PhD 2021, Wake Forest University
I collected data for my dissertation research on Isla Española in the Galápagos Archipelago, ~ 600 miles off the coast of Ecuador. Our lab, led by my adviser, Dr. David Anderson, has intimately studied the breeding behavior and ecology of a large seabird, the Nazca booby (Sula granti), since 1984, making this a very valuable long-term natural study.
Over the course of one season, we monitored daily more than 2,000 nests to collect information on the parents, egg lay date, hatch date, and chick survival. We put a uniquely-numbered metal band on the leg of all chicks to follow individuals over their whole lifespan, helping compile a long-term database on the birds’ breeding behavior. Nazca boobies experience actuarial senescence -- the probability of surviving to the next year decreases with advancing age. They also experience reproductive senescence, with older birds producing fewer chicks than younger birds. My research investigated foraging behavior as a proximate mechanism to explain the observed reproductive senescence in Nazca boobies. I used GPS, TDR (time-depth recorders), and accelerometers to identify where individual birds forage, how deep a bird dives, and how their foraging performance can change during a foraging trip. Specifically, I studied how environmental factors and individual factors (age and sex) affected foraging behavior.
Where does an animal forage?
We can figure that out with biologgers
The most exciting development in the field of foraging ecology is the advancement of biologgers, small pieces of technology that can be attached to animals without harming the animal. They can provide information about an animal’s behavior and even the environment that the animal moves through. For example, I can attach a GPS—the same technology as in your smart phone that lets you navigate with maps—that can give information on where a bird travels when it isn't on the nest. An accelerometer—similar to the one in your activity tracker that tells you how many steps you have taken today—can tell us when a bird flaps its wings and at what frequency. This technology has greatly increased what we know about how an animal forages, providing details on behaviors that take place where humans can’t observe them.
Does age influence a bird's flight performance?
Nazca boobies can live to 28 yrs
Studying aging effects in wild animals can be difficult because it requires following an individual across its lifespan. We know that in humans, athletic performance declines with age, and this decline is usually associated with decreased muscle strength and function. Research shows that greyhounds and horses show a similar racing performance decline; older individuals don’t run as fast as younger individuals. High foraging performance is critical for survival and raising young, but how does that change with age? In some species, foraging location differs between age groups or predatory behavior declines with age. I explored how Nazca booby flight performance — a critical aspect of foraging — changes with age. I tagged birds with GPS and accelerometer loggers in 2015 and 2016 and calculated metrics like how fast a bird flaps its wings and travels, and how much force the bird exerts during a wing flap. A surprising result: flapping traits measured from accelerometers varied by sex, but not by age. Read more in Ecology and Evolution.
How does foraging change with age and environment?
Maybe old birds perform fine when conditions are good, but bad in a "poor" environment
Seabirds, like the Nazca booby, can travel hundreds of kilometers in search of food. They prey primarily on fish and squid species and use cues from other animals (e.g., tuna) to alert them of prey. But we don’t have a firm understanding of how environmental variables, like sea surface temperature (SST), influence where a bird chooses to forage. Nazca boobies are visual predators, plunge-diving when they spot prey, so changes in cloud cover and therefore light intensity may affect their foraging success. While our earlier research showed limited evidence for aging in flight performance, we expanded the study to include a larger sample size and more years of environmental variation. I tagged >600 Nazca boobies with GPS loggers during five breeding seasons and tested how age and environment influenced their foraging effort (e.g., how far they travel) and foraging success (how much mass they gain from foraging).
Sleep in Nazca boobies?
We can look at posture in camera trap photos
Sleep is ubiquitous across many taxa, including elephants, humans, and jellyfish. While the functions of sleep remain unclear, sleep may function to reduce metabolism and decrease energy expenditure. However, sleep increases an animal’s risk to predation by making the animal immobile and limits an animal’s ability to forage for food. Nazca boobies can forage for multiple days and we are unsure how much an individual can rest on the water. Sleep after a foraging trip may be critical for a bird to recover and be a successful breeder. I have mentored three undergraduate students in their study of sleep in Nazca boobies. Our first goal was to identify if Nazca boobies sleep, and then ask questions about how sleep changes in individuals, depending on the age and sex of the bird.
Monitoring blue-footed boobies
Social media and community science can help
The blue-footed booby population in the Galápagos Islands has declined dramatically in recent decades, from an estimate of 20,000 individuals in the 1960's to approximately 6,400 birds in 2011. The decreased number of blue-footed boobies and lack of successful breeding was linked to a decline in the supply of their preferred food, sardines, which disappeared from the archipelago after 1997.
Our lab banded > 1,000 blue-footed boobies to monitor the population. Surveying birds by boat is expensive and logistically challenging, so we considered an alternative way to monitor the birds: social media. Tourists who visit the islands often post images of blue-footed boobies on Instagram, giving us the opportunity to identify banded birds. This initial study yielded some data, but mostly of one individual at a popular beach. With the help of Wake Forest University undergraduate Landis Pujol ('20), we launched the Blue-footed Booby Band Resight Project, a website where we can collect data on banded boobies. We encourage visitors to the islands to share photos of banded birds with us!