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Breeding & Genetics

Hormone Control

Note: this article was written specifically for cockatiels. It may or may not be applicable to other species

Click here for sciencey geek talk about breeding triggers.

Cockatiels are opportunistic breeders, and the level of breeding hormones will rise and fall for both males and females according to whether current conditions seem favorable or unfavorable for breeding. This will happen even if the bird doesn’t have a mate. But we have a lot of control over our birds’ environment, and can manipulate the situation to help control their hormone levels. These techniques work on most cockatiels. This article deals with hormone reduction to reduce or eliminate unwanted breeding behavior, but people who want their birds to breed can stimulate breeding behavior by doing the opposite of what it says here.

Why control hormone levels?

A female with a high level of breeding hormones may start laying eggs. If she has been mating with a male it’s likely that the eggs will be fertile, which can be a big problem for owners who don’t want to take on the heavy responsibility of breeding. If she hasn’t been mating with a male the eggs will definitely be infertile, and egg production will place an unnecessary burden on her physical resources. An egg contains all the materials needed to build an eggshell and a complete baby bird, and every molecule of this comes from the hen’s body. This nutrient drain occurs on a very fast schedule, too. Unlike a human mother who has 9 months to take in all the materials needed to make her baby, the average cockatiel hen will lay an egg every other day until she has a clutch of 4 to 6 eggs. It’s obviously undesirable to put a hen through all this strain unless she has a sexually competent mate and you have an active desire to breed your birds. If the hen isn’t healthy and well-nourished enough to lay normal eggs, she is at risk of dying from egg binding, egg yolk peritonitis, and other problems related to the egg-laying process.

Males obviously don’t have to face the risks of egg laying. But high hormone levels can cause behavior problems, and your male will have a sweeter temperament and be easier to live with if his hormones aren’t raging.

The time to start applying hormone reduction techniques is when you notice that your bird is getting hormonal.

What are the signs of hormonal behavior?

Aggression and territoriality, especially from males (usually related to the cage and/or an object that the bird perceives as a mate). Seeking out a location for a nest – semi-dark partly-enclosed areas are preferred since wild cockatiels nest in tree holes, but a corner in the bottom of the cage is also a popular location. Shredding paper or wood is nesting behavior, similar to a wild bird chewing up the interior and entryway of its nest hole to improve the site. Many males will sing and dance throughout the year and this is normal, but a big increase in this courtship behavior is a sign of rising hormones. Females may solicit sex by leaning forward to flatten out their back, and they might vocalize too with sort of a crying sound. Both sexes may engage in masturbation (if single) or copulation (if mated).

If you have a mated pair or a single female, it’s best to take control of the situation promptly when you see signs that the hormone levels are rising. It takes time for the hormone levels to rise high enough for egg laying to begin, and there is still time to intervene even if you’ve seen sexual activity once or twice. But if you delay too long, the hormone level might rise to the “point of no return” where it will be impossible to prevent egg laying.

How to reduce hormone levels

We reduce hormone levels by knowing the conditions that make hormone levels rise and doing the opposite. Some birds will respond to just one technique, others respond to a combination of techniques, and a few won’t respond at all.

1. Manipulating the photoperiod, aka the long nights treatment. This is by far the most effective technique, and in many cases will be the only one that’s needed. The longer days of spring and summer are a major breeding trigger, since they provide favorable conditions for food plants to grow and extra daylight hours for the parent birds to collect food for the babies. It can seem like spring all the time in our homes, since we have electric “sunlight” when it’s dark outside and pleasant indoor temperatures all year long. But we have the power to make it seem like night when it’s actually light outside, and trick our birds’ bodies into thinking that it’s winter and therefore not a good time to breed.

