Abstract
A stir and murmurs ... as the first rays of the sunrise gently kiss the tops of towering eucalyptus ... an explosive cacophony of green squawking birds with wings aflutter as they exit the roost for their daily foraging foray. Eucalyptus - Australia? No. Green squawking birds - Mexico, Central and South America' No. This is a scene witnessed eve1y morning in Temple City and Arcadia, right in the confines of the lush forests of street and backyard trees, suburban Los Angeles, California, USA.
Many urbanized and suburbanized areas around the world that are already home to many introduced species, such as House Sparrow Passer domesticus, European Starling Sturnus uulgaris, Spotted Dove Streptopelia chinensis, and Rock Dove Columba Livia, have become faced with a new invader - parrots. In the San Gabriel Valley, which is where Pasadena is located, parrots have flourished, establishing self-sustaining populations, with reproduction occurring in the wild, well outside of captivity.
The exact location of the parrot roost, where they sleep for the night, changes with the change in season. In the winter, parrots converge nightly on one roost location, easily numbering over 1200 individuals and settle on broadleaf evergreen trees, such as eucalyptus, oak, and fig, since there are not many choices for suitable roost trees. An especially interesting winter roost site is in a stand of Indian Laurel Fig Ficus microcarpa trees in the brightly-lit parking lot of a busy super-
market. When spring comes, the roosting flocks decrease in size, but spread out in area, ranging from Arcadia to western Pasadena. The roost flock breaks up into smaller and smaller flocks because the parrots are tending to choose to roost in newly leafed-out deciduous trees, such as Western Sycamore Platanus racemosa, Sweet Gum Liquidambar strycaflua, and Silver Maple Acer saccharinum. Parrots are also in smaller roost flocks in the spring and summer because they prefer roosts closer to their nesting locations. Parrot chicks reach their peak in September, making up over 10% of the flock (roughly equivalent to over 50 chicks in a flock of 500).
We categorize the free-flying parrots into five major groups: "amazon"-type, "conure-type, Rose-ringed Parakeettype, Brotogeris-type, and "other" (macaws, cockatoos, cockatiels, budgies, etc.). The majority of Amazona are Red-crowned Amazona inridigenalis and Lilac-crowned Aifinscbi parrots, but small numbers of Blue-fronted Parrot A. aestiva, Red-lored Parrot A. autumnalis, White-fronted Parrot A. albifrons, and Yellow-headed Parrot A oratrix have been documented as breeding, too.
Mitred Parakeet Aratinga mitrata, Red-masked Parakeet Aratinga erytbogertys, White-eyed Parakeet Aratinga leucopbtbalmus, Bluecrowned Parakeet Aratinga acuticaudata, and Black-hooded Parakeet Nandayus nenday are the "conure"sized parrots. They are present in the eastern and far southwestern portions of the valley. Yellow-chevroned Parakeets Brotogeris cbiriri and Roseringed Parakeets Psittacula lerameri are also found throughout the area. Yellow-chevroned Parakeets tend to he found in botanic gardens (e.g. Huntington Library and Los Angeles County Arboretum) because of their dependency on Silk Floss Cborisia speciosa trees as a food source. A flock of less than 20 Rose-ringed Parakeets is often present in the Amazona roost.
Parrots are sustained and thriving due to the prevalence of exotic plantings, especially fruit trees and street trees. When considering parrots as successful urban colonizers, it. is important to consider cities as habitat. There are many common characteristics among city habitats. Most cities contain natur-. al waterways like creeks, rivers, etc. Often these waterways are humanaltered into concrete washes, flood
control channels, debris basins, and reservoirs. Natural habitat is often entirely replaced with exotic vegetation, which is generally clumped into groves and stands due to hath homeowner and city planning preference for particular species. The wellgroomed city has little under-story and trees are pruned frequently. Backyard fruit trees and remnant orchards arc often abundant and provide a source of food for many types of animals. Cities have structures such as buildings, power lines, power poles, radio towers, and highways, which act as harriers to animal movements and sources of mortality, hut are also utilized as nest sites, roosts, cover from predators, and perches for predators.