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Why Nazca Boobies Struggle to Breed in Old Age: A New Study Unveils Answers

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Nazca Boobies and their Declining Breeding Ability: Insights from Foraging Behavior

Tracking with GPS Unveils Insights into Nazca Boobies’ Foraging Behavior

In a quest to comprehend the reasons behind the declining breeding ability of Nazca Boobies in old age, a groundbreaking study led by Wake Forest University Professor of Biology, David Anderson, has shed light on the matter by examining their foraging behavior and its changes with age and environmental conditions that impact their reproductive success.

Foraging routes for Nazca boobies during egg incubation
Foraging routes for Nazca boobies during egg incubation from the breeding colony at Punta Cevallos, Isla Española, shown by a yellow star at 1°23′ S, 89°37′ W. (a) Routes colored by Breeding Season (see Figure S6 for a multipanel display). (b) Kernel densities (see legend) of all locations, regardless of activity. The black box in B bounds the area where environmental variables were measured (Supplementary Material). Credit: Ecology and Evolution (2023). DOI: 10.1002/ece3.10138

Spying on Boobies: GPS Tracking Reveals their Food Quest

Lead author of the study, Jenny McKee, a former graduate student at Wake Forest, attached small GPS loggers to over 800 birds to track their movements at sea. After the birds returned from their foraging trips, which could last up to a week, the researchers retrieved the loggers and downloaded the GPS data to analyze their food-seeking routes.

“It was fascinating to be able to spy on their activities using these tiny GPS loggers,” McKee expressed. “Each time we connected the GPS to the computer and downloaded the data to see their tracks, it felt like unwrapping presents on Christmas morning. It provided us with a snapshot of what the birds encountered while they were away from the nest.”

Decades of Research Reveal Surprising Insights

This study marks the latest contribution to the extensive research conducted by Anderson, who has studied various seabird species, including Waved Albatrosses, Blue-footed Boobies, and Nazca Boobies. For almost 40 years, Anderson and his team have been banding Nazca Boobies on Isla Española, a roughly 37-square-mile Galápagos Island.

The foraging performance of boobies was greatly influenced by environmental conditions, specifically the sea surface temperature of the Pacific Ocean where they search for food. When the water was warm, such as during the 2015-16 El Niño event, the boobies traveled shorter distances and spent less time actively foraging, indicating that food was more accessible.

“This finding was surprising because we typically associate El Niño with adverse effects on seabirds,” McKee remarked. However, this result aligns with earlier research conducted by co-author Emily Tompkins, who discovered that boobies produced larger clutches under El Niño-like conditions, although chick survival rates declined later in the 7-8 month-long breeding season.

Aging and Foraging Decline: Implications for Breeding

The research findings also revealed a decrease in foraging capacity as birds age, specifically among female boobies. When comparing females aged 12 to females aged 24, which were the oldest birds included in the study, the research team noted that older females traveled an additional 140 miles and spent an extra 15 hours foraging compared to their middle-aged counterparts.

These findings suggest that the time-consuming foraging efforts of older females may contribute to their reduced breeding success in old age. When older females dedicate additional time to forage, their mates may be compelled to leave the nest in order to meet their own nutritional needs. Consequently, this exposes the eggs or chicks to potential predation from Galápagos mockingbirds or hawks.

However, the decades-long dataset collected from Nazca Boobies continues to uncover intriguing details about the aging process, which is a challenging endeavor in wild animals. Future GPS data collected during later stages of the breeding season or data examining the diving behavior of the birds may further illuminate the aging patterns of Nazca Boobies.

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