To do this, we make sure that our birds get 12 to 14 hours of uninterrupted darkness every night for at least a week. It doesn’t have to be pitch black but it does have to be dark enough to seem like night. Any light in the sleeping area shouldn’t be brighter than the light of a full moon; it’s OK to have a small night light. It's desirable for it to be quiet too, but darkness is more important than quietness and it's OK if there's some noise. If you have a quiet, windowless room where the bird can sleep, that’s perfect; or you can put a heavy cover on the cage to make it dark inside. You can test the light-resistance of the cover by draping it over your own head. It won’t do any good to throw a light cover over the birdcage in a room that isn't dark; this might actually make things worse, since the shadowy light coming through the cover will simulate conditions inside a nestbox rather than the night-time conditions that you want.

Once you’ve found a suitable location and/or cover, you are now in control of when “sunset” and “sunrise” occur. Follow a fairly regular schedule of 10-12 hours of light followed by 12-14 hours of darkness. In the beginning it will seem like it isn’t working because the hormonal behavior isn’t changing, but after about a week there will be a sudden dramatic reduction in breeding behavior. Once the change has kicked in you can discontinue the long nights if you want to, but be aware that hormone levels might start rising again if you allow longer days.

If a bird doesn’t respond to the long nights treatment it may respond to three or more days of nonstop bright light, or to reversing day and night by having bright lights when it’s dark outside and darkness when it’s light outside. I don’t know the biological reason for this result, but I would guess that the bird’s body is so confused that making babies doesn’t seem like a good idea. This veterinary website discusses the use of continuous light to disrupt the breeding cycle.

2. Manipulating the environment. Birds want to raise their babies in a safe and secure environment, and to discourage them we need to make the environment seem less safe and secure without actually scaring the birds. We do this by rearranging things so the house doesn’t seem as comfortable and familiar as it did before. Some of the options are to rearrange the interior of the cage (perches, bowls, toys, etc); change the location of the cage; put the bird in a different, unfamiliar cage; put the bird in a different room; bring a large, unfamiliar object into the room and keep it there; and/or rearrange the furniture in the room.

3. Manipulating the food supply. It’s a good time to breed when food is plentiful, so we have to make the food supply seem a little less abundant. Make sure that your birds have balanced nutrition and enough food to get through the day, but don’t provide so much that it seems like there’s enough available to feed babies too. Parent birds prefer soft foods for their babies so emphasize harder foods and minimize the amount of softer foods.

4. Eliminate nesting sites – this means NO happy huts! Don’t let your bird have regular access to anything that resembles a suitable nesting place; this applies to both males and females. There are some parrot species that sleep in a nest hole all year long, but cockatiels are not one of these species. The ONLY thing they use a nest for is making babies, and if they have a nice nesting area they will start wanting to use it. Do NOT give them a real nestbox or a happy hut (bird tent). Don’t let them have regular access to dark and/or semi-enclosed spaces like cabinets, drawers, bookshelves, cardboard boxes, baskets, or underneath a bed or couch.

Do not provide shreddable materials; shredding and chewing is nest-preparation behavior. It’s desirable to have a cage with a grate in the bottom that prevents access to the cage paper, but if your cage allows access and your bird starts doing a lot of shredding, one option is to remove the paper and wash the poop out of the empty tray when it’s time to clean the cage. This may be a nuisance, but it’s better than unwanted egg-laying and crazy hormonal-male behavior. If your cockatiel has a preferred nest corner in the cage or elsewhere, you can put an object in that location (like a toy or food bowl) to block it off.

5. Eliminate or reduce access to real or imaginary mates.
In the case of a mated pair, you can keep them in separate, side by side cages if they are content this way, with supervised out of cage time together. Don’t try to separate them completely, it will make them unhappy and they will do a lot of screaming back and forth at each other. In the case of a single bird that masturbates with an inanimate object (or your foot!), take the object away or cover it up so the bird can’t “play” with it any more.

