Deviation Factors in the Mississippi Flyway: Geographic Barriers and Ecological Quality
Total Page：16
File Type：pdf, Size：1020Kb
i DEVIATION FACTORS IN THE MISSISSIPPI FLYWAY: GEOGRAPHIC BARRIERS AND ECOLOGICAL QUALITY Ian A. Anderson A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 2020 Committee: Verner P. Bingman, Advisor Kevin Neves Daniel D. Wiegmann ii © 2020 Ian Alfred Anderson All Rights Reserved iii ABSTRACT Verner P. Bingman, Advisor Migrating passerines (Passeriformes) can travel thousands of kilometers to reach their summer and winter grounds, and while migrating, they encounter environmental barriers like mountains, deserts, and oceans, which force birds to decide whether to continue in the typical migratory direction or deviate around the barrier. Hundreds of species of migrants utilize the Mississippi Flyway, which may involve encountering the Great Lakes including the southwestern coast of Lake Erie. Gesicki et al. (2019) found that during Spring migration many migrants deviated westwards along the southern coast of Lake Erie instead of crossing the lake along their same heading. The goal of the current study was to determine whether migrants arriving at the Ohio coast of Lake Erie in the Fall, after crossing the lake, would similarly respond to the coastal features of Lake Erie’s Ohio coastline as they do in Spring. Specifically, would migrants display deviated flight directions with respect to the coastline at three observation sites as well as compared to the broad front direction of migration recorded by Doppler weather radar in Cleveland? This was determined by comparing individual flight directions recorded from three sites, Cedar Point, Ottawa, and Maumee Bay, as well as the nightly, broad front direction recorded at Cleveland. Across a number of analyses, no meaningful differences in migratory flight directions were observed across the three observation sites nor with respect to the broad front direction recorded by Doppler weather radar. Generally, migrants flew in a south-southwesterly direction irrespective of location. As a separate analysis, no differences were found in the flight directions of migrants when birds observed early in the iv night were compared against birds observed later in the night. In summary, and in contrast to the Spring (Gesicki et al, 2019), migrant songbirds reaching the southern coast of Lake Erie in Fall do not appear to respond to coastline features nor do they deviate from the broad front migratory direction. Collectively, the Spring and Fall data suggest that migrating birds are active decision makers, choosing to deviate when approaching an obstacle (Ohio-Lake Erie in the Spring), but in the absence of any obvious benefit to deviate (Ohio-Lake Erie in the Fall), they do not respond to the same topographical features so no significant differences from the broad front were found. v This manuscript is dedicated to my partner Maren and my family for their unwavering support. Additionally, immense thanks to Black Swamp Bird Observatory for putting up with an overexcited seven-year-old who just wanted to hold birds; thank you for opening me up to the wonders of the natural world. vi ACKNOWLEDGEMENTS I would like to express my immense thanks to Dr. Verner Bingman for taking in a graduate student switching to a new program and showing immense patience with me to help me expand my limited knowledge of migration sciences. Additionally, I would not have made it this far without the rest of my committee members, Dr. Dan Wiegmann for always being available for help and questions, Dr. Kevin Neves for being a pillar of support, and Dr. Andrew Gregory for his incredibly technical lens on how ecosystems fit together. Thanks for all my fellow graduate students for helping me through these difficult times but most especially to my partner Maren, and my family for always being there for me. vii TABLE OF CONTENTS Page INTRODUCTION…………………………………………………………………….….... 1 METHODS………………………………………………………………………….……… 6 Data Collection…………………………………………………………….……….. 6 Weather Surveillance Radar Data……………………………………………….…... 9 Data Analysis………………………………………………………………………... 9 RESULTS…………………………………………………………………………………… 11 Individual Bearings……….……………………………………………………….… 11 Nightly Mean Directions and Comparison to the Direction of Broad Front Movement…………………………………………………………… 12 Influence of Time of Night………..…………………………………………………. 15 DISCUSSION……………………………………………………………………...………… 16 REFERENCES………………………………………………………………………………. 25 viii LIST OF FIGURES Figure Page 1 Total observations for each site in the observed years………………………………. 6 2 Preferred axis of migration for all observed migrants comparing the early and late time periods of each year and measures of accuracy for each dataset………………………………………………………………………. 