How to Read the Bird Breeding Survey (Red-Winged Blackbird Declination)
The Breeding Bird Survey is a survey that has recorded the number of birds along specifically placed bird routes in Canada (Pardieck, 2019). The data being recorded in this graph is of the Red-winged Blackbird. There are 50 stops on the route that the bird breeding survey records data on (Pardieck, 2019). Within the distance of 40 kilometers; the stops are spread 0.8 kilometres apart individually (Pardieck, 2019). Despite that the birds are observed every year by surveyors on route, there are also multiple routes run within each year (Pardieck, 2019). The number of routes can affect the data recorded for bird population since smaller samples can indicate a higher proportion of birds if a larger number of routes recorded the same number of birds. The main question the graph attempts to answer is the following: how does the change in Red-winged Blackbird population change over the years?
Figure 1: The graph represents the change in bird population with each point representing birds sighted per route at a given year. The line represents the slope being the overall change in birds per route over years.
There is a downwards linear slope illustrated by Figure 1. This trend means that there is a negative relationship between the birds per route and years. Despite there being a line of best fit, it is not completely linear. Thus, there is some variability to this dataset. That variability is indicated by R2. This coefficient defines the variability to the data recorded (due to sample size disproportionality). The coefficient is 0.6781. The slope of the graph is the change in birds surveyed per route over time. Since, the slope is --0.7721, (using the formula y = -0.7721x + 1604.4, or y = mx + b), the amount of birds surveyed per route has decreased (hence the negative trendline) by a large amount each year.
In conclusion, the long-term population trend of the Red-winged Blackbird is shown to be declining each year. We know that from the negative slope, and since -0.7721 is quite a relatively steep negative slope, it is an alarming decrease in population for these Red-winged Blackbirds.