6. Avoid sexually stimulating activities.  Be careful about how you touch the bird. Head scritches are usually OK, but do NOT pet a hen on the back because this is sexually stimulating – it feels vaguely like a male standing on her back for copulation. There are some sources that recommend not touching males on the back as well, but it isn’t as directly sexual for males so you can get away with more of it with them. The male and female rub their vents together during copulation so you shouldn’t touch either sex in this area – not that most people would want to!

Warm foods or feeding the bird from your hand may be stimulating in species where the male feeds the female as part of the courtship ritual.  Regurgitated food is served warm. Most cockatiels don't engage in courtship feeding so it's less of an issue for them.

When does it start working?

It takes at least a week for the hormone control techniques to have a noticeable effect on behavior. For the first few days it will seem like nothing is happening, but when it finally kicks in the behavior difference will be sudden and dramatic.

Unwanted eggs are being laid. Now what?

As a general rule you should not remove the eggs unless the egg is broken or leaking (you should remove it in that case because it’s a bacteria hazard). The hen’s natural instinct is to keep laying eggs until she has a full clutch, and if you remove the eggs she will lay extra eggs to replace them. If she has laid an egg in an inappropriate place, you can put it in a suitable location in the cage.

Make sure that the hen has an ample intake of calcium and vitamin D3, and try to boost the quality of her nutrition in general. This will reduce the likelihood of egg binding, soft-shelled eggs and related problems. If your hen has symptoms of egg binding it’s a medical emergency and you need to contact a vet ASAP. If she lays a soft-shelled or no-shell egg, her calcium levels are very low and she’s at high risk for medical complications and serious problems when the next egg is laid. Quick action is needed to improve her calcium levels, and it’s best to see a vet for the fastest treatment options (calcium shots), although you might be able to solve the deficiency problem with a liquid calcium supplement made for birds. There are several different brands but they all seem to use the same formula, and contain calcium, magnesium, and vitamin D3 (the last two ingredients are necessary for calcium absorption). Some pet stores stock these supplements and some don’t, so call around until you find a pet store that has it. Follow the directions carefully since an overdose is as bad as a deficiency.

If it's possible that the eggs are fertile, you have a decision to make. If you decide to let the pair go ahead with the breeding process, you need to provide them with a suitable nestbox (click here for more info) and start learning all you can about cockatiel breeding ASAP. If you decide that you do NOT want the eggs to hatch, you can boil or freeze the eggs to kill the embryo and return the eggs to the parents after the eggs are back at room temperature, or replace the real eggs with fake eggs ( is a good source). Then follow the recommendations for infertile eggs, substituting the word “pair” for “hen” in the following paragraphs.

If there is no chance that the eggs are fertile, you want to put a stop to the breeding process as fast as possible. Immediately start applying as many of the hormone reduction techniques as you can, but keep in mind that they might not be very effective because the hen’s hormone levels are already very high. Do NOT give her a real nestbox or any kind of enclosed box, since that will help keep her hormone levels high. But do provide an open box or basket that will keep the eggs together in a reasonably safe manner, without seeming as safe and secure as an enclosed box. Let her keep the eggs for at least a week. Many birds don’t start incubating until several eggs have been laid, so she might ignore the eggs at first and start sitting on them later. If she hasn’t started incubating after a full week, you can be pretty confident that she isn’t interested and remove the eggs. If she does start incubating, let her keep the eggs until she loses interest in them, which usually takes about three weeks. Hope that the hormone reduction techniques will have an effect before the eggs reach their theoretical hatch date, because if you can’t reduce her hormone levels she might lay a new clutch to replace the one that didn’t hatch out.

Sometimes it is effective to remove the eggs as soon as they are laid and apply the hormone reduction techniques in drastic fashion. If you have a hen that has just had a major change in her life (losing her mate or going to a new home for example) this is likely to work, although she might lay another egg or two before she stops. But in general you’re taking a risk if you take the eggs away, and your hen could end up laying many more eggs than she would have laid otherwise.

