by Fern Van Sant on 06 December
Avian reproductive behaviors observed in the wild......such as pair bonding, courtship regur...
Most, but not all, psittacine companion birds survive in the wild in flocks. Many of the behav-iors that make these birds so appealing come from flock adaptations. Whether it is due to their ex-tremely social nature, their ability to mimic or their very demonstrative behaviors, these birds are able to integrate themselves into human flocks as pets. It is not surprising that species adapted to life in a flock are relatively easy to get along with. Equipped with a powerful beak, it appears that most gre-garious birds evolved ways to settle disputes with displays and postures instead of fighting. The drive to be part of the flock and communicate expressively enhances the appeal of these beautiful birds.
Another aspect of flocking is the learned "social facilitation". (6) To function in a flock each individual must learn to function as one part of a cohesive group. Whether in flight, on the ground or perching in trees, each individual must be alert to signals of danger, available food and opportunities to bathe or relax. To facilitate flocking, there must be clear and constant communication among the group. They use vocalizations and body signals. Individuals must respect and maintain a critical distance from each other. Flashes of contrasting body color may be another way of maintaining contact in dense foliage. There is no doubt that an innate ability to conform is necessary to maintain flock structure. (6)
With rare exceptions, psittacine species are diurnal. Most species become active around dawn and usually leave the roosting site to congregate at a feeding area. Although psittacine species are distributed among five continents and have established themselves in a wide array of environmental niches, most species can be relied upon to demonstrate regular and recurring patterns of moving and feeding through specific areas. The same predictable pattern is seen at the end of the day. Most spe-cies feed again in the afternoon then return to roosting areas for the night. Most psittacines are quiet and still through the night although there are reports of movement and vocalizations by some species on bright moonlit nights. The pineal gland contains photoreceptors that sense light independently and through visual pathways, and is probably very important in maintaining the circadian rhythms ob-served in psittacines. (4) It is likely that the pineal gland plays a critical role in triggering seasonal re-production by way of the hormones melatonin and serotonin. (12)
Parrots are notorious for their loud, raucous calls. Larger psittacines are capable of impressive volume. Most parrot calls are harsh and unmelodic, often short bursts of noise repeated for effect. Al-though simple, they effectively allow for warning, greeting and for locating flock members. Due to the amazing range of tones, cognitive skills, and ability to mimic, the vocalizations of African Grey Parrots (Psittacus erithacus) has been extensively studied. There is ample evidence to support the use of these complex vocalizations to signal danger, communicate location and possibly support social order in the flock. (8) In many birds, characteristic vocalizations have been identified as innate behaviors. Given the range of vocalizations in parrot species and the observed ability of some parrots to vocalize in specific ways without the benefit of conspecifics, the basis of psittacine vocalizations could be con-sidered an example of innate behavior.
Visual displays play an important role in communication among psittacines. Visual displays help settle disputes without physical contact. Visual displays during courtship and breeding communi-cate hormonal readiness and facilitate optimal timing for breeding. (6,7)
Seasonal migration as a means of following the food supply is seen in a few parrot species. The Great Green Macaw (Ara Amigua is known to seasonally migrate from coastal lowlands in Costa Rica to higher elevation forests in Nicaragua. (13) Two species of grass parakeets migrate over the Bass Straits of Australia, across 120 miles of open water to Tasmania, to breed each year. (6) The Patagonian Conure (Cyanoliseus patagonus) migrates during harsh winters to warmer areas of Uru-guay. Species living at high altitudes in the Andes migrate vertically to lower altitudes during winter. (14) Thick-billed Parrots (Rhynchopsitta pachyrhncha-pachythncha) used to migrate from northwestern Mexico to southern Arizona where they found abundant Pinon Pine nuts. These migrations have ceased as populations have dwindled under the pressures of hunting and development. These birds currently migrate within Mexico.
