By Mike Fidler.
POSITIVE FACTORS AFFECTING BREEDING CONDITION
DAYLIGHT HOURS [PHOTOPERIOD]
NUTRITION – FOOD ENERGETICS + NUTRITIONAL VALUE
CLIMATE, TEMPERATURE, RAIN
SUITABLE NESTING SITES & NESTING MATERIAL
COMPETITION, PECKING ORDER
THE HORMONAL CASCADE
Counter intuitive to many aviculturists, breeding condition starts with a period of AUSTERITY. Nearly all wild birds, in all climates, in all latitudes and all habitats go through a period when food is hard to come by and is of poor quality. The bodies of the birds react to this in a number of ways including consuming spare fat and cutting off key hormonal flows, which has the effect of deactivating and shrinking the sex organs.
The birds start to come into BREEDING condition as a response to KEY TRIGGERS.
In lower temperate latitudes the KEY TRIGGER can be increasing day length, in the deserts and around the equator, it is rain. But in all cases these are triggers which signal the start of a period of abundant, nutritious and reliable food resources which ensures they will be able to feed and rear healthy nestlings.
It is worth noting that in species from lower temperate latitudes, KEY TRIGGERS of increasing daylight and better quality food can be of equal importance.
In the majority of bird species it is the better nutrition which starts the regeneration and growth of the sex organs, signalling the start of the breeding cycle.
Technically speaking, the above triggers stimulate the hypothalamus part of the brain to release the gonadotropin GnRH hormone, which then acts on the pituitary gland causing it to release three more gonadotropins. These are called FSH (Follicle Stimulating Hormone), LH ( Luteinising Hormone), and once egg laying proceeds, Prolactin.
These hormones all act on the gonads [sex organs].
FSH stimulates maturation of the gonads in both sexes and sperm production in males.
LH stimulates ovulation by females and the sex hormone oestrogen and in the males testosterone production.
Prolactin is activated by nest building and egg laying and induces brood patch development, brooding behaviour and behaviours for feeding and care of nestlings. This is achieved by signalling the pituitary to halt production of LH and FSH which deactivates the gonads during this period.
At the end of the breeding cycle the seasonal decrease of the photoperiod and/or the decrease of quality food triggers the production of the negative feedback hormone GnIH (Gonadotropin-Inhibitory Hormone) which causes the pituitary gland to stop the production of hormones, reversing breeding condition by shrinking the ovaries and testes, thus bringing the breeding season to a close, and signalling the onset of a natural austerity period.
The above applies to practically all birds but just a few have adapted to different triggers, and a few like the Feral Pigeon, can breed continuously, meaning that there is no seasonal start or finish.
So that is the technical bit, now how can we apply that to improving our breeding results?
We can split the TRIGGERS into KEY AND SECONDARY
So clearly, the first thing we have to do is determine where our birds originate from. If they originate near the equator and circa 75% of them do, then clearly they are not going to be heavily influenced by increasing the hours of light above 12 hours.
Conversely, the further from the equator your birds originate, the more heavily they are going to be influenced by day length.
So to look at Australian species, those which originate from near Darwin will get around 12.75 hours daylight in Summer and 11.5 hours daylight in winter, a difference of only 1.25 hours. So clearly, although light may have an effect, you would not expect it to be huge.
Conversely, the species which originate in Tasmania get approximately 15 hours of daylight in summer and 9.25 hours in winter. A difference of 5.75 hours of daylight, so obviously this could be significant.
Interestingly if you live in Scotland, UK, the difference in daylight hours between summer and winter is 10 hours, so if one was trying to breed birds which originated from there, managing the daylight hours of these birds would be very important.
By using electric lighting, aviculturists can manage light artificially. If we keep birds which in the wild breed when daylight length is 15 hours and we live in a tropical zone where daylight length is about 12 hours, then increasing the hours of light to 15 hours would probably improve your breeding results.
Conversely, if the species of birds you keep originate from somewhere near the equator, increasing the photoperiod would be less likely to benefit.
So in other words, matching the photoperiod to that of where your birds originate from could improve your breeding results.
The next on our list of KEY TRIGGERS is nutrition.
Extended photoperiod and/or rain induces plants to fruit and seed; insects are also stimulated to start their breeding cycles, improving not only the volume of food but also its nutritional value.
For birds which originate from near the equator, it is likely that food, often driven by rainfall patterns, is the largest single factor in bringing birds into breeding condition whilst it will have a conjoint influence with temperate birds which of course also rely on light for stimulation.
Birds which originate from hostile environments like the deserts will not require as high a nutritional improvement to bring them into breeding condition as birds which live in rich environments.
