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Galápagos Mockingbirds

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Ian Suzuki

on 21 March 2012

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Transcript of Galápagos Mockingbirds

"The distribution of the tenants of this archipelago would not be nearly so wonderful, if, for instance, one island had a mocking-thrush, and a second island some other quite distinct genus... But it is the circumstance, that several of the islands possess their own species of tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analagous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder."
- Charles Darwin
by Ian Suzuki
What is a Mockingbird?
Passeriformes - Passerines
Mimidae - Mimids
Mimus* - "conventional" mockingbirds
macdonaldi - Hood Mockingbird
melanotis - San Cristobal Mockingbird
parvulus - Galápagos Mockingbird
trifasciatus - Floreana Mockingbird
Evolutionary History
After the original *single* colonization event, diversification happened as the islands formed
Dispersal appears to have followed a wind-based pattern (South -> North)
Recent studies regarding the mockingbirds have conflicted with their methodology and results...
Galápagos Mockingbird
Hood Mockingbird
San Cristobal Mockingbird
Floreana Mockingbird
Speciation in progress?
image credit: http://fishoncomputer.wordpress.com
Mockingbirds in the Galápagos are thought to have descended from the Bahama Mockingbird ... probably.
Most common mockingbird, and is native to Fernandina, Isabela, Santiago, Santa Fe, Genovesa, Pinta, Marchena, Wolf, and Darwin (and other small islands)
Why aren't there more mockingbirds?
1. Limited habitat
2. Wind-dependent dispersal
Makes it difficult for two species or subspecies to be forced into sympatry and thus go through adaptive radiation
3. Few morphological differences between subspecies
Arbogast et. al. 2006
Greets visitors and is very inquisitive!
Native to Hood (Española)
Similar to the Galapagos Mockingbird, but is particularly aggressive and fearless
Forms larger than average social groupings
Endemic to San Cristobal Island
Somewhat shyer than the other mockingbirds
Smaller groupings (usually just pairs)
Classified as endangered, and population numbers are thought to be declining
Known to drink blood
Extirpated from Floreana, found only on Champion and Gardner-by-Floreana (total .9 square km)
320-550 individuals left between the two islands, very few breeding pairs
Low genetic diversity on Champion
Classified as Critically Endangered
Not found on Pinzón, and it is possible that it was once native there
Conservation Status
Only the Galápagos Mockingbird is classified as Least Concern
Efforts to reintroduce Floreana Mockingbird populations to Floreana are underway, but challenges remain
Genetic diversity (esp. on Champion)
Invasive species
Uncertainty of which population is more like the original Floreana pop.
Low effective population size
Vulnerable mainly because of its extremely limited range (60 sq. km)
San Cristobal
Invasive species (primarily rats and parasites) have taken a heavy toll on the San Cristobal Mockingbird
Though San Cristobal is much larger, there is more of a human impact on the island than on Española
The Galápagos Mockingbird is polyphyletic!?
*Changed from Nesomimus in 2007
The largest of the mockingbirds in the Galápagos
One major climactic event could have a huge impact on this population's numbers (La niña in particular)
Has the most diverse diet, and seems to be very adaptable
Has larger territories without "nest helpers"
Lower population density
Relatively high effective population size
It is thought that egg predation by rats was responsible for extirpating the original Floreana population (1850s)
Social Structure
"Helpers at the nest"
Quote time!
4. Less time (?)
Are these separate species?
Evolutionary Confusion!
Hoeck et. al. 2010
Arbogast 2006
Štefka 2011
mtDNA largely does not follow morphological taxonomy
nucleic DNA DOES follow current taxonomy
Supports Arbogast 2006, researchers used both sets of data and the phylogenies of co-evolved parasites
All the mockingbirds prefer the arid zones
Having said all that...
Shrubland seems to be optimal, though the Floreana Mockingbird can be found deeper
All major islands are inhabited by mockingbirds except Pinzón, Floreana, and Baltra
Very, VERY omnivorous
Opuntia flowers
Small lizards
Young turtles
High degree of local and temporal adaptation
image credit: Brent Smith
image credit: Brent Smith
image credit: Brent Smith
These mockingbirds have a plastic social structure that changes based on sex ratios
Social monogamy when males > females
Polygyny when females > males
Smooth-billed Ani and feral cats prey on nestlings
Typically live in large social groups (depending on subspecies, from 2-30 members)
Non-breeding birds often help breeding birds raise chicks
Helping behavior is much more common among kin and is partially learned
Very unafraid of humans!
Each social group defends its territory vigorously throughout the year
Breeding takes place depending on local conditions
Sometimes multiple females will use the same nest
image credit: Brent Smith
Breeders can help with other nests
Males have dominance hierarchy, the alpha male defines limits of territory
If conditions are unfavorable, the birds will not breed
When a breeding male is disrupted, he often helps the pair that disrupted him (typically his parents)
Being helped as a nestling is a stronger predictor than kinship for future helping behavior
image credit: Brent Smith
Altruism is cool!
image credit: http://mountainsoftravelphotos.com
image credit http://www.birdsasart-blog.com
image credit: http://www.flickr.com/photos/wild-boar/
Parents place a lot of pressure on young to help at the nest, can disrupt breeding
Grant, P.R. and Grant, N. 1979. Breeding and Feeding of Galápagos Mockingbirds, Nesomimus parvulus. The Auk , Vol. 96, No. 4 (Oct., 1979), pp. 723-736
Curry, Robert L. 2009. Galapagos Mockingbirds. http://oikos.villanova.edu/nesomimus/About.html
Galapagos Mockingbird. ARKive: Images of Life on Earth. http://www.arkive.org/galapagos-mockingbird.
Mockingbirds of the Galapagos Islands. Boardman, Connie. http://eebweb.arizona.edu/courses/galapagos
Hoeck et. al. 2010. Differentiation with drift: a spatio-temporal genetic analysis of Galápagos mockingbird populations (Mimus spp.). Philosophical Transactions of the Royal Society. vol. 365 no. 1543:1127-1138.
Arbogast et. al. 2006. The Origin and Diversification of Galapagos Mockingbirds. vol 60 no. 2:370-382.
Štefka et. al. 2011. A hitchhikers guide to the Galápagos: co-phylogeography of Galápagos mockingbirds and their parasites. BMC Evolutionary Biology. 11:284
Rothman, R. Land Birds of the Galapagos. http://people.rit.edu/rhrsbi/GalapagosPages/mockingbird.html
Mockingbirds are cool!
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