Posts Tagged ‘14 species of mockingbirds’

Pleistocene Mockingbirds (Mimus polyglottos)

June 9, 2018

Mockingbirds are swingers.  Most suburban yards in southeastern North America host a pair of mated mockingbirds, but they might not remain the same pair throughout the breeding season because both males and females often switch mates.  Male mockingbirds sit on the top of trees and sing long melodious songs to attract female mockingbirds from adjacent territories, not unlike the way human pop singers attract groupies.  Female mockingbirds may leave their mates for better singers.  Males also flash their wings, and this entices female mockingbirds as well.  It doesn’t matter if a male already has a mate because they will continue to try and attract other females.  Constant mate switching ensures the genetic vigor of this species.  Despite this competition, mockingbirds from adjacent territories respond to their neighbor’s distress calls and will help drive away predators, such as crows.  Each territory of swinging and singing mockingbird mates can produce 2-4 broods per year.  Mockingbirds are an intelligent bird able to recognize individual humans, and they can imitate the calls of at least 14 other bird species as well as the vocalizations of cats, dogs, frogs, and crickets.

Photo of a mockingbird in my front yard.  Click to enlarge.

Northern Mockingbird-rangemap.gif

Northern mockingbird range.

I wonder how common mockingbirds were during the Pleistocene compared to today.  Studies show mockingbirds enjoy longer lives in suburban areas than they do in wilderness refuges.  Scientists believe mockingbirds prefer the stability of manmade habitats where they can find the same nesting sites, fruit trees, and insect species year after year.  They don’t have to travel far to find favorable habitat that might be dispersed in a wilderness.  I hypothesize mockingbirds were common in the south during most climate phases of the Pleistocene, but were not as common as they are today.  Mockingbirds probably occurred in forest edge habitat along megafauna trails maintained by the regular migration of herds.  Mockingbirds could rely on fruits originating from trees sprouting in seed-filled dung, and they fed on insects stirred up by roaming large animals.  Northern mockingbirds are uncommon in the fossil record.  They are known from just 3 specimens excavated from Reddick and 1 in Haile–both located in Florida.  Bahamian mockingbirds (M. gundlachii) left fossil evidence at the Banana Hole site in the Bahamas.  This paucity of fossil evidence doesn’t mean mockingbirds were an uncommon bird in the past.  Potential sites of fossil preservation in their favored forest edge habitat just didn’t exist to any great degree.

Genetic evidence does suggest mockingbirds have an ancient origin somewhere in South America where the most species of mockingbirds occur.  Mockingbirds belong to the Mimidae family which also includes thrashers and catbirds.  There are 14 species of mockingbirds: northern, tropical (M. gilvus), brown-backed (M. dorsalis), Bahama, long-tailed (M. longicauda), Patagonian (M. patagonicus), Chilean (M. thenca), white-banded (M. triuris), Socorro (M. graysonii), chalk-browed (M. saturninus), Floreana (M. trifusciatus), San Cristobal (M. melanotis), Hood (M. macdonaldi), and Galapagos (M. parvalus).  The northern mockingbird is a sister species to the tropical mockingbird, and they are so closely related they interbreed on the border region where their ranges overlap in southern Mexico.  The Chilean mockingbird is a sister species of the Patagonian mockingbird.  The uplift of the Andes mountains separated the founding population of these mockingbirds into 2 species.  Oddly enough, the Bahama mockingbird is a sister species to the 4 kinds of mockingbirds found on the Galapagos Islands including the San Cristobal, Galapagos, Hood, and Floreana.  Each of these species occupies just 1 or 2 Galapagos Islands.  Darwin wrongly assumed they were most closely related to South American species of mockingbirds due to the relative proximity.  But genetic evidence shows the mockingbirds that traveled over the Pacific Ocean to the Galapagos Islands came from even further away.  It seems likely this occurred before a land bridge connected North and South America.  Otherwise, the exhausted birds would’ve landed on Central America instead.  Unlike Darwin’s famous finches, mockingbirds didn’t evolve into different species that occupied different niches on each island, but instead remained habitat generalists, though each became a different species unique to the island they landed upon.

References:

Hoeck, P; et al

“Differentiation with Drift: A Spatio-Temporal Genetic Analysis of Galapagos Mockingbird Populations (Mimus spp.)”

Philosophical Transactions of the Royal Society of Biological Science 365 (1543) 2010

Lovette, I; et al

“Philogenetic Relationships of the Mockingbrids and Thrashers (Aves: Mimidae)”

Molecular Phylogenetics 2011