Seasonal migrations are thought to be initiated by changes in light. Fluctuating seasonal pho-toperiods, subtle changes in light wavelengths or possibly temperature fluctuations seem to initiate the hormonal events that direct migration. Corticosterone and prolactin, triggered by changes in the pitui-tary gland, are thought be integral in the hormonal regulation of migration. 12)
The complex set of innate and learned behaviors that drive reproduction and the physiologic mechanisms that underlie the process are inordinately complex. When reduced to the simplest terms, common themes emerge. In both mammals and birds, specific, and usually age-related changes sig-nal reproductive competency. In female mammals, the regular recurring pattern of menstruation be-gins and signals the beginning of a finite time period of reproductive competency. The regular recur-ring pattern is only interrupted by severe circumstances like illness or starvation. In a regular timed event a female will be fertile and able to conceive. The physiologic regulation of these events is con-trolled by the hormonal centers of the brain and the ovaries. Often called the hypothalamic-pituitary-gonadal (HPG) axis, these endocrine pathways regulate reproduction. Similar mechanisms exist in the male and result in the production of testosterone, the hormone that directs the reproductive drive of males. (25)
Birds have evolved a very similar physiologic mechanism to control reproduction. As in mam-mals, the HPG axis in birds regulates reproductive events. Several key differences are seen in birds. Since the capacity for flight demands that weight be minimized, females have only one active ovary. Birds further minimize their weight by maintaining inactive and atrophied gonads during most of the year. Only when conditions are favorable for breeding will the HPG axis stimulate activation of the ovary and testes. (26,27) During breeding season these organs may weigh many times more than the inactive gland. This adaptation necessitates a mechanism for effectively signaling the body when breeding season arrives. In temperate climate zones photoperiod, or day length, is a common trigger. In tropical and subtropical locations avian species have adopted a myriad of environmental triggers to signal breeding season. Whereas the triggers may vary widely among avian and even psittacine spe-cies, the basic mechanism of the HPG axis remains the same. Defining and understanding the differ-ent triggers and their effect on different species is clearly necessary before we can attempt to under-stand and modify the behavior of companion psittacines. Equally important, considering the compan-ion bird perspective, is an understanding of how the process needs to be self-limiting and turn itself off. An appreciation of the economy, beauty and necessity of this adaptation has been largely missed by those familiar with companion psittacines. (4,6,7,11,12)
Two key issues that we may have missed are: 1) psittacines are normally "turned off" or repro-ductively inactive in nature during most of the year. This is as Mother Nature intended, and: 2) the conditions of pet bird care may result in triggering reproductive behaviors. These surroundings of abundance are typical of pet care and reflect our affluent lifestyle, but may have a serious downside to the health of our companion psittacines.
In most animal species, reproductive behaviors are a complicated blend of innate and learned actions. Psittacine species include a phenomenal array of tropical and subtropical birds that have adapted to a wide range of habitats. Observations of wild and captive parrots reveal many species-specific behaviors that have at their roots innate or genetically determined responses. (5,14,15) A better understanding of these behaviors and the conditions that trigger them will be necessary to prevent or reverse degenerative conditions resulting from unchecked and unnecessary hormonal drives.
As most parrot species are tropical or subtropical, where photoperiods vary minimally, a flexi-ble reproductive strategy that keys to favorable climactic events - rather than day length - is essential. In areas with varied topography and incredible species density, an amazing number of unique strate-gies characterize psittacine seasonal reproductive triggers.
As part of the process of adaptation to their unique environments, each species has developed signals to time their yearly breeding with the most favorable conditions. Although well defined by lati-tude, terrains and micro-climes of the tropical and subtropical part of the world are characterized by widely variable topographic and climatic conditions. Many areas are characterized by the high humid-ity, substantial rainfall, lush vegetation, low elevation and stable temperatures considered typical of a tropical rainforest. Other regions have volcanic mountains, dry forests and even arid, desert-like con-ditions. In some areas, topography may change dramatically over short distances. In response to these varied environments, psittacine species have evolved many unique strategies to determine nest cavity availability, food and water availability and seasonal migration patterns to ensure successful reproduction. These seasonal triggers vary significantly among psittacine species and are dependent on environmental conditions specific to the birds' range and ecological niche. (6,11,13)
Some birds may rely on seasonal rainfall to trigger seasonal fruiting and subsequent food abundance. Other species, especially those in very arid regions, may breed in response to available water brought by fickle and unpredictable rains. It seems that some species are triggered by a sea-sonal climactic event that provides a glut or abundance of food. Other species that have adapted to harsh environmental conditions breed when there is relief from usually limiting conditions. These dif-ferences may prove to be very useful when attempting to understand and modify the behaviors of specific companion psittacines. (6,7,11)
In the same manner that these birds developed successful ways of flocking and feeding, they have also developed reproductive strategies that conserve energy and time. Again, specific attributes can be linked to environmental conditions. Most psittacines are monomorphic and many form stable pair bonds. The pair bond offers a distinct advantage in undertaking the all-consuming commitment to hatching and rearing altricial young. Birds that use this reproductive strategy are typically ready to breed without the need for elaborate courtship rituals. When the climate and food supply support re-production, the birds are ready. Although stable pair bonds are common among all avian species, these adaptations are well suited to the tropical and subtropical distribution of psittacines. (7,11)
Many of the larger psittacine species developed behaviors like stable pair bonds that made it possible to react quickly to favorable conditions. In many cases these stable pair bonds also facilitated the difficult task of raising altricial young. For example, in most species of macaws, successful ovi-position, incubation and feeding require the resources of both parents. It has been observed that the male will even super-feed the female prior to egg laying. This caloric boost may stimulate ovulation and may help ensure caloric support of the hen during this physiologically demanding time. Although two to three eggs are laid, the first egg will have a clear advantage as by hatching first it will have a clear head start over nest mates and will more likely compete successfully for food. This mechanism allows reproductive flexibility and will match available food resources to clutch size. In years where food is scarce, resources will be directed to the first chick ensuring at least the survival of at least one chick. (5,14,15)
A number of strategies have been observed in species of psittacines that inhabit areas with scarce water resources. The most common is that of dimorphic coloration. Several species of tough, adaptable birds have managed to thrive in the arid interior of Australia. Most of these species are small birds that rely on flock strategies for survival since they commonly ground-feed, have strong startle reflexes and fly well.
