Due to urbanization, obstacles are presented for many North American avifauna during winter migration. Identifying overlapping areas used by migratory birds during the winter non-breeding season should increase efficiency in targeting areas destined for conservation of migratory avifauna. We compiled the latitudes for three distinct species, the Brown Pelican, Bald Eagle, and Canada Goose, sampled during the 2017 Audubon Christmas Bird Count. We then conducted a one-way analysis of variance (ANOVA) to test if there is a significant difference in mean latitudinal dispersal among the three bird species. Although we concluded that there is no significant difference in the mean latitudinal dispersal of the three distinct species, the birds’ distinct lifestyles must be considered in further establishing areas to conserve as flyways and migratory havens. In the future, scientists should utilize more data, sampling more birds and over the course of a longer period of time, to identify geographic hotbeds of migratory avifauna activity in order to better conserve these species.
Introduction
Every winter during the non-breeding season, more than half of the 650 breeding birds in North America migrate south to exploit the abundant resources of warmer climates. (The Basics of Bird Migration) However, many of these bird species face hardships as they undergo winter migration. Due to increases in development, migration patterns are interrupted as birds encounter manmade obstacles, including skyscrapers, wind turbines, telephone poles, and electrical wires. (What Hazards Do Migrating Birds Face? You Can Help!) Over the past few decades, southern areas within the United States, where many of these birds migrate to, have experienced rapid urbanization, presenting anthropogenic obstacles to migration. (Urbanization and the Southern United States.) Analysis of the relationship between winter migration and geographic location prompted our research on avifaunal latitudinal ranges with respect to winter migration times.
Newton and Dale, in their research Bird Migration at Different Latitudes in Eastern North America, studied relationships between latitudinal dispersal and migration among avifauna in eastern North America, ultimately concluding that latitude is a reliable indicator of migratory location because latitude is an exceptional measure of variables, such as daylength and climate, that influence available resources and thus migration. (Newton and Dale 1996) Therefore, winter latitude serves as an indicator for areas used by migrating birds.
In this research, we sought to identify a relationship in latitudinal dispersal during this past winter’s (December 2017) migration among three unique bird species: the Brown Pelican, the Bald Eagle, and the Canada Goose. We were interested in targeting overlaps in latitudinal ranges among the three bird species in regards to conservation of migratory grounds. We therefore examined the relationships among mean latitudinal dispersal of the three bird species.
Targeting an area that several birds’ non-breeding grounds overlap may increase efficiency in establishing areas to preserve as havens for migratory North American avifauna.
Methods
Every Christmas Day in the United States, thousands of ornithologists survey bird species within their respective geographic locations. These scientists upload their data to the Audubon Christmas Bird Count (CBC), a platform in which other users can derive data on the sampled avifauna. Using the CBC, we collected all data on the Brown Pelican, Bald Eagle, and Canada Goose from December 25th, 2017. For this day, ornithologists from various locations within the US counted 1890 Bald Eagles, 1702 Canada Geese, and 194 Brown Pelicans.
Using Microsoft Excel, we compiled the latitudes of the locations in which the birds were sampled on the CBC. Then, we conducted a one-way analysis of variance (ANOVA) to analyze mean latitudes among Brown Pelicans, Bald Eagles, and Canada Geese. The ANOVA yielded a p-value greater than 0.05 (see Table 1), resulting in failure to reject the null hypothesis. Therefore, we concluded that there is no significant difference in mean latitudinal distribution of the three bird species.
Results
Table 1. Analysis of Variance (ANOVA) summary of comparison of mean latitudes between Bald Eagles, Brown Pelicans, and Canada Geese shows no significant statistical difference. Mean latitudes of the Brown Pelican, Canada Goose, and Bald Eagle were derived from the Audubon Christmas Bird Count on December 25th, 2017. The three bird species served as treatments during the ANOVA. 1890 Bald Eagles, 1702 Canada Geese, and 194 Brown Pelicans were sampled during the 2017 count. Based on a p-value of greater than 0.05, we failed to reject the null hypothesis and concluded there is no significant difference in mean latitude among the three bird species.
