Feathered Witnesses: Unravelling the Impact of Habitat Loss on Neotropical Avifauna with Stable Isotope Analysis

Introduction

The Tachyphoninae are a group of Neotropical lowland tanagers. As omnivores, and with a reasonable representation in the Zoological Museum of the University of Sao Paulo, they present an opportunity to use stable isotope methods to ask a number of questions relating to changes in habitat use and diet over time over their Brazilian range.

Like many places, Brazil has endured severe habitat loss over the last 500 years. Beginning with the arrival of the Portuguese in 1500, the introduction of sugar cane and other crops meant that many coastal forests were cleared. The expansion of cattle ranching and coffee plantations in the 17th and 18th centuries and the rubber boom of the next two centuries produced cleared more forests, especially in the Amazon. Finally, over the last seventy years, major infrastructure projects have increased urbanization, and further expansion of cattle and soybean agriculture westward has further contributed to the accelerated decline of pristine forests of all types.

Whilst we know the history of habitat loss in Brazil, the effects on the ecology of its avifauna are poorly known. The high diversity and endemism of Neotropical birds sensitize them to environmental change. Changes in their behavior and other natural history traits over time can give us insights into the effects of environmental shifts. By targeting four species of the Tachyphoninae, a group of common, non-migratory, Neotropical lowland passerines, we will elucidate how habitat loss has altered foraging behavior. We can extrapolate our findings to avifauna more generally and to future environmental change. This will help inform conservation strategies and priorities areas for protection.

Methods

The four species are Ramphocelus carbo (Silver-beaked tanager), Ramphocelus bresilia (Brazilian tanager), Tachyphonus rufus (White-lined tanager), and Tachyphonus coronatus (Ruby-crowned tanager). As well as being taxonomically similar, all are omnivorous, being largely frugivorous, but also feeding on seeds, nectar, and insects. The student will measure stable isotopes in the feathers and claws of these birds, all of these being well-represented from different years in the Zoological Museum of the University of Sao Paulo. Feathers are moulted annually principally between January and May. Date of collection and feather wear can be used to determine the year of moult in samples collected over the main moulting period. 

Stable isotopes of light elements (C, N and S) can be used in mixing models to calculate the importance of major, isotopically distinguishable, dietary items, for instance, the extent of omnivory. The species overlap only in Sao Paulo State, which has seen many land-use changes, so isotope metrics would determine if the species overlap their niches or partition them, and whether this has changed over time as the environment became fragmented. Conversely, comparing each species' isotope metrics between biomes will determine whether these niches endure throughout each species’ range. This data would detail empirically any changes in their ecology that have taken place in the later years of anthropogenic impact and allow a discussion of the extent of these changes in different biomes.

On a smaller scale, a comparison of sex/age would allow investigation of whether males and females and/or adults and juveniles have different patterns of diet/habitat use/niche? Further, whilst these are all considered generalist species, a comparison of isotopic niche width would reveal whether there has been some degree of individual specialization over time.

Training, skills and location

The student will be registered at the University of Glasgow and primarily based at SUERC, and thus join the training programme in the College of Science and Engineering, where they will be provided with skills that are essential to a researcher at all future stages of their career. The Stable Isotope Ecology Laboratory (SIEL) is equipped with state-of-the-art instrumentation for stable isotope analysis, and the student will be trained in practical stable isotope mass spectrometry, and the use of stable isotope metrics to elucidate variation in resource and habitat use.

They will also spend significant time at the University of São Paulo's Zoological Museum (MZUSP) collection, a treasure trove of biological diversity and a cornerstone of scientific research. It serves as a hub for biodiversity studies, providing a foundation for ecological, evolutionary, and conservation research in the Neotropical region. The collection of modern samples will necessitate fieldwork in São Paulo State.