This post was contributed by Alex Di Giovanni, an incoming PhD student at George Mason University and a 2020 WOS Research Grant recipient.
I am fascinated by behavioral ecology — how and why birds do what they do. I recently graduated with my Master’s degree from Mike Ward’s lab at the University of Illinois, where I investigated how the embryos of several shrubland and grassland songbirds including Field Sparrows, Common Yellowthroats, Gray Catbirds, and Northern Cardinals develop inside their eggs. Songbirds face many different challenges during the breeding season and must make decisions to deal with these challenges, including where and when to nest, how many eggs to lay, and how to incubate their eggs efficiently.
Through the use of a relatively new technology, a ballistocardiogram, I was able to measure the heart rates of bird embryos in the field without having to open the eggs. The ballistocardiogram calculates the heart rate by measuring the minute movements of the egg as blood is pumped through the embryo’s body. Songbird embryos rely on warm temperatures to develop, and their parents must actively incubate the eggs. Therefore, I also recorded the temperatures at which parents kept their eggs within the nest. From these data, I was able to track and compare the development of embryos of many different species. Tracking these species allowed us to draw conclusions about the different parental strategies birds may use throughout the developmental period. We found that the way species develop in the egg may be related to their risk of predation and whether their nest is a cavity or open cup.
I noticed that at my study sites, there were a surprising number of nests with a leftover egg remaining after the other eggs had either hatched or even fledged. After some research, I found that the number of unhatched eggs that I observed were comparable to what had been seen in other studies (around 7 to 10%; see Koenig 1982). I was still curious as to why this would occur, considering the amount of effort and resources that parents invest in both laying and incubating their eggs. This led to a second focus for my thesis research, for which we investigated at what point in the developmental process egg failure was occurring. Overall, those eggs that failed to hatch usually ceased developing very early in the developmental process. While there are many reasons why an egg may fail to hatch (see Assersohn 2021), it’s important to continue to monitor these rates, especially with a changing climate.
I am extremely grateful for the support of the WOS, without which this research would not have been possible, especially during the early days of the COVID-19 pandemic in summer 2020. This award allowed my field crew and I to remain socially distant throughout the field season, enabling us to collect data that otherwise would have been impossible to collect alone. The final part of my study was on the impact that Brown-headed Cowbirds had on the development of parasitized host species’ young, and whether the development of cowbird young themselves varied with different parental host species — we are still working through these data and are excited to see where the results lead us. I’m also looking forward to working with cowbirds for my Ph.D. and investigating some of the decisions they make when choosing which nests to parasitize!