA were human refuse (prepared meats, breads, and vegetables). Crows living in a wild area along the Olympic Peninsula tended to eat equal proportions of invertebrates and human refuse.

So, besides crows, do other birds seem to follow this trend of benefiting from a rising human population, or what we would call urbanization? Barred owls may follow the same path as the crows. Field research conducted in Charlotte, NC showed that Barred owls are thriving in the city. This study indicates that there may be at least 300 pairs of Barred owls within 10 miles of downtown Charlotte.

Are there more experiments that need to be done? Of course. The questions becomes how to set up those experiments. In the meantime, watch out for the crows.


Great Blue Herons

Great Blue Heron

This project proposes to study the nesting habitat of the Great blue heron (Ardea herodias) on Lake Norman. There is a specific island that has been identified by North Carolina Resource Commission as a blue heron nesting habitat. This island is commonly called “Heron Island” because of its diverse bird population. This island is protected under the Migratory Protection Laws. These laws prevent people from disturbing these birds and their habitat from April 1st to August 31st. The Blue Heron is listed by The North Carolina Natural Heritage Program as a vulnerable species in the Piedmont. This research will further knowledge of the Blue Heron population and possibly advance the conservation policies on “Heron Island.” Using observational and experimental research science we would like to determine what factors (i.e. species of tree, size of tree, water quality, canopy coverage) cause this gathering of the blue heron.

The following shows some video of herons as well as  some of the things that have been done for herons on Lake Norman:
Live heron nest
Charlotte Observer
Heron Island

Crow Behavior

One research group is currently researching and documenting crow behavior. The first question of this study is, “Do crows feel more comfortable eating in groups?” Students will observe groups of crows and individual crows as they are eating and measure how many times per minute an individual crow raises its head and scans (scanning rate). A high scanning rate would seem to indicate the birds are worried about potential predators. This group thinks that the larger the group, the less scanning that will be taking place.

The next question this group will be examining is, “Is there a positive correlation between crow population and human population in specific areas?” Census data from Iredell County, NC, and the United States will all be compared to crow population numbers from Audubon’s Christmas Bird Count data.

Crayfish Study Coming This Fall

By Casanova, Melvin, Sierra, and Smart
We will be studying the crayfish population and water quality of the creek along the Museum Road section of the Greenway. Our main focuses will be the health of the crayfish population and the correlation between their population density and the levels of pollution in the creek.

We will capture and study samples of crayfish in four different areas along the creek. We will use contraptions that we have created so we can safely and efficiently capture the crayfish and observe them well. There are four spots we will study; one at the bridge at the beginning, one about a quarter of a mile down, another one at the second bridge, and one further down from that.

We will compare the data from the different plots along the creek and will also study dissolved oxygen levels and temperatures of the water.