Individual and Group Variances in Rural vs Urban Settings

Abstract

The goal of this study is to determine the average group size of the American crow (Corvus brachyrhynchos). It is a well-known fact that crows are social and intelligent creatures. It could even be said that the intelligence of Corvids is comparable to that of many primates. The American crow is found in mostly rural, but also urban areas throughout the country. Crows are sometimes seen in large, raucous groups. Even though that might be when they are most often noticed they are also found individually and in much smaller groups as well.

To conduct the study, two locations were used to observe crows. One setting is a Wildlife Management Area and the other a park, both just outside of Russellville Arkansas. Individuals, groups of two-five, and six or more were recorded as well as the exact number in each group. Over the course of five observation periods 108 American crows were recorded. Contrary to my expectations there were far more crows found in an urban setting than rural.

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As for the group size the most often seen was between two and five which was hypothesized. The least often seen was groups with 6 or more. Despite groups of two-five being more common there were many more crows spotted in the groups of six or more.

Introduction

Often mammals, specifically primates, are considered the most intelligent animals, however studies have shown that Corvids are highly intelligent and social animals. There was even a study performed that suggests Corvids are able to infer mental states of other members of the same species.

This ability was only attributed to humans and other primates in the past. Crows, ravens, and jays are all included in this finding (Keefner 2016).

The population density of the American crow (Corvus brachyrhynchos) can vary significantly between rural and urban areas depending on several conditions. Higher densities are usually found in more rural areas, although this can mainly be attributed to reproduction and migration. Often in the winter crows will forage in groups in urban areas due to food availability (Ludwig et al 2009).

Crows can sometimes be found in large flocks, or murders. The social nature of these groups allows crows to share among each other knowledge useful for survival such as dangerous humans (Cornell et al 2011). The raucous nature of the large groups means that larger groups are most often what people think of when seeing crows. However, while crows are known as social animals the size of the groups they travel in often varies greatly, and they are even seen alone. The variance of group sizes, or whether they are more often not in groups at all is of particular interest. For my hypothesis I suspect that smaller groups of crows will be found more often than larger groups.

Study area

This study was conducted at Galla Creek WMA (Figure 1) and Old Post Park (Figure 2); both locations are within a few miles of Russellville Arkansas. I travelled to areas of each site multiple times and conducted a total of five observation periods. Galla Creek WMA is a mixture of forest and wetland. At Galla Creek I chose densely wooded areas on the edges of fields for observations, I sat in a hunting chair and wore camouflage to avoid startling the wildlife. Old Post Park is more urban than Galla Creek and receives human visitors in larger numbers. The crows at Old Post Park are used to humans and I was able to observe from either a bench or my vehicle.

Data collection

For both locations I recorded the groups of crows that I saw, lumping them together in the following group sizes: one, two-five, and six or more. I also recorded the number of crows seen in each group. Each survey lasted for approximately 1 hour and was conducted at non-specific times of the day. I brought a monocular to each site to survey crows at a farther distance than with the naked eye.

Data analysis

On the primary data a two sample t-test assuming unequal variances with an alpha value of 0.05 was used to determine the differences in the average group sizes. Each group was compared with both of the others. A single-factor ANOVA was performed to ascertain the differences in means between all of the groups. Microsoft Excel was used to perform both of the aforementioned tests.

Results

In the course of this study a total of 108 American crows were observed and recorded to determine the average group size they are found in. When encountering crows the most likely group to be seen is size two-five. Single crows follow closely behind, and six or more make up the least common group to be seen. (Figure 3). However, despite groups of one and two-five crows being more common, the amount of individuals seen in groups of six or more exceed the other two significantly in numbers (Table 2). Also the number of crows observed in the more urban Old Post Park was vastly greater than the number spotted in the rural Galla Creek WMA.

A study by Heinrich and Marzluff found that young ravens have a tendency to form large groups. They search out food sources and then gather all the younger ravens in an area about as large as a 48 kilometer radius (1995). I suspect that most of the groups of 6 or more crows I observed were young crows with no territory. They share useful knowledge among each other and food as well. This benefits all the individuals involve and increases their chances of survival (Cornell et al 2011). The single crows and groups of two to five were likely older crows and families. It is also possible that some of the single crows were young and had not joined a flock (murder) yet.

Nearly all of the crows were observed in Old Post Park, which is the more urban setting and has many more visitors. These results are entirely juxtaposed with the data of Mustafa et al who found a significantly higher number of House Sparrows and Crows in rural areas (2015). I suspect that the large number of crows in the Old Post area is due to several factors: while still near town it is densely wooded in areas, there are constant visitors who likely leave food scraps behind, and it is in very close proximity to the Arkansas River. It is possible that Old Post is the perfect hybrid of rural and urban for crows. It is also important to consider that one less observation period was performed at Galla Creek. The fact that both of the observation areas are so close to the Arkansas River makes it a distinct possibility that some of the subjects of study could have been American Fishing Crows or (Corvus assifragus).