Zebra Finches for example are highly adapted to live in really poor and unpredictable habitats. One important adaptation to overcome the lack of water is that Zebras can recycle their urea, whilst some like the Gibber Bird do not need water at all as they can extract enough moisture from insects to stay alive.
In captivity we may have been overfeeding Zebras. To instigate AUSTERITY and stop them producing sperm and ovulating, they have to be fed on nutritionally poor grass seeds and then possibly only need a standard dry finch seed mix and a small amount of supplement to bring them into breeding condition.
Conversely, in the wild the Crimson Finch lives in the food rich riparian zone along permanent water in the creek beds and so do not lose as much condition during the AUSTERITY period as say the Gouldian and Longtailed Finch which live in the same region, therefore Crimsons require a measurably richer diet to bring them into breeding condition.
Seasonal temperatures can be a breeding trigger.
Scientists have recorded earlier onset of breeding in Great Tits when spring temperatures were higher than norm.
So unseasonable early spring temperatures can trigger earlier breeding.
If it is too cold, plants and insects will not reproduce and the amount of energy required just to keep warm is high.
Scientists have recorded that low temperatures may also lead to smaller eggs, and
nestlings produced during these colder months have to be brooded for longer and face a shorter day so there is less time to feed, therefore fatalities would be higher. Also surviving nestlings tend to be smaller and weaker.
Most birds will therefore not be triggered into breeding during the cold months.
In captivity, the provision of too rich a diet during the cold months may confuse the endocrine system and stimulate the production of gonadotropin hence triggering unseasonal breeding.
Conversely, if it is too hot, the males cannot produce sperm or much of the sperm will be malformed and so once again breeding will stop.
Interestingly, if the nights are cool, the males will produce sperm overnight and mate with the females in the early morning.
Heat can also herald the start of the dry season and a reduction in food supply and water which of course would inhibit breeding.
Although the factors that make a pair compatible are not well understood, it is well documented that incompatible pairs either do not manage to breed successfully or produce very poor results.
Interestingly, in the wild most species choose their partners when they are juveniles or sub adults. This makes sense of course because they need to be ready to maximise the amount of breeding time they have once conditions become favourable. With some species, by the time they found a mate, competed for a territory, found a nest site and built a nest, the breeding opportunity might have finished!
COURTSHIP / NESTING SITE
Generally the male comes into breeding condition before the female who requires the stimulus of the courtship behaviour and the availability of a suitable nesting site and nesting material, to finish bringing her into breeding condition.
FACTORS INFLUENCING POOR BREEDING RESULTS
GnIH, is the neurohormone which stops breeding by providing negative feedback to the pituitary gland.
Stress triggers the production of GnIH which then inhibits the production of the
gonadotropins FSH and LH, which of course therefore brings breeding to a close or prevents it from starting in the first place.
Stress can also trigger the production of the hormone Corticosterone which
interferes with the production of the breeding hormones.
In the wild, stress can be caused by a number of factors, short photoperiod, high temperature, low temperature, poor diet; in fact, the reverse of all the triggers which stimulate breeding.
In captivity, there can possibly be additional items creating stress, like overcrowding, bad aviary set up, wrong nesting sites, disruptive aviary inhabitants, or threats from outside (hawks, noisy miners etc.).
Failure to brood eggs and / or raise the nestlings can largely be laid at the door of the hormone Prolactin, or more to the point, the lack of it. Corticosterone caused by stress is often associated with this condition.
Prolactin contributes to the process of incubation and the creation of a brood patch whilst providing negative feedback to the pituitary to suspend the production of LH and FSH hormones which stops the birds from producing more eggs or nest building instead of incubating.
It is stimulated by the production of eggs and the hatching and feeding of the nestlings.
A failure in the production of Prolactin leads to the parents abandoning the eggs or nestlings which can then either start the onset of a new laying cycle or may even bring breeding to a halt.
The external stimuli which cause the changes to the secretion of hormones of course are probably the ones discussed above.
Nature is a wonderful thing and produces many variations to accepted norms. So although the above information is largely correct for most of the birds kept in aviculture, there are of course variations. Males of species which do not share in the brooding process are unlikely to be stimulated to form a brood patch. And in some species it is not always the female who takes on the responsibility for brooding and rearing the nestlings; the Comb Crested Jacana female will copulate with a number of males and leave them all with eggs they have to hatch and rear. Maybe in revenge, Bower Bird males will copulate with as many females as he can entice into his bower, but concludes that is the end of his responsibilities!
And of course, around the world there will be even more variation.