13 3 Mean preferred axis of migration for each night recorded and measures of accuracy for each dataset …………………………………………………………. 14 4 Preferred axis of migration for all observed migrants and for the Doppler broad axis for KCLE………………………………………………………………... 17 1 INTRODUCTION Birds migrate based on seasonal availability of resources and their migration paths are called flyways. The Mississippi Flyway is one of the largest in North America and has 325 migratory species that utilize it (Howard 2019) out of the 993 species of the continent (Gauger 2019). Migrants may travel potentially thousands of kilometers (Battley et al 2000) before reaching the Mississippi Flyway as they migrate from South America to Canada, and during this journey they have to make decisions on how to approach obstacles they face. Many obstacles, like oceans or deserts, represent danger to migrants due to their lack of places to stop, rest, or feed (Biebach 1990). These obstacles represent a choice to each individual migrant: do they fly around it or go straight through? Migrants are forced to make a cost-benefit decision as one path is faster but more dangerous while the other is slower but safer. When travelling directly, migrants face higher mortality risk due to not being able to find refuge in inclement weather and a lack of available food sources (Lowery 1945). However, overcoming these obstacles allows for migrants to reach breeding grounds earlier than their cautious counterparts, resulting in fitness benefits for the risk-takers (Velmala et al 2015). Migrating earlier in the Fall allows for first year migrants to begin their gonadal maturation rate sooner which allows for easier nutrient acquisition before the Spring migration (Wingfield, 1990). The cost-benefit challenges described above are observed in the migration paths of many bird species in the world. Migrating Brent Geese (Branta bernicla) detour from the northern coast of Russia towards Scandinavia and then other regions of northern Europe, rather than simply flying a straight path over the Kara and Barents Sea which would be a shorter trip (Alerstam 2001). Red-backed shrikes (Lanius collurio) migrate from southeastern France to Tanzania, by flying along the eastern Mediterranean coast to avoid crossing the potentially 2 dangerous Sahara (Zink 1987, as cited in Alerstam 2001). Both of these migrant species seemingly have made the active decision to not take the shortest path to their destination in favor of their safety. Most migrants do respond to obstacles, but the responses differ based on the type of barrier (desert, water, etc.), the type of bird flight (soaring or flapping migration), and the energy reserves of the migrant (Guglielmo 2018). When migrating over large bodies of water, such as the Gulf of Mexico or the Great Lakes, birds can drift from their preferred path due to lack of topographical features with which to reorient themselves (Alerstam and Petersson 1977). When small songbirds drift over water, there is an increase in the energetic expenditure of migration, which may reduce migrants’ ability to adapt to future challenges (Nilsson 2019). Passerines often migrate along a coastline and later reorient before flying to suitable stopover areas as a method to compensate for drift; they sometimes even reverse their normal flight path to do so (Alerstam 1978). Deviations along ocean coastlines are widely observed, like the Mediterranean coasts of Spain and France in Bruderer and Liecthi (1998), but how inland bodies of water may affect migrants is much less researched. The Great Lakes are near the start of the Mississippi Flyway during Fall migration, and nightly migrant traffic was found to be decreased over Lake Erie in the Spring when compared to the land migration around it (Diehl et al., 2003) suggesting that migrants have a reason to not journey over this barrier. Increased mortality risk due to inclement weather, storms, and flight inefficiency due to drift can all be possible explanations for migrants choosing not to migrate over the Great Lakes (Diehl et al 2014, Newton 2007, Nilsson 2019). Migrants can take different paths when approaching the obstacle of Lake Erie, and Gesicki et al. (2019) found that during Spring migration, as many as 62% of birds deviated along the coast of Lake Erie instead of immediately crossing. The findings of the study suggested that 3 migrants chose to cross the narrowest width of the lake and over islands present. While Gesicki et al. (2019) looked at these migration trends in the Spring, using the archived data, similar questions will be examined in the context Fall migration. Migrants usually rest before crossing large barriers (Deppe, 2015) like Lake Erie and Fall birds would have already crossed this barrier. Migrants’ energetic states are