Stopping a breeding pair from starting another clutch. Many breeding pairs will want to start working on a new clutch when their current babies are one or two weeks away from fledging. It’s difficult to prevent them from starting a second clutch, and if you are letting them raise the babies to weaning you don’t want to interfere with their hormone levels too much because of the risk that they might abandon the babies. A light application of the long nights treatment might help, starting when the oldest chick is about two weeks old. Make it seem like the nights are starting to get longer - for example, if the real night is 10 hours long, bump it up to 11 hours. It’s fairly easy to stop them from starting a third clutch; a light application of the hormone-reduction techniques and removing the nest as soon as the last baby fledges will usually do the trick.

Chronic egg laying is when a hen lays an excessive number of eggs and is pretty much unstoppable. This will eventually put her life at risk, but there are medical interventions that can help. Your vet can give her Lupron shots to reduce her hormone levels, and this is safe and effective in most cases. A hormone implant called Suprelorin or Deslorelin has become available and is being used in birds. It's said to be less expensive than Lupron but there isn't a lot of information online about its safety and effectiveness in birds.  This forum discussion has the best information I've seen about using it with parrots. In extreme cases, a hysterectomy will put a final stop to the egg laying. But this is a high-risk operation in birds, so it is only done as a last resort to save the hen’s life.

There have been cases where chronic egg laying stopped after the hen was allowed to hatch out and raise one or more babies (from her own eggs or “borrowed” eggs). But don’t count on this to work in all or even most cases. Most cockatiels don't lose interest in breeding after they've had one clutch, and instead they want to have more.


Breeding Triggers

Birds have evolved to be physically capable of breeding only at times when conditions are favorable to success. Their hormone levels rise and fall in response to a variety of environmental factors, and they come into breeding condition when the combined effect of these factors brings their hormones to the right level. Factors that make breeding hormones rise are called breeding triggers.

The primary sources for this discussion are Ubuka et al, Dawson, and Dawson et al.

Breeding triggers are divided into two main classes: proximate factors (which initiate the first phase in the process of coming into breeding condition), and ultimate factors (which complete the process of raising the hormone levels, bringing the birds to the point of actually reproducing).  Both phases are necessary for breeding to take place; if only one set of factors is present, the overall message sent to the bird is that it's not a good time to breed. The importance of the various factors varies by species, but birds that share similar breeding habitats tend to be influenced by similar factors.

For birds that breed seasonally, the photoperiod (day length) is the most important proximate factor. The photoperiod determines the "annual window" in which reproduction takes place (Verhulst & Nilsson). The fact that the day length is increasing or decreasing seems to be more important than whether there are more or less than 12 hours of daylight. It often doesn't take very much of an increase in day length to start things off at the beginning of cycle, and it may not take much of a decrease in day length to make the hormone levels start winding down. For example it's reported that the hormone levels of Japanese quail will rise when the day gets longer than 11½ hours. But after about 3 months of elevated hormones, the hormone levels will drop when the day length gets shorter than 14 hours. They'll get hormonal again if artificial light is used to increase the day length.

When the days start getting longer, the gonads (ovaries and testes) start developing so the birds will be ready to breed if other conditions are favorable. Increasing day length is usually a harbinger of warmer weather and a more abundant food supply. More daylight hours also mean that the parents will have more time to gather food for the chicks before darkness forces them to stop for the night. Warmer temperatures also mean less risk of eggs and chicks getting chilled.

Other factors that play a role in the early development of the gonads can include rainfall, temperature, the availability of a mate, and social interaction with flockmates.  These factors can speed up or slow down the development initiated by the change in photoperiod. Restricting food has little or no effect on the early stages of the hormone changes, but an adequate food supply is important to the later stages of ovarian maturation.

The day length doesn't change much in the tropics, so other factors may be more important than the photoperiod for tropical birds. In these species, the reproductive system may stay in a preliminary ready state for much of the year. The bird's circadian rhythm may be the main proximate factor, allowing it to come into breeding condition after a certain number of months has passed (often the time period required to complete one breeding cycle followed by a molt). However, many tropical birds do breed seasonally, and the slight changes in the photoperiod are an important breeding trigger (Hau, Hau et al). The birds can respond to an increase in photoperiod as small as 17 minutes.

