Parrots: The Animal Answer Guide

2. Form and Function

17 What are the largest and smallest living parrots? One of my most memorable experiences with parrots was sitting on the edge of a clearing in central Brazil watching squadrons of Hyacinth Macaws (Anodorhynchus hyacinthinus) fly past, their blue bodies framed against a backdrop of green palms. Their plumage was breathtaking, but what stuck in my mind was their enormous size. The Hyacinth Macaw is the largest parrot species. It occurs as three isolated populations in Brazil. There are approximately 500 birds in the Amazon, 1,000 birds in central Brazil, and 5,000 birds in the Pantanal tropical wetlands of Brazil. The Pantanal population extends into neighboring Paraguay and Bolivia. Hyacinth Macaws are dietary specialists, each population relying on two or three species of palm nut. These palm nuts are extremely tough and difficult to crack. Birds employ different techniques for different types of nuts, but all methods are dependent on the size and configuration of the macaw’s bill. The hardness of palm nuts and the size of the Hyacinth Macaw’s bill may have increased in tandem, each species striving to gain the upper hand in an evolutionary arms race fought on the South American savannah. The large bill and associated musculature are anchored to a large head, which in turn necessitates a large body. The head remains oversized, giving flying birds the appearance of winged hammers. The Kakapo (Strigops habroptila) is a wildlife documentary staple. Recently , a male bird named Sirocco gained worldwide notoriety when filmed attempting to mate with presenter Mark Carwardine in the BBC documentary Last Chance to See. Having the world’s heaviest parrot attach itself to the back of your head is no laughing matter, and Carwardine suffered Chapter 2 Form and Function 18 Parrots: The Animal Answer Guide a number of wounds before the chief Kakapo wrangler came to his rescue . The average weight of adult males is 2 kilograms, though individuals weighing 4 kilograms have been recorded. With an average weight of 1.5 kilograms, females are significantly lighter. The sexual difference in weight of Kakapo, one of a number of types of sexual dimorphism found in birds, suggests intense competition among males for females. The Kakapo has a “lek” mating system, characterized by males gathering and displaying at arenas where they are visited by females. A few males are responsible for most successful breeding attempts, though the process of mate selection by the females is poorly understood. Males are aggressive toward each other and will fight to the death. Large size may ensure physical dominance, which assists in gaining access to the best locations within the display arena. The calls of large males may be more desirable, and heavier males may have the stamina to call for longer periods. If large males produce more offspring, male size will increase over time. The large size of female Kakapo may simply be a consequence of their genetic relatedness to large males. Competition among females for access to critical food resources may also be a factor. In managed populations, successful reproduction in females is related to the presence of mature Rimu The Hyacinth Macaw (Anodorhynchus hyacinthinus) is the world’s largest parrot. Matt Cameron 19 Form and Function (Dacrydium cupressinum) trees within their home range (the area used on a regular basis to meet daily needs). While Kakapo have overlapping home ranges, females appear to have exclusive access to core areas within their home range. Kakapo were once widespread throughout New Zealand, occupying a variety of habitats of varying quality. The ability of females to survive, but rarely breed, in suboptimal habitat would have ensured ongoing competition for high quality sites. Larger females may have been more successful in securing home ranges containing food resources necessary for reproduction. Kakapo are critically endangered and humans need to intensively manage reproductive events, making determining the part competition played in the evolution of large body size difficult. The Buff-faced Pygmy-parrot (Micropsitta pusio) is the smallest parrot, 12 times shorter than the average Hyacinth Macaw and 400 times lighter than the heaviest Kakapo. It is one of six species of pygmy-parrot found in New Guinea and northern Melanesia. The habits of these incomprehensibly tiny parrots are poorly known. They have been observed feeding on lichen and fungus, their large feet enabling them to descend head-first down the trunks of trees and to hang beneath branches. Stomach contents Table 2.1...