Figure 2. Mean latitudes among the Bald Eagle, Brown Pelican, and Canada Goose illustrate lack of significant difference. H. leucocephalus, P. occidentalis, and B. canadensis, are the latin nomenclatures, respectively, for the Bald Eagle, Brown Pelican, and Canada Goose. Mean latitudes for the Bald Eagle, Brown Pelican, and Canada Goose were respectively 41.3698928, 28.08964175, and 40.8997624. Error bars were derived from standard deviation of the latitudes. Standard deviations for latitudes of the Bald Eagle, Brown Pelican, and Canada Goose were respectively 5.846658777, 7.121359317, and 4.672848453.
The approximate mean latitudes for all sampled Brown Pelicans, Bald Eagles, and Canada Geese was respectively 28.1, 41.4, and 40.9. (Figure 1) Because the one-way ANOVA yielded a p-value greater than 0.05, we failed to reject the null hypothesis. (Table 1) We therefore concluded that there is no significant difference in the mean latitudinal dispersal among the Brown Pelican, Bald Eagle, and Canada Goose.
Discussion
Because there is no significant difference among the mean latitudinal distributions of the three bird species, it seems that they should occupy similar latitudinal ranges and thus environments. Nevertheless, the mean latitudes of the Bald Eagles and Canada Geese were approximately 13 degrees greater than the mean latitude of the Brown Pelican (Table 1). It initially seemed odd that there was no statistically significant difference in mean latitudes among the species. Nevertheless, the lack of significant difference is likely attributable to the relatively small sample size of the Brown Pelican (194) compared to the Bald Eagle (1890) and the Canada Goose (1702). Increased standard error as a result of the small samples size may have resulted in lack of statistically significant differences in mean latitude.
More importantly, although the three bird species do not occupy a statistically different mean latitude during the winter, it is important to first note the limitations of this research. Firstly, we only used data from 2017 and it is possible that the data from this past CBC is an anomaly compared to the historical data. Furthermore, the skills and experience of the ornithologists who participate in the CBC vary, so it is possible that amateurs mistook some of the birds for others, although this is of lesser concern. In addition, the count takes place only on Christmas Day and in areas inhabited by the ornithologists. The Audubon Christmas Bird Count solely takes place in the United States, despite all three birds migrating to countries that are of lower latitudes than the United States, such as Mexico. This is especially problematic for the Brown Pelican, whose winter migration extends as far south as Guatemala. (Brown Pelican) Thus, the count is limited by both time and space as a result of ornithologists’ geographic distributions and CBC timing. Scientists in the future may decide to consider the distribution of ornithologists and respective sampling sites to determine the efficacy of the CBC.
The three birds occupy distinct environments and exploit distinct resources. Canada Geese occupy habitats near freshwater bodies, grasslands, and grain fields, where they feed on sedges and grasses. (Canada Goose Life History) The carnivorous Bald Eagle feeds on other birds, reptiles, invertebrates, amphibians, and mammals in coniferous and deciduous forests. (Bald Eagle Life History) On the other hand, the Brown Pelican feeds on small schooling fish in shallow marine and estuarine environments along the coastlines. (Brown Pelican Life History) Although there is no statistical difference in mean latitudinal ranges, the unique lifestyle of the Brown Pelican is testament to the lower latitudinal range, which encompasses coastal habitats extending from the United States to Guatemala. Brown Pelicans, as marine avifauna, occupy a highly different ecological niche than the Bald Eagle and Canada Goose, resulting in latitudes that reflect this marine lifestyle.
Despite the limitations of this research, the results are nonetheless important in determining migratory ranges of three distinct avifauna within the United States. In the US, the mean winter latitude of the Bald Eagle and Canada Goose extend across Northern California, Nebraska and Pennsylvania, while the mean winter latitude of the Brown Pelican extends across Southern Texas and Central Florida.
By identifying overlapping winter latitudinal ranges of various species, scientists may efficiently identify areas to be preserved as migratory grounds and flyways. (Data Zone) Habitat loss due to urbanization imposes great threats to flyways and non-breeding grounds, which are indicated by winter distributions. By accurately identifying mean latitudinal distributions of several bird species, scientists may be able to identify the most efficient methods of preserving these grounds and constructing flyways that connect the summer breeding grounds to the winter non-breeding grounds. In the future, scientists should utilize more data from more bird species in more countries, and over the course of a longer period of time, to identify the most efficient means of preserving land destined for North American avifauna migration.