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The Impact of Environmental Factors on Evolution of Avians

Emily Scott

Bio 112

Dr. Walkup

Abstract

During this semester, I was very interested in Charles Darwin and more specifically, his studies on the birds of the Galapagos Islands. Charles Darwin observed several different species of finches with unique beaks, each with different functions and beak shape, and determined that the finches had evolved to adapt to different food sources and environmental changes. In this paper, I will be discussing the over all evolution of birds and outlining Charles Darwin’s discovery of the finches in Galapagos, but also will document a lesser known bird, the Purple Martin, and their adaptation to their lack of housing structures. Throughout this paper, I will be explaining the reason for the avian species need to adapt and change, what caused it, how they adapted, and if that adaptation will change how the species behaves in the future.

Introduction

In 1835, Charles Darwin observed a group of about 15 species of finches, and discovered they all were considerably different in beak function and beak form. His discovery led to a new found wealth of information on the species around us, and how they came to be. This discovery paved the way for a new found understanding on how species were formed, and although his discovery was met with great criticism, we are now able to understand that birds and other species will continue to adapt and change when faced with environmental changes. The evolution of the avian species is not limited to the obvious display of evidence found in the Galapagos island, but still continues today in another species closer to home, the Purple Martin.

Charles Darwin and his Galapagos Discovery

In 1831, a British surveyorship, the Beagle, set off on a wordly voyage. On that ship, was Charles Darwin. By 1835, the Beagle and Charles Darwin had reached the Galapagos Islands. Once Darwin arrived, he first took notice of distinct differences in the giant tourtoises,

and the varying shells they possessed. There he was informed by an island resident that the giant tourtoises had varying shells depending on which island location they resided in, this sparked Charles Darwin to wonder if species acutally weren’t fixed for all time, but instead could slowly change and evolve over time. Through this curiosity, Darwin began to wonder how one species could turn into another. This thought incited an idea now known as natural selection, which illustrates that a species can survive environmental changes if they adapt to them. This is demonstrated in the 15 finches Darwin brought back from the Galapagos Islands. All of the finches were similar except for their beak size and shape, and feeding behaivior. Of the 15 observed finches, beak depth varied. For example, large birds with a deep beak depth were able to survive in drought like conditions due to the ability to dig deeper and crack larger seeds. This proved that a single species can give rise to another species if their environment has changed or if they have been threatened in some way, in order to adapt to their surroundings.

Evolution of Pre-Historic Birds

Avian creatures have been around for 165-150 million years ago, dating back to the Jurassic period. The discovery of specific fossils solidified the theory that their evolution came from theropod dinosaurs, small feathered dinosaurs. Its no secret as to what happened to the dinosaurs during that time, so how did these dinosaur era birds survive the nine mile wide

asteroid that doomed so many species 66 million years ago? The asteroid demolished three quarters of all life. The only birds that survived were ground dwelling birds, ancient relatives of ducks, chickens, etc., as most of the trees were obliterated due to global wide wildfires, a consequence of the asteroid. Following the asteroid, these ground dwelling birds had to drastically evolve, and adapt quickly to survive their new found environment, leading them to the development of what we classify as birds in modern day time.

Purple Martins

Purple Martins are the largest swallow in the United States. There wingspan can span up to 15 inches, and have a body length of 7-8 inches. Despite their size, the Purple Martins have undergone many environmental struggles, and have had to adapt tremendously to modern day society. While they have adapted, the adaptations they have made have not bemefitted their species. A wide spread-rumor known to bird watchers all around the world is that pre-contact Native Americans used to hang up hollowed out gourds for the Martins in an effort to drive away crows from their crops, and thus they became comfortable dwelling in structures instead of nesting like other birds. Purple Martins were thriving until the European colonization of America. Their habitat quickly diminished and non native species began being introduced. Over time, the Purple Martins found themselves dwelling in homes, emptied out woodpecker nests, and other “birdhouse” like structures. Purple Martins were soon facing the brink of extinction due to their unique nesting behaivior and competition from invasive species. Because Purple Martins are used to and have adapted to human interaction and contact, they are likely to not revert to traditional nesting habits other than human-provided bird housing. In this case, these

specific birds are quite the conundrum. They have had to adapt and evolve to humans, but yet their conservation relies upon human made structures.

Conclusion

https://www.sciencedirect.com/science/article/pii/S0960982215009458

http://www.conservationandsociety.org/article.asp?issn=0972-4923;year=2019;volume=17;issue=3;spage=227;epage=235;aulast=Jervis

https://www.allaboutbirds.org/guide/Purple_Martin/overview