Some species, especially those where water availability is critical, key their breeding season to fickle rainfall. In areas where water is the limiting factor, many species developed ways to find mates and breed quickly in response to rainfall. The biologic basis for dimorphic species has probably evolved in response to a wide variety of environmental pressures. Dimorphic colors are more likely to reflect a strategy that allows for rapid recognition of breeding partners in response to favorable envi-ronmental conditions that are likely to occur irregularly and suddenly. Dimorphic coloration may also offer nesting females the protection of camouflage. Dimorphic coloration is common in Australian spe-cies. Rosellas and several other species of Broadtail Grass Parakeets display dimorphic colors. Budgerigars (Melopsittacus undulates) and cockatiels Nymphicus hollandicus) employ this same strategy. Budgerigars also reflect their hormonal status and gender with hormonally responsive changes to the cere color. A blue cere in a mature male and a rough brown cere in a female indicate active breeding condition. Eye color commonly reflects the gender of cockatoos, with the intensity of the female's red color reflecting hormonal status. (5,14)
One great exception to the trend of dimorphic colors is the Eclectus Parrot (Eclectus roratus). The female red and the male vivid green were long thought to be separate species. The limiting factor in their range is neither rain nor food. Some Eclectus have been observed to breed in cooperative groups. Some groups are known to use traditional nesting trees. These birds are also known to breed year-round. (5,16)
In addition to color differences, male cockatiels and budgies utilize specific vocalizations that elicit breeding behaviors in females. In budgerigars specific areas of the brain have been identified that are similar to the well-studied song nuclei of passerines. The warble of the male budgerigar seems to be a learned testosterone-driven behavior. (17)
Budgerigar males woo hens with a warble that continues in four-minute bursts and may con-tinue for hours. Cockatiel males court females with shrill whistles and females ready to breed answer with incessant chatter. Orange Chinned Parakeet (Brotogeris jugularis) pairs exhibit a back and forth chatter so well coordinated that it sounds like it is coming from a single bird. The sequences of calls seem to help coordinate and synchronize breeding behavior. Some cockatoos begin their courtship with loud vocalizations that grow progressively quieter as the pair mates, the female lays eggs and the pair begins the work of incubation. (6,14)
Courtship displays among psittacines are relatively simple when compared to other, more elaborate bird displays such as those seen in cranes, herons or peacocks, but are often impressive and complicated in their own right. Since many parrots maintain stable pair bonds, courting behaviors usually involve a variety of simple moves like hopping, bowing, strutting or tail wagging. Excited or aroused psittacines may exhibit pinning of the pupil and blushing. Macaws and Palm Cockatoos (Pro-bosciger aterrimus) can display a rush of color in their facial skin. Many Australian and Indonesian birds have impressive crests that can be used in very demonstrative ways. Head bowing, an invitation for mutual preening, is often intensified during breeding and courtship and seems able to convey sex-ual signals. Physical contact intensifies dramatically during breeding season. Although social preen-ing in not uncommon among parrots, there are many nomadic species that reserve physical contact for breeding and fighting. For species that usually maintain a discrete critical distance between indi-viduals, the physical contact of courtship is a powerful mechanism to synchronize males and females for successful breeding. (6,7,14)
Some species of parrots, particularly macaws, will use courtship feeding. It is likely that this extra feeding stimulates the hormonal cascades that culminate in egg laying by both stimulating hor-monal changes and providing the caloric abundance that contributes to egg production. (6,15)
There exists an incredible degree of variability among the 332 species of parrots as to their claim, possession and willingness to defend a nest site. In the neotropics, nest cavities appear to be a limiting factor to breeding. As cavities are not plentiful, birds will demonstrate fierce territorial defenses to protect their claim. Since the cavity plays such a key role in successful breeding of Neotropical species, it is not surprising that pairs of birds will incorporate a great deal of care and effort to prepare it. Research conducted at the University of California at Davis has demonstrated that cavity prepara-tion is a key component in the hormonal cascade necessary for successful copulation and oviposition. (18) Large cockatoos, specifically Black Palms, have been observed drumming with sticks in displays that appear to claim territory and woo mates. (5,6)
Clear differences are observed in the physical posture assumed during breeding in Neotropical and Old World birds. To achieve the cloacal contact of copulation, Neotropical males will mount the female with one foot holding on to a perch. In contrast, the males of Old World species will mount the back of the hen with both feet. Copulation usually lasts about a minute. Lovebirds have been ob-served copulating for up to six minutes. To achieve internal fertilization, breeding must be timed to eminent ovulation. Oviposition, or laying, usually follows ovulation by roughly 12-24 hours. Generally a clutch of determinate size will be laid before incubation begins. Clutch size appears to be an innate genetically driven characteristic. (5,6,19)
