My avicultural career spans more than four decades. During this time, I have kept and bred a huge array of species, many of which have disappeared from aviculture or have always been very rare. These species have ranged from the Spix´s Macaw Cyanopsitta spixii to the Prioniturus parrots. During these more than 40 years of keeping parrots, one group has proved more enigmatic than the others: the cockatoos. They are exceptionally intelligent, hardy and complex. I have tried again and again to understand why some males aggress their mates yet that answer still eludes me, though each passing year brings new revelations.

Male cockatoos, including those from long established pairs that have bred very successfully for many years, can suddenly cause great pain to their keeper, who finds the hen viciously injured or dead; the mandible will display trauma and in some cases the head, wings and body will display bite marks. I have found that trauma is most common to the upper mandible but that it is also seen in the lower mandible. The trauma may be as simple as some puncture wounds to as serious as the amputation of the mandible. I have also seen males that not only killed their mates but who then proceeded to remove a leg or wing, chewing on them like they would a twig when found by their caretaker.

Decades ago it was believed that the males attacked their mate because they were unreceptive to breeding. The male wanted to mate and the hen eschewed his advances. This was believed to have triggered an escalation in the attempt to mate and eventually an attack.  The occasional hen was found dead while incubating eggs or even while rearing young. These latter incidences were considered anomalies; the focus was on an unreceptive hen.

I was never fully convinced that mate aggression was solely due to rejection on the part of the female. During the years, I have spoken to various veterinarians, who have found no link to mate aggression with the breeding season or the degree of sexual stimulus in the hen; indeed in over 49% of the cases necropsied by three veterinarians, the hen displayed follicular development. Males were killing their mates as a response to factors that were not limited (though apparently include) breeding.

Until some years ago I was convinced that mate aggression was only seen in captivity. It was an artifact of captivity, of keeping two birds together in a cage from which the aggresse could not escape. I have now discarded this belief. Dead hens displaying the injuries typical of mate aggression have been found in their nest in the wild (Peter Chapman verbal communication, 2013). I also found evidence of this in Timor Leste in Indonesia, when a climber who had scaled a tree containing a cockatoo nest to measure the cavity interior, found a partly decomposed body. The bird displayed the typical crushed mandible. Also in Indonesia I was shown a badly injured bird that was near death. It was a hen and her upper mandible had been crushed. Two other incidences are suggestive of male aggression, though some predator could well have attacked the two incubating hens involved.

When I asked Don Wells, an aviculturist par excellence and a person who has had considerable field experience and whom I respect immensely, if he had ever seen evidence of mate aggression, he responded in the affirmative. He had seen hens with healed punctured wounds across the bridge of the beak. Similar observations have been made by trappers in the Solomon Islands, New Guinea and on multiple islands in Indonesia.

Aggression is most common in the white cockatoos but it has also been reported in the black cockatoos and Galah or Rose-breasted Cockatoo. In the white species, the Moluccan, Ducorps´s, Red-vented, the corellas, Major Mitchells and sulphur-crested cockatoos (both Cacatua sulphurea and Cacatua galerita) are the species in which more incidences are reported. In my opinion the long-term survival of the Red-vented and Ducorps´s Cockatoos in aviculture is doomed as a result of mate aggression.

Based on the above, we know that mate aggression incontrovertibly occurs in the wild, that it is not necessarily linked to breeding and that it must be understood and controlled in order to safeguard captive populations of several species that are in serious decline in the wild.

Let´s start to dissect possible causes and solutions.

First I will enumerate the list of alleged causal factors: illness, either clinical or subclinical; confinement in too small an enclosure; imprinting on the caretaker; agitation by other birds of their kind or even the same genus; hormonal changes; a dietary imbalance; the offering of an inadequate nest—usually too shallow; incompatibility; and the aforementioned breeding asynchrony.

Having a compatible pair is in my opinion the first line of defense. Pairing two birds that are incompatible greatly heightens the risk of injury. Allowing natural pairing and pairing birds of the same age is important and in my opinion reduces the risk. If an elderly male pairs with a younger female, a hormonal implant can lower his libido until the hen matures. Pairing two young birds if only two individuals are available would be the next best option. By growing together, one can expect compatibility to develop, though by no means does this offer a guarantee of détente.

Aviculturists have responded to the threat of male aggression by clipping the flight feathers from one wing, this to slow the male. Wing clipping is partly successful if the flight cage is sufficiently long enough to allow a hen to fly out of reach. The minimum length would be 3.6 m but much longer flight cages would be even more successful. A male intent on injuring the hen will persistently chase her until she is tired, when he moves in for the kill; I have seen such males stop eating and enter a murderous mental state that is not easily described. The longer the cage and more difficult it is for the male to reach the hen, the greater the chances the hen will remain unscathed.

