Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Forestry, Wildlife, and Fisheries

First Advisor

Robert B. Hamilton


I studied the breeding activity, productivity and nesting success of the Thick-billed Parrot (Rhynchopsitta pachyrhyncha) during a 3-year period 1997--1999, and also analyzed preliminary data from 1995 and 1996. I studied the Parrots in six nesting areas located in the Sierra Madre Occidental in Mexico. Data were collected on breeding areas characteristics, nest site characteristics, reproductive activity, productivity, and nesting success. Most of the historical breeding range reported in the literature was searched for nests. Two main breeding areas reported in the literature continue to be the major breeding strongholds for the species. Cebadillas and Madera accounted for 56% and 18% of the nests respectively. I assessed reproductive success of 123 accessible nests. Overall, 81.3% of the nests were successful. Of 337 eggs followed, 268 hatched (79.5%) and 200 chicks fledged (74.6%). In the 5-year period, clutches averaged 2.73 and 1.62 young parrots fledged/nest. Except 1999, nesting success and fledging success were high with rates above 80%. Causes of total nest loss included: nest desertion, mammal predation, and parasite infestation. During the study, nests were found in 187 trees and snags of seven tree species. Nests occurred preponderantly in snags (58.8%). Nests averaged 75.2 cm diameter at breast height (dbh), and only 2 nests out of the total of 187 were in trees under 40 cm. dbh. Most nests occurred in Douglas fir (32.6%), and Mexican white pine (21.9%). Most nests occurred in areas with high densities of large trees and snags ≥60 cm (dbh). Nesting persisted in areas under commercial harvest, but trees and snags used for nesting were frequently logged and many nest sites were lost. Decline of the species seems to be related to large-scale logging of historical breeding and wintering range. Timber harvesting affects nest site availability in breeding areas and food supply in breeding and wintering areas. Life history traits of the species seem to enable the parrots to cope with cyclic and sometimes unpredictable food supply. High reproductive performance seems to occur in years with evidence of abundant food supply.