Parrot Care: Parrot Reproduction and Mortality

Reproductive studies normally entail locating adequate samples sizes of potential nesting pairs and determining both the fraction that fail to breed and the success rates of the ones that do. In some species, such as the kakapo (Strigops habroptilus), Puerto Rican parrot (Amazona vittata), yellow-headed parrot (A. oratrix), and many macaws, major problems lie in failures to lay eggs; while in others, problems may lie mainly in poor success of egglaying pairs (Snyder et al. 1987, Munn 1992, Elliott 1996, Enkerlin in litt. 1997). Thus, it is important to study both factors.

In some species which show low breeding effort (frequent failures to lay eggs), the problem can be traced to low availability of nest sites. This can sometimes be remedied by providing additional sites. For example, redtailed black-cockatoos (Calyptorhyncus banksii), which are believed to face low nest-site availability, have quickly occupied artificial sites (Emison et al. 1994b). In other species where such problems have been suspected, however, artificial sites have not been accepted, and it has been necessary to improve deficient natural cavities to attract nesting birds (e.g., red-fronted parakeet Cyanoramphus novaezelandiae – see Hicks and Greenwood 1989). In still other species which reject artificial sites, even massive provision of improved natural sites has not cured chronic problems with low breeding effort (e.g., the Puerto Rican parrot). Here, causes of low breeding effort have remained elusive, perhaps lying with food limitations of one sort or another, or with other factors such as unbalanced sex ratios in extremely small populations.

Poor nest success can be determined only by comprehensive nest monitoring efforts, which normally will include periodic nest inspections to determine growth and development characteristics of nestlings and to determine if the nestlings are affected by parasite or disease problems. With basic precautions, such inspections can usually be done without significant negative effects on nesting success, and the benefits obtained from the information gathered normally far exceed any risks entailed.

Species affected by food limitations may show slow growth effects or brood-reduction effects. For instance in south-western Australia the growth rates of a food-stressed and declining population of Carnaby’s cockatoo (Calyptorhynchus latirostris) were lower than those in a stable one (Saunders 1986). Species affected primarily by nest predation problems will generally exhibit total losses of broods, and here it may be necessary to initiate intensive nest observations to determine the culprits and possible means of thwarting them. Habitat deterioration problems are perhaps most likely to manifest themselves in effects on food supplies or nest availability, and thus be reflected in low reproductive effort, reduced clutch size, poor nestling growth rates, and/or low fledging success.

In many regions the primary nest predator will turn out to be man, as revealed by damage to nest sites or other clues (e.g., spike marks on trees). But in some species, where nest contents are easily accessible from entrances, few signs of human depredations may be evident even when such depredations are a major problem. Other principal threats to nest success include non-human nest predators and competitors, such as various snakes and lizards, pearly-eyed thrashers (Margarops fuscatus), brushtailed possums (Trichosaurus vulpecula), and feral rats and cats. On occasion nest parasites such as various bot flies and soldier flies can be a major stress. In some instances the impacts of such natural and unnatural enemies can prove adequate in themselves to account for population declines. Island parrots (e.g., the kakapo Strigops habroptilus) have proved to be especially susceptible to nest losses caused by introduced predators.

Mortality studies are often more difficult, expensive, and time-consuming to conduct than reproductive studies, but especially with very long-lived species, good quantitative estimates of mortality rates may be crucial for diagnosing whether the species is stressed by excessive mortality. A number of techniques have been used successfully. For example, many species exhibit strong fidelity in nesting territories, and if individuals can be recognised by idiosyncratic characteristics or by artificial marks, such as bands, adult turnover rates in known territories can be determined over a period of years (see Snyder et al. 1987). Although such rates are not strictly equivalent to adult mortality rates (as there may be some movement of birds out of known territories to unknown locations) they can provide a good upper boundary on adult mortality rates and in many cases are very close to adult mortality rates.

Mortality rates of fledgling birds can sometimes be determined by close study of family groups, as fledglings of some species remain closely associated with their parents for long periods – sometimes to the beginning of the next breeding season. By determining the numbers of young fledging in a reasonable sample of territories and by later determining the numbers of surviving young, mortality rates of fledglings can be calculated in a straightforward manner.

However, in some species young do not stay with their parents for long after fledging, or families disperse from breeding territories soon after fledging and do not return as families later. For such species the above method cannot be used, and determining fledgling mortality rates may necessitate marking samples of young (e.g., with radiotags) to follow their survival directly. Similarly, survival rates of adults in species that do not exhibit territory fidelity may not be determinable without marking techniques. Radio-telemetry attachments have now been tested on many of the larger parrots with success, and units are now available that have lifetimes of several years. Radio-telemetry, however, is a relatively expensive technique and entails some risks associated with capture and handling of birds. Where it is possible to gain mortality information without it, this is sometimes a preferable option. However, radio-telemetry is often the only way to determine exact causes of mortality, and can also often provide other very useful information (e.g., on range use, foraging behaviour, and migration behaviour) that often cannot be obtained by other means.

Another technique that has been used successfully to obtain mortality rate information is patagial tags (see Rowley and Saunders 1980, Saunders 1988, and Smith and Rowley 1995), although risks and benefits of these tags vary for different species. Banding (ringing) is useful as a marking technique for only certain species, as in many parrots feathers cover the tarsus sufficiently to obscure vision of bands, except when birds are in the hand. Banding with standard flat bird bands also poses risks of damage to legs in many species because of shape of the tarsus, and should always be tested carefully with captives before widespread implementation.

Adults and fledglings do not represent all age classes in a population, but they can normally be expected to represent the groups with the lowest and highest mortality rates, respectively. Mortality rates of intermediate-aged birds can sometimes be inferred from accurate data on population figures, reproductive rates, and mortality rates of adults and fledglings (see Snyder et al. 1987). They can also be determined directly by means such as radiotelemetry.

Expected mortality rates for the species under study can be estimated by comparisons with other species with similar demographic characteristics, such as age of first breeding, clutch size, etc. If the rates with the species in question appear excessively high, it is crucial to identify specific causes of mortality, and here radio telemetry may be essential. With some species hunting or trapping for the bird trade may cause excessive mortality. With others, there may be unusual situations regarding disease, toxic materials, or exotic non-human predators.

Reproduced with permission of the International Union for Conservation of Nature and Natural Resources and the World Parrot Trust.