Jeff Podos -- Research Interests
"Feeding habits, social behavior, nesting, anatomy, plumage -- in any bird are all interconnected, each affects the others in various ways...One cannot fully understand any aspect of a bird's natural history in isolation; but the web is so complicated that it is difficult to know how to tackle it -- which thread to follow first. -- David Snow, The Web of Adaptation (1976)
Current work on Darwin's finches of the Galápagos Islands, Ecuador, aims to document
interconnections between behavior (feeding, singing), morphology (beaks, heads, body size), and evolutionary divergence.
Darwin's finches are a well-known example of adaptive radiation, in which a single
ancestral species gave rise to multiple and diverse descendent species.
The Darwin's finch radiation has featured, most famously, pronounced diversification
of beak form and function, represented at its extremes
by the thin probing beaks of warbler finches and the massive seed-crushing
beaks of large ground finches.
My field team and I -- including key collaborators Andrew Hendry, Sarah Huber, and Anthony Herrel-- have been exploring a number of questions about finch
behavior, morphology, and evolution, particularly for birds on the central Galápagos island of Santa Cruz. Some of our work focuses on relationships between beak morphological diversification, vocal proficieny and song structure. Interconnections
between beaks and vocal proficiency are predicted given recent evidence
that beak movements play a key role in song production. Video analysis of birds singing in the field has revealed that Darwin's finches, like other songbirds,
adjust beak gape in precise register with changes in song frequencies. Gape changes are thought to occur to help Darwin's finches and other songbirds to maintain
the pure-tonal quality of their songs as they vary in frequency. This observation leads to the prediction that birds adapted for greater crushing strength should suffer greater
constraints on vocal proficiency, because of mechanical tradeoffs between force and speed. Inter and intraspecific analysis of song structure in relation to beak morphology support this prediction.
We are also examining the potential impact of correlated evolution between beaks and song on the process of reproductive isolation. Song playback studies are being conducted to evaluate the impact of song variation on song function. We are also conducting observations of intraspecific mate choice, in order to assess possibilities of sympatric population divergence.
Other current field activities include (i) observational studies of feeding in relation to beak form and function; (ii) tests of bite force capacities; and (iii) documentation of variation in genetic, morphological, and vocal traits among birds on Santa Cruz Island. We are fortunate to receive generous support for this work from the National Science Foundation.
Check out the splash page for NSF's Division of Integrative Organismal Systems website. The photo shows one of our finches, JP1046, enjoying a Scutia berry.
Songbird songs are wonderfully diverse, not only across species but also within
species, populations, and individuals. The evolution of this diversity
is linked to the fact that most songbirds learn their songs. They require
exposure to song models during a critical phase in their first year of
life, and subsequently engage in a protracted period of motor development
before being able to produce crystallized song. Vocal features that
are shaped during learning will be retained over evolutionary time through
cultural transmission.
My colleagues and I are interested in understanding how proximate features of song
production and perception, as expressed during development, can shape patterns
of song learning and diversification. This work follows directly
from the pioneering studies of Peter Marler and Susan Peters in the 1970s
at Rockefeller University. One of our specific interests in song learning
is that it can provide a unique empirical window into the role of performance
in behavioral evolution, given songbirds' natural predisposition for producing
accurate copies of song models. An ongoing collaboration
with Steve Nowicki and Susan Peters of Duke University examines how the
coordination of beak and syrinx movements during development can both impose
constraints upon and provide opportunities for novel timing patterns in
song production. At UMass, David Lahti and I have designed a series of experiments, to begin in spring 2005, to study trill rate and tempo learning in hand-reared swamp sparrows.
Questions about vocal diversification are also addressed using quantitative
surveys of vocal diversity, using bioacoustic analyses. Ongoing work
focuses on performance-based tradeoffs between acoustic features in trilled
segments of sparrow songs. Local field work in the northeastern United
States provides complementary perspectives on song function and diversity.
Experimental and theoretical work on animal communication systems hinges on our knowledge
of patterns in natural systems. Only a small percentage of natural
communication systems, however, have been studied or even described.
Ongoing work, conducted largely in collaboration with researchers from
theInstituto Nacional de Pesquisas da Amazônia in Manaus, Brasil, aims to document
patterns of communication and ecology in poorly-known neotropical vertebrate taxa.
Recent taxa of interest include river dolphins, arboreal rats, electric
fishes, and birds. In collaboration with
Vera M. F. daSilva and Marcos Rossi-Santos, I have been looking at the
structure of the vocalizations of the two species of Amazon river dolphins,
Sotalia
fluviatilis (the tucuxi) and Inia geoffrensis (the boto).
Our analyses have revealed significant structural differences in the vocalizations
of these species, with Sotalia producing high-frequency stereotyped
whistles typical of their oceanic dolphin bretheren, and with
Inia
produces low-frequency, highly variable vocalizations. This pattern
suggests that the well-known whistles of oceanic dolphins, which are learned
and used in social interactions, evolved after their split in evolution
from river-dolphin-like ancestral stock. This finding raises questions
about geographic variation in vocal structure among dolphin populations,
which we hope to address in the near future. Another project, spearheaded by Cristina Cox Fernandes, has documented spatial variation in the richness and abundance of electric fishes (Gymnotiformes) across the Amazon river basin.
Vocal learning and evolution in
sparrows
Exploration of communication systems and ecology
of neotropical fauna