Cliff swallows and the extended phenotype








Some birds prefer to build nests in trees or simply nest in tree cavities. One species, in particular, prefers to build a nest out of mud on the side of an outhouse. Searching along the banks of a river for mud may sound like a dirty job. However, if you are a cliff swallow (Petrochelidon pyrrhonota), it’s simply a way of life. Cliff swallows find mud and gather it in their bills to use as the primary nest building material. The swallows bring the mud pellets back to the side of a cliff, cave, or even a man-made structure (in Yellowstone, they like outhouses) to construct a conical, gourd-shaped nest. What’s the point of collecting mud and other debris to construct an odd-looking nest? Why do cliff swallows prefer to build these types of nests in colonies? To begin to answer some of these questions, it is important to look at the reason(s) for having nests.

There is a huge amount of variation in nest design among animal taxa. Some mammals dig burrows, fish construct craters, and termites build mounds. Within the bird family, the there is still quite a variation. Even though the design is different, all nests basically serve as a place where animals lay eggs and/or raise their young. Why would cliff swallows go through all the trouble of building a gourd-shaped nest attached to the side of a building in close proximity to other nests (in a colony)? What is the role of natural and sexual selection in nest building? Do environmental factors influence construction?

Nests can certainly impact the fitness of individual birds. The greater the fitness of an individual, the greater the chances of surviving and reproducing. This is seen in several ways. First of all, the location of nests as well as the design of nests both contribute to predator avoidance. Also, building nests in a colony can increase social interactions which, in turn, can increase the chances of survival. These strategies show that natural selection exerts strong selective pressures on the design and placement of nests, but natural selection does not explain it all.


Changing heron behavior?

By Lindstedt and Gazaille

Last fall, we began a research project that involved studying the behavior of the Great Blue Heron and it’s nesting habitat. We have made several trips to what is known as “Heron Island” on Lake Norman. Our first objective was to record baseline data, which included counting the nests in each tree, measuring DBH of nesting trees, and measuring canopy coverage of nesting trees. We had discovered under each nest there were an abundance of skeletal remains. At first, we thought it was mainly prey animals that the heron parents provided to the hatchlings, but to our surprise the majority of these skeletal remains were of the hatchlings themselves. This provided us insight into the mortality rate of the hatchlings.

Heron take-off. Credit John Simmons

Heron take-off. Credit John Simmons

Another interesting observation we made were the adult herons in their foraging habitat around Lake Norman. We noticed that adult herons on Lake Norman do not have the ability to wade because of the lack of shallow shore lines. This is due to Lake Norman being a man-made lake. Has this feature changed the foraging behavior of this specific heron group on Lake Norman? The herons have adapted to this by standing on shoreline trees, piers, and docks to hunt either fish or small mammals on the shoreline. Our main objective is to attempt to understand these different adaptations that these specific herons have acquired in the Piedmont region of NC.

Bird diversity

By Monroe, Ellis, Dufresne *This is a follow-up to the previous post

Surprisingly, many bird species populate the Statesville, NC area. Currently we are taking an inventory of bird species along a section of a greenway trail. We are conducting a point count, which means we are traveling to four locations along our greenway transect. At each location, we identify every bird possible for 8 minutes and record the species and number. There are occasions where we are not able to count the exact number due to a flock of birds that are too large to count or because we are only hearing them and cannot see them. If this is the case, we try our best using Crnell software. We are counting the number of birds because we want to obtain enough information to compare bird diversity of this greenway section to bird diversity of Iredell County using eBird data and Christmas Bird count data.

One counting location

Bluebird box for monitoring

It is interesting to think about whether coyotes in the area have helped increase songbird diversity over recent years by depressing the populations of local mesopredators (i.e. raccoons, opossums, foxes). On the other hand, coyotes, being the top predator here, could have had a negative impact on the bird population because of direct predation. This theory of whether or not trophic cascades exist could be hard to test. However, it will be interesting to look for correlations between bird diversity before coyotes in Iredell County, NC and bird diversity after coyotes. I also am curious to see how much coyotes actually prey on bird eggs and fledglings.

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