My research focuses on the evolution of avian breeding systems, particularly cooperative breeding and brood parasitism in Neotropical cuckoos. I use a combination of methods including field work, molecular genotyping, and mathematical modeling to determine the reproductive fitness of individuals in cooperatively breeding groups. Although I am primarily a behavioral ecologist, I am broadly interested in avian natural history. My past work has focused on the reproductive biology and behavior of raptors, trogons, and herons.
I received my A.B. in 2005 from Harvard University. Working with Harvard University’s Museum of Comparative Zoology, I conducted my undergraduate research thesis on the reproductive biology of the Black-headed Trogon in tropical dry forest in Costa Rica. In 2011 I received my Ph.D. from Princeton University in Ecology and Evolutionary Biology. My graduate research was done in Panama in collaboration with the Smithsonian Tropical Research Institute, with support from an NSF Graduate Research Fellowship and the Max Planck Institute for Ornithology.
My research focuses on the evolution of cooperation in the Greater Ani, a Neotropical cuckoo whose breeding biology is extraordinary even in comparison with the other members of its family. Whereas many cuckoos are specialized parasites which lay their eggs in the nests of other species, anis nest communally. Up to eight individuals construct a single nest in which all of the females lay their eggs, and all group members participate in incubation, defense, and food delivery to the shared clutch. However, reproductive competition within the group is intense: before laying her first egg, each female ejects any eggs that have already been laid in the communal nest. Each female stops ejecting eggs once she has laid her first egg, presumably to avoid accidentally removing her own. As a result, the first female to begin laying in the communal nest invariably loses at least one egg — sometimes several — whereas the last female to enter the laying sequence loses none. A main goal of my research is to quantify the reproductive costs and benefits to females of nesting communally.
Adult Greater Ani. Photo credit: Kamiel Spoelstra
Interestingly, female anis can also act as nest parasites, “dumping” their eggs in the nests of neighboring groups and providing no subsequent parental care. Host groups do have a defense against being parasitized, however. Ani eggs actually change color over time, allowing adults to distinguish between freshly laid eggs and those that have already been incubated. If a parasitic female manages to sneak into a host nest and lay her eggs during the same time window as the host females, the host group can’t recognize the parasitic egg. But if the parasitic egg is laid asynchronously relative to the host clutch, the hosts can recognize and reject it. Therefore, a related goal of my research is to understand how cooperative and parasitic strategies can co-exist in a single population, and how these strategies evolve over time.
A communal nest of a breeding group of Greater Anis, containing 10 eggs laid by three unrelated adult females. Photo credit: Christina Riehl
Unlike most birds that breed cooperatively, Greater Anis nest in groups with genetically unrelated individuals. Because individuals in breeding groups gain no benefits from kin selection, theory predicts that the direct benefits of cooperation – as well as the incentives to compete and cheat – must be quite high. I am currently developing mathematical models to understand how cooperation in non-kin groups can persist in the face of cheating behaviors.
Riehl, C. 2013. Evolutionary routes to non-kin cooperative breeding in birds. Proceedings of the Royal Society of London, Series B 280: 20132245.
• A Proceedings B "Most Read" article of 2013• Highlighted "Editor's Choice" in Proceedings B
Riehl, C. 2012. The Harris’s Hawk Revolution [Book review] Journal of Raptor Research 47:333-334.
Riehl, C. 2012. Parental care and reproductive skew in a communally breeding cuckoo: hard- working males do not sire more young. Animal Behaviour 84: 707-714.
Riehl, C. 2011. Living with strangers: direct benefits favor non-kin cooperation in a communally breeding bird. Proceedings of the Royal Society of London, Series B 278:1728-1735
• Science Editor’s Choice (S. Vignieri 2010; Science 330:1289)
• Rated “Must Read” by Faculty of 1000 (R. Pringle 2011; http://f1000.com/13357090)
Riehl, C. 2011. Paternal investment and the “sexually selected” hypothesis for the evolution of eggshell coloration: revisiting the assumptions. The Auk 128 (1): 175-179.
Riehl, C. 2010. A simple rule reduces conspecific brood parasitism in a communally breeding
bird. Current Biology 20 (20): 1830-1833.
• Rated “Must Read” by Faculty of 1000 (E. Joly 2010; http://f1000.com/6381960)
• Reviewed in Current Biology (Lyon, B. E. and D. Shizuka. 2010. (Dispatch) Communal breeding: Clever defense against cheats. Current Biology 20: R931-R933).
Riehl, C. 2010. Egg ejection risk and hatching asynchrony predict egg mass in a communally breeding cuckoo, the Greater Ani. Behavioral Ecology 21 (4): 676- 683.
Riehl, C., and S. M. Bogdanowicz. 2009. Isolation and characterization of microsatellite markers from the greater ani Crotophaga major (Aves: Cuculidae). Molecular Ecology Resources.
Riehl, C., and L. Jara. 2009. Natural history and reproductive biology of the communally breeding Greater Ani (Crotophaga major) in Gatún Lake, Panama. The Wilson Journal of Ornithology 121(4): 679-687.
Riehl, C., and G. S. Adelson. 2008. Seasonal insectivory by Black-headed Trogons, a tropical dry forest frugivore. Journal of Field Ornithology 79(4): 371-380.
Riehl, C. 2008. Communal calling and prospecting by Black-headed Trogons (Trogon melanocephalus. The Wilson Journal of Ornithology 120(2):248–255.
Riehl, C. 2007. Evidence for cooperative breeding by White-bellied Go-Away Birds (Corythaixoides leucogaster). African Journal of Ecology 46(3):421-423.
Riehl, C. 2006. Widespread cannibalism by fledglings in a colony of Black-crowned Night- Herons. The Wilson Bulletin 118(1): 101-104.
Riehl, C. 2002. Red-shouldered Hawk preys on Pied-billed Grebe. Journal of Field Ornithology 73(4): 410-411.
Riehl, C. 2001. Black-crowned Night-Heron fishes with bait. Waterbirds 24(2): 285-286.