Even in a long flight cage, making it difficult for the male to approach the female will further reduce the risk of injury. Offering a nesting box with two entrances will prevent the hen from being imprisoned inside, where she can be an easy target. The double-entranced nest should have a divider down the center so that the male cannot simply enter, perch near the top and block the female´s exit. The female should be able to escape easily by exiting out through the side opposite to the male. The cage should also contain obstacles to make an attack difficult. A male with clipped wings can grasp the side of the flight or perch suspended from the aviary roof to try to catch a flying female. Solid aviary sides and a roof can make this difficult. (The enclosure can have open ends and an enclosed mid section, as cockatoos come from relatively open forests and dislike dark enclosures.) The male would then be relegated to walking to the enclosure floor, across the aviary and climbing to a perch, allowing the female to flee easily. Where the cage center cannot be made solid, baffles suspended from the enclosure roof can be used. These should be suspended on multiple successions on opposite sides of the aviary. They should allow a gap sufficiently large to permit the female to maneuver in flight from one end to the other while making it difficult for the male to pursue her. Baffles are normally used for the smaller species, whose lesser weight may allow the males to glide some distance even with clipped wings.

Placing a ball on the tip of the bill has also been tried, though the beak continues to grow and the bumper (made from dental acrylic) eventually falls off. The solution (like clipping the flight feathers) is temporary at best.

Some males can be especially treacherous and cunning. I have seen cases where a male changed his attitude overnight. From being especially aggressive, he switched to a placid bird. I was optimistic the first time I made this observation as the male was repeatedly seen perching and feeding the hen. Then slowly his plan came to light. He began to remove the flight feathers from the female, this to incapacitate her. This process took days. I watched closely. Then he became a demon and would have killed the hen had someone not been nearby to interfere. She nonetheless suffered several puncture bites—one to the beak and two to the wings. The female recovered. Subsequently I watched the same behavior in other males, suggesting that the first incidence was not isolated.

In another case, a male with an acrylic bumper attached to his bill, flew at the hen, grasped her with his feet and then frantically hit the female on the head. He could not puncture her beak but caused injuries from the repeated blows.

The above incidences have demonstrated how intelligent and cunning cockatoos can be.

Flying pairs in groups after the breeding season can also have a calming effect. I have found that same sex groups are best when dealing with imprinted males, which can and will fight with one another. How the groups are kept depends on the individual birds. I have some Cacatua sulphurea eleonora and Cacatua moluccensis that I can keep together and others in which more than one male will result in explosive battles. I decide how they are to be housed depending on the experience gather over time with the individual birds. As the breeding season approaches—in our case winter and spring, the birds are separated in the summer—the pairs are returned to their cages. I often add one male at a time to a cage containing females, including his former mate. This allows me to provide the mate of choice. In 37% of the cases, the males chose new mates and did not re pair with the hen with which they bred successfully the previous year. Studies in Australia have shown an equally high incidence of divorce in wild cockatoos.

Due to the continuation of problems of mate aggression being reported, other solutions were thus needed and one was proposed. Dr. Scott McDonald developed the most contentious method of controlling aggression: beak-bisecting surgery. It involves splitting the lower mandible on the male. This eliminates the crushing strength. The birds can eat normally, but some will require periodic catching to cut the bill, which can overgrow. Though cthe procedure is controversial and was eventually recanted by Scott, I know of only one case of a male with a bisected bill being able to injure a hen.

The above summarizes the cause and methods used by aviculturists to address mate aggression. But none focus on the reason as to why males aggress their mates? Is there a behavioral aspect that we have failed to understand? I believe so. My theory is not etched in stone and will probably be modified over time. My current state of thought is enumerated below.

During more than 40 years as an aviculturist, I have bred nearly all of the cockatoo species and subspecies. I have also spent considerable time visiting aviculturists worldwide and observing these birds in the wild. Isolated observations were noted and then placed in the back of my mind as isolated examples. Today many of these thoughts have been meshed into a theory.

