Sexual Dimorphism and Sex Ratios in Magnificent Frigatebirds

Sarah Trefry

Ph.D. Candidate

Department of Biology

University of New Brunswick, Fredericton

s.trefry@unb.ca
506-452-6033

Several distinct morphological and behavioural characteristics set Magnificent Frigatebirds (Fregata magnificens) apart from other seabirds, presenting an exciting opportunity to test hypotheses about their ecology and evolution. The most notable features that distinguish frigatebirds from other seabirds are the extreme differences between sexes; females are larger while males are more ornate, and sport a bright red inflatable throat sac when breeding.

Photo: A. W. Diamond

The behaviour of males is also unique; they display communally to females flying overhead, and abandon the female and young before the chick becomes independent. While Magnificent Frigatebirds are considered one of the most threatened species in the West Indies, large gaps remain in our knowledge of their ecology, including the timing of their breeding cycle, where they go in the non-breeding season, information on their moult ecology, and where they feed. The proposed research, designed to fill in some of these gaps, is to take place on Barbuda Island, in the Lesser Antilles.

This project presents exciting opportunities to test current models of the evolution of sexual dimorphism, sex ratios, and breeding behaviour. The main theoretical objectives of my PhD project are to: 1) test predictions of natural and sexual selection mechanisms that may lead to size differences between the sexes, 2) test mechanisms that could lead to skewed offspring sex ratios, and 3) to establish clearly aspects of frigatebird ecology such as their breeding periodicity, where and on what they feed, and where they go to moult after breeding. These objectives will be achieved through behavioral observations, capture and tagging birds with yellow wing tags, collecting blood and feather samples for stable isotope analysis of diet and genetic sexing, manipulations of parental energy, and accurate census techniques. Unraveling the proximate correlates of the patterns exhibited by Magnificent Frigatebirds should generate explanatory causal hypotheses of significance to the interpretation of mating systems in birds in general, further advancing our understanding of their evolutionary ecology. An equally important goal of this project is to collaborate with local interest groups, to promote awareness and protection of the birds and the lagoon, and to advance conservation efforts of frigatebirds and other seabirds.

Photo: A.W. Diamond

 

Photos of Wing Tags


Male with wing tags in flight. Photo: Antoine Hauselmann


Male Magnificent Frigatebird sporting a satellite transmitter attached with a backpack-style harness. Photo: Geoff Holroyd


Female Magnificent Frigatebird with wing tag. Photo: Geoff Holroyd.


Locations of wing tag resightings (yellow stars) of birds captured on Barbuda (red star)


Publications

Trefry, S.A., Freedman, B., Hudson, J.M.G., and Henry, G.H.R. 2010. Breeding bird surveys at Alexandra Fiord, Ellesmere Island, Nunavut (1980-2008). Arctic 63:308-314.

Trefry, S.A. and Hik, D.S. 2010. Variation in pika (Ochotona collaris, O. princeps)vocalizations within and between populations. Ecography 33:784-795. doi: 10.1111/j.1600-0587.2009.05589.x

Trefry, S.A. and Hik, D.S. 2009. Eavesdropping on the neighbourhood: collared pika (Ochotona collaris) responses to playback calls of conspecifics and heterospecifics. Ethology 115:928-938.

Trefry, S., and Hudson, J. 2008. Breeding conditions report for Alexandra Fiord, Ellesmere Island, Canada, 2008. ARCTIC BIRDS: an international breeding conditions survey. (Online database). Eds. M.Soloviev, P.Tomkovich. http://www.arcticbirds.net/info08/ca43ca4608.html. Updated 24 Oct. 2008. Accessed 26 Oct. 2008.

Trefry, S.A., D.L. Dickson, and A.K. Hoover. 2007. A common eider X king eider hybrid captured on the Kent Peninsula, Nunavut.  Arctic 60(3):251-254.


Posters

Trefry, S. and A.W. Diamond. September 10 & 11, 2010. Reversed sexual size dimorphism in Magnificent Frigatebirds. World Seabird Conference (Victoria).

Trefry, S.A. and Diamond, A.W. May 13, 2009; July 15, 2009; August 21, 2009. Sexual size dimorphism and sex ratios in Magnificent Frigatebirds. CSEE (Halifax), SCSCB (Antigua), SCO (Edmonton).

Trefry, S.A., Freedman, B., G. Henry, and J. Hudson. May 13, 2009. Breeding birds of a polar oasis in a warming climate. CSEE, Halifax, Nova Scotia.

Trefry, S.A. and D.S. Hik. October 21, 2007. Collared pika vocalizations: influences of sympatric animals and geographic variation. ACUNS 8th International Student Conference, Saskatoon, Saskatchewan.


Note: This project is not supported by ACWERN funds, since the fieldwork falls outside of Atlantic Canada.