Why do some, but not all, tropical birds migrate? A comparative study of diet breadth and fruit preference

W. Alice Boyle, Courtney J. Conway, Judith L Bronstein

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Annual migrations of birds profoundly influence terrestrial communities. However, few empirical studies examine why birds migrate, in part due to the difficulty of testing causal hypotheses in long-distance migration systems. Short-distance altitudinal migrations provide relatively tractable systems in which to test explanations for migration. Many past studies explain tropical altitudinal migration as a response to spatial and temporal variation in fruit availability. Yet this hypothesis fails to explain why some coexisting, closely-related frugivorous birds remain resident year-round. We take a mechanistic approach by proposing and evaluating two hypotheses (one based on competitive exclusion and the other based on differences in dietary specialization) to explain why some, but not all, tropical frugivores migrate. We tested predictions of these hypotheses by comparing diets, fruit preferences, and the relationships between diet and preference in closely-related pairs of migrant and resident species. Fecal samples and experimental choice trials revealed that sympatric migrants and residents differed in both their diets and fruit preferences. Migrants consumed a greater diversity of fruits and fewer arthropods than did their resident counterparts. Migrants also tended to have slightly stronger fruit preferences than residents. Most critically, diets of migrants more closely matched their preferences than did the diets of residents. These results suggest that migrants may be competitively superior foragers for fruit compared to residents (rather than vice versa), implying that current competitive interactions are unlikely to explain variation in migratory behavior among coexisting frugivores. We found some support for the dietary specialization hypothesis, propose refinements to the mechanism underlying this hypothesis, and discuss how dietary specialization might ultimately reflect past interspecific competition. We recommend that future studies quantify variation in nutritional content of tropical fruits, and determine whether frugivory is a consequence or a cause of migratory behaviour.

Original languageEnglish (US)
Pages (from-to)219-236
Number of pages18
JournalEvolutionary Ecology
Volume25
Issue number1
DOIs
StatePublished - 2011

Fingerprint

diet study techniques
comparative study
fruit
diet
bird
fruits
birds
migratory behavior
frugivores
frugivory
tropical and subtropical fruits
competitive exclusion
interspecific competition
hypothesis testing
temporal variation
spatial variation
arthropods
arthropod
testing
prediction

Keywords

  • Diet
  • Elevational gradient
  • Fruit preference
  • Interspecific competition
  • Nutrient limitation
  • Resource variability

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

Cite this

Why do some, but not all, tropical birds migrate? A comparative study of diet breadth and fruit preference. / Boyle, W. Alice; Conway, Courtney J.; Bronstein, Judith L.

In: Evolutionary Ecology, Vol. 25, No. 1, 2011, p. 219-236.

Research output: Contribution to journalArticle

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