What happens if you've put your birds on long nights to control their hormones but turn the light on occasionally during the night? You've probably sent them the message that the daylength is changing in favor of breeding. An experiment on quail using 18 hours of darkness and 6 hours of light found that a 15-minute pulse of light would cause development of the gonads if the light pulses occurred within 12 to 16 hours of "dawn".

Rainfall may be an important proximate factor for opportunistic breeders in arid habitats, since it stimulates the growth of plants, providing a promise of a better food supply in the near future.  This includes at least some Outback birds.  Zebra finches breed opportunistically in areas where rainfall is unpredictable.  Their hormone levels do react to changes in the photoperiod, creating some degree of reproductive readiness so they can respond quickly when rainfall occurs during the appropriate season (Perfito et al-1, Perfito et al-2). Cockatiels occupy the same habitat as zebra finches, and are considered to be opportunistic breeders too.  I can't find any scientific literature on the breeding triggers for cockatiels, but my own little flock responds more strongly to changes in the day length than to rainfall.  So it appears that the pattern observed in zebra finches applies to them too. 

In many locations, breeding ends before the return of short photoperiods. After a certain period of time, the gonads and hormone levels will start to regress, even though the days may still be be long and might even be still getting longer. In many locations, the increasing temperatures that come with longer days become a problem at some point, shriveling the food supply and causing heat stress to babies in the nest and their hard-working parents. In species that molt after breeding, it is not clear whether it is the change in photoperiod or the regression of the gonads that directly triggers molt.

The availability of an adequate food supply is believed to be the most important ultimate (secondary) factor in making breeding hormones rise. Other ultimate factors include nesting conditions, the amount of pressure from predators, and weather.   

The abundance of food can influence clutch size. The laying date is important too; in the wild, birds that breed earlier tend to have better success than those that breed later in the season. The reasons for this can include seasonal declines in food availability, seasonal increases in predation and parasites, and declines in parent fitness as the season progresses  (Verhulst & Nilsson, Ruffino et al).

There are some in the pet bird community who believe that specific types of food trigger a rise in hormone levels, for example high fat foods like sunflower seed. This appears to be an assumption however, not a finding based on careful observation.  Good breeders usually provide higher-nutrition food during the breeding season, but it appears that many birds will breed just as readily on lower-quality food as long as they have plenty of it.

A meta-analysis by Ruffino et al did not have enough data to consider food quality, but they said,

"Growing evidence suggests that the ecological impacts of food supplementation can depend on the specific nutritional profile of provisioned foods and that the energetic content of the food (in joules or calories) does not necessarily constitute an indicator of food quality. For example, the availability of essential amino acids, and vitamins or antioxidants  may constrain egg production in birds."

However, their references dealt with the influence that food quality had on the actual breeding outcomes - factors like maternal health, clutch size, egg quality, and chick survival. They specifically expressed doubt about the usefulness of extra fat during the breeding period. They did not consider the question of whether food quality is itself a breeding trigger, but the surprising results of some of the studies indicate that it may not be.

A study that provided Florida scrub jays with a high-fat high-protein food supplement throughout the breeding period found that it made little or no difference in the breeding outcome (Reynolds et al). If having more fat and protein available doesn't improve the breeding results, then there will be no selection pressure to evolve a hormonal response to these foods.

A study on blue tits found that supplementation with high-fat foods during the winter actually impaired reproductive success in the following spring; the reasons are unclear, but one hypothesis is that too much fat unbalances the diet in a way that has a negative impact on reproduction (Plummer et al). If this is generally the case, then nature is going to select against birds who insist on having fatty foods when they breed.

Copyright 2014-2016 Carolyn Tielfan all rights reserved