Work done in Peru by Charles Munn identified nest cavities as the primary limiting condition for Scarlet (Ara macao) and Green-winged Macaws (Ara chloroptera) in tropical Peru. When artificial cavities were provided high in the canopy, pairs of macaws quickly set up housekeeping. Biologists have noted that several species of macaws and Amazons have established stable shared ownership of nest sites. One species will use the cavity for several months and relinquish ownership to another species after fledging chicks. (15)
A few species of parrots are colony breeders that construct elaborate nests. Eclectus parrots have been observed breeding in colonies. It appears that several males may work together to support a nesting female. (14,16)
Monk Parakeets (Myiopsitta monachus) build huge nests that serve as roosting sites as well as breed-ing cavities. These nests are constantly built and remodeled over many years. Monk Parakeets dem-onstrate impressive building skills that enable them to build large freestanding nests in treetops. (6,14) Classic Monk Parakeet nests have been found in New York City and Chicago where feral birds have established successful breeding colonies.
Several species of Lovebirds transport leaf litter, bark and twigs for elaborate nest construc-tion. In what appears to be an innate behavior, Peach Faced Lovebirds (Agapornis roseicollis) tuck long pieces of nest material across their back secured by the feathers of the lower back. Lovebirds with white eye rings carry nest material in their mouths. Other species carry small pieces tucked under their body feathers. (6) William C. Dilger investigated these behaviors more than 30 years ago at the Laboratory of Ornithology in Ithica, New York. Dilger found that both the method of carrying material and nest design were behaviors with a clear genetic basis. By hybridizing species he demonstrated a clear pattern of inherited nest construction behaviors.
Some species of birds carefully hollow out, reinforce and set up nests in termite mounds. Some species have been noted to take full advantage of the insulating qualities of the mound.
Most large parrots lay small clutches of one to three eggs. Parrot eggs are relatively small and are incubated for a fairly long period of time. The very altricial young are tiny and helpless at hatch. The value of a strong, well-protected nest is untold considering the substantial investment in time and energy that large psittacines devote to their offspring. Female macaws assume the duty of incubation while the male ensures that she is fed and protected. Cockatoos share incubation duties. Many of the smaller nomadic parrots have a different strategy. These birds typically produce large clutches with relatively short incubation times. The young develop quickly, fledge and mature to independence quickly. (5,6,14)
Thermoregulation is exceedingly important to ensure successful incubation. In hot, humid, tropical areas it can be assumed that adaptive physiologic mechanisms ensure stable body tempera-tures in the brooding parent. Thermoregulation of avian species has been investigated and seems to be controlled by the anterior hypothalamus and peripheral receptors. The patagium of the wing has long been considered to be a principle site of thermoregulation in flight and at rest. Other sites likely to play a role in critical thermoregulation are legs, abdomen and possibly feet. (4,20)
It seems that in most psittacine nests, the young are relatively safe from danger. Because of this relative safety, young psittacines are not under environmental pressure to fledge early. Lovebirds emerge from their holes after 43 days. Lories and Lorikeets fledge after seven or eight weeks in the nest. African Grey Parrots take 70 days and large macaws may not emerge for three months. The young are commonly encouraged to take their first flight by calls from their parents. Fledging is usually preceded by days of increasingly strenuous flapping of the wings. Most parrots leave the nest capable of strong flight. Landings, turns and navigation must be learned. (5,6,14,15)
Although the first flight signals the beginning of an independent life, young psittacines have to be taught to feed themselves. Transition and training times vary with the size of the bird and the com-plexity of feeding practices. Whereas Budgerigars emerge and become self-sufficient quickly, larger psittacines like macaws may stay with their parents for many months and possibly years. Young Galah Cockatoos (Eolophus roseicapillus) have been observed to gather in nurseries of crèches, where several adults will watch over the young birds. Whether supported for weeks or months, fledg-ing signals an important developmental milestone of young chicks. Young birds must quickly learn to feed themselves and assimilate into the flock. Their emancipation demands that each bird quickly de-velops the skills essential for their survival. (5,6,14)
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Avian reproductive behaviors observed in the wild......such as pair bonding, courtship regurgitation, cavity seeking, nest building, territorial ag...