By Mike Fidler
DAYLIGHT HOURS [PHOTOPERIOD]
NUTRITION – FOOD ENERGETICS + NUTRITIONAL VALUE
CLIMATE, TEMPERATURE, RAIN
AVAILABLE NESTING SITES & NESTING MATERIAL
COMPETITION, PECKING ORDER
THE HORMONAL CASCADE
In the wild, the start of the breeding cycle in birds is triggered by day length [photoperiod] in temperate zones, and seasonal rains or vegetative greenness