Thailand once had a very active trader by the name of Daeng. He kept a flock of Indonesian cockatoos in an aviary. The birds bred very successfully. I had forgotten this until Don Wells mentioned it during a lecture I gave at AVES convention in Australia in 2013. I immediately flashed back and recalled seeing multiple males threatening each other with wings open and crest raised; they screamed and lunged. I asked Daeng if he ever recorded an injury. He shook his head in the negative.  He then had an employee open nest after nest and show me the contents: eggs and chicks. The birds were breeding successfully in a colony—a situation that many would think would result in complete failure. I asked if egg breakage was a problem. Again the response was in the negative.

William Peratino has been breeding Moluccan Cockatoos for many years. I first met Will in the 1980s. I recently asked him about his method of breeding. He keeps them in a group and when two birds pair and want to nest, they are separated into a breeding cage, though the males can see and threaten each other. Another friend who wishes to be unnamed maintains a flock of Major Michell´s Cockatoo in a lanai. The group contains 11 females and 7 males. The majority are offspring of two original pairs. The cockatoos breed in ceramic jars placed between low growing plants. The males become especially garrulous when nesting, when they will chase and mock battle or perch in a central metal beam and lunge at each other. The fighting can seem vicious, though not once has an injury been recorded. The hens are relegated to the incubation process while the males spent energy in their battles. Each year young fledge into the group. Not one chick has ever been injured, though the literature contains many reports of male cockatoos attacking their male offspring when these fledge in the traditional one pair per aviary concept.

I have also seen other cockatoos breed in colonies. Australians are at the forefront of these trials, which in one particular problematic species (Callocephalon fimbriatum) also seems to have another beneficial result: halting feather mutilation. (In one Australian collection, where dozens of completely plucked Callocephalon were brought together, the birds all feathered out.) Such pairs can breed in full peace. Barry Blanch has two pairs of Callocephalon fimbriatum that nest a short distance from one another, the nests being across the aviary. Mate aggression or other means of fighting has never been reported. Zanda and Calytorhynchus black cockatoos are also bred multiple pairs to an aviary, and white cockatoos are being bred in multi-species enclosures containing other cockatoos or Platycercus or Alisterus species. The presence of the other birds seems to distract the focus on one particular individual. The use of Australian parakeets is the replication of a concept known to African cichlid breeders as “dither” fish. These other species become agitated in the presence of aggression, distracting the aggressor, or they become the focus of attacks themselves, though this rarely occurs. In the US, experiments involving the rearing of a young macaw with a pair of cockatoos is producing interesting results. When the cockatoo male becomes aggressive, the larger, bolder macaw seems to interfere, reducing the likelihood of physical contact among the cockatoos.

Observations in the wild also suggest that males may behave like my friend´s Major Mitchells or Daeng´s cockatoos. They may spend time displaying and chasing each other, often in a central tree, while the females carry out most of the incubation. I have observed males of several species sitting on an emergent dipterocarp on more than one Indonesian island. The birds would suddenly suspend themselves, flap their wings and call, then spring upright and fly at another male.  The two would scream, lunge at one another and often fly away a short distance before returning. I have observed contact on more than one occasion, but through binoculars could not observe any injuries. On each occasion multiple males gathered to display. Interestingly at the time hens were found incubating eggs. Bonnie Zimmerman, who has actively studied cockatoos in Indonesia and has more experience with wild Cacatua moluccensis than anyone I know, has also observed displays in a central tree and chasing.

The incidences of mate aggression in the wild have occurred in areas where the forest was greatly disrupted as a result of deforestation or trapping was occurring. Such activity, I believe, could have contributed to the aggression. Clearly much more data is needed to provide clarity to this enigma.

Could the inability to display and vent aggression towards one another be the reason for the aggression in captivity, where the tendency is to keep pairs isolated visually? Could the incidences of injury be lessened if pairs were kept in a large enclosure with access to attached flight cages for breeding? Could the solution be in the way cockatoos are managed and not in trying to adapt a behavior by clipping the flight feathers or bisecting their beak?

I do not have the definitive word, though my current thinking is to allow pairs to visualize groups containing both sexes, to pair only birds that have nexused from a group, to give each bird the opportunity each year to switch mates if they so desire, and to continue to gather data.

We are in the process of acquiring a piece of land to house the cockatoos so that various ideas can be put to practice. One will include a large flight containing multiple pairs. That cage will contain a maze giving access to breeding cages. Observations made here and gathered over the next few years will, I hope, clarify further the complicated personalities of cockatoos.

In the mean time, share and publish your findings. By combining the observations of many, we will begin to better understand a group that in the case of the species from Indonesia and the Philippines faces a very uncertain future in the wild. By managing our captive birds, we can work towards establishing captive self-sustaining populations and at least maintain these birds for posterity.


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