First, we wanted to understand how the states compare with each other based on the climatic factors that we have, as well as getting a general idea as to how the Song Sparrow sightings have changed over time. We categorized each state in the following manner:
Song Sparrow population is on different scales across the four states that we selected, as can be seen in the above plot. To visualize how many of the total sightings were from each state, we created a stacked bar graph that included total sightings per state from 1981-2010. Over the thirty years, there were a total 184,070 sightings across the four states. Wyoming sees the least Song Sparrows statewide, only accounting for roughly 2.2% of the total sightings. Wisconsin on the other hand sees the most, accounting for about 43% of all sightings from 1981-2010. These sightings differ because of environmental factors that are unique to each of these four states. We then looked at yearly temperature, precipitation, and drought index data to get a better idea of what specific factors play a role in Song Sparrow population.
Wisconsin sees a relatively high amount of Song Sparrows per year. However, there is a clear drop off in the early 2000's that is likely due to the U.S. drought of 2002, which is highlighted on the PDSI plot. Between 1995 and 2003, there was roughly a 1.3% decrease in bird sightings per route. Since then, sightings have been increasing again by about 1 sighting per route. It's also interesting to note that during a harsh cold wave in the late 90's, Song Sparrow sightings were at their peak. Wisconsin has experienced very little variation in climate in the past 15 years, and such the regression graphs dont show much of a strong positive or negative correlation towards Song Sparrow population. What if we look at a different climatic zone that experiences harsher summers?
California's Song Sparrow sightings have been more chaotic than Wisconsin. This could be due to a few factors, but the main one probably being that a large state like california experiences a much wider range of climates than Wisconsin does. It experiences a mediterranean climate with dry summers and wet winters, and it also is home to a few deserts, which is not seen in any of the other three states. California is also known to struggle moreso with droughts than states outside of the southwest. Between 1981-2010, it experienced three droughts, two of which severely affected song sparrow population. During the drought of 1983 and 1984, California saw a PDSI decrese of almost 8, which is a massive change on a scale with a range of only 20. During this time, song sparrow sightings went down about 4 per route. The drought of '02, which we saw affected Wisconsin's song sparrows, caused a similar drop off in sightings in California. In 2001, sightings per route reached its peak of 14 per route, but dropped down below 10 by 2004. This number however quickly rose again to 14 by 2010. California's extreme climates make it hard to discern which environmental factor affects Song Sparrows the most. The largest slope between the three regression lines for California was temperature's at 0.144, but for the most part it seems that Song Sparrow population has found a balance over these 30 years. California's wide range of precipitation values contributes to the small slope value of 0.061 of the respective regression line. This leads us to believe that due to little change in sightings over such a wide range, precipitation is not the leading factor that contributes to Song Sparrow population. Do other western states expereince this level of variability in Song Sparrow sightings?
Wyoming sees the least amount of Song Sparrows out of the four states we analyzed. A possible reason for this is the presence of the rocky mountains which might make bird migration more strenuous. Due to the low numbers of sightings, we decided to sacrifice the Wyoming regression lines to meet the 10 plot requirement. Also unlike California, Wisconsin, and New York, bodies of water are not present nearby, making it more difficult for birds to hydrate and sustain life. Wyoming also sees the least amount of precipitation over this 30 year period only reaching a maximum of 20 inches in a year. It is also the coldest state of the four, with an average yearly temperature of a little over 40 degrees Fahrenheit. Wyoming's data is a little hard to interpret, as their sparrow population is much lower than the rest. The most significant event that factored into Song Sparrow population was again the drought of 1983-84, which saw sightings per route reach its 30 year minimum of 3. For the most significant data, we must turn to a state with a much higher abundance of Song Sparrows.
New York and Wisconsin see a ery similar amount of Song Sparrows over this 30 year period (77,354 vs 79,864 respectively). New York saw a decrease in sightings after a drought from 1988-89, but unlike Wisconsin, their population didn't recover as well. Sightings dropped by 10 per route in a four year period and never surpassed 33 sightings per route after its peak of 40 in 1990. The slope on the temperature regression graph of -0.371 indicates that climate change has impacted Song Sparrow population, at least in New York. Greater precipitation could potentially be limiting flight visibility of Song Sparrows, and thus hindering their movement and causing them to seek homes elsewhere, as indicated by a slope of -0.196 for the preciptitaion regression line and -0.742 for the PDSI regression line. There is also a clear outlier on all three graphs that recorded a little over 40 sightings of the Song Sparrow at that route. This could be due to a high-alert, over-enthusiastic bird-watcher who noticed more Song Sparrows than most others that were overseeing other routes. Without this data point, the slope values for all three regression lines would be even further from zero, making the relationships even more harsh. Due to the large slopes compared to other states, and the visible drop in number of sightings as seen in the line graph at the top of the page, we decided to take a closer look at New York's changing Song Sparrow population.
This animation not only shows how Song Sparrow sightings have changed over time, but also their geographic distribution across the state of New York. It's clear that Song Sparrows prefer upstate and rural New York to the urban parts like New York City and almost all of Long Island. Analyzing the distribution across space over time, it appears that most sightings occur in the western half of the state. NYC is also on the Atlantic Ocean and Song Sparrows tend to shy away from oceanic coasts. Between the years of 1987 and 1991, there were two sharp decreases in PDSI that were followed by a drop in Song Sparrow sightings, and though the drought was followed by a period of wetter climate, Song Sparrow population was unable to recover due to reocurring droughts in the early 2000s. This is potentially due to the increased risk of storms related to being close to a large body of water as well as their inability to fly long distances. The animation shows clearly how Song Sparrow sightings decreased per route. In 1990, shortly after the drought, sightings per route was at 41. Up through 2010, it never emerged outside of the low 30s, even reaching as low as 29 in 2000. We find New York Song Sparrow population has suffered dramatically due to a frequent reocurrence of droughts through the combined effect of lower preciptation levels and higher temperatures.
We sought to determine what, if any, were the main climatic factors in changing Song Sparrow populations across different areas of the United States. By evaluating temperature, precipation, and droughts, we looked at the states Wisconsin, California, Wyoming, and New York, as well as the recorded number of sightings of Song Sparrows by the North American Breeding Bird Survery. This study would also like to note that there are a number of subspecies of the Song Sparrow that were not differentiated between. As a result, Song Sparrow became a sort of umbrella term that encapsulates all these subspecies. What we found was that while climatic factors affected Song Sparrow populations differently in each state, the frequency of extreme events, specifically droughts, seems to play the largest role in affecting Song Sparrow populations. To get a more concise answer as to what distinct factors affect Song Sparrow population, this study suggests the evaluation of Song Sparrows across the entire United States as well as looking at a multitude of other envirnomental factors. We were unable to test this due to computational limitations and time restraints. Overall, it's important that we take care of our environment to the best of our ability to ensure that specie diversity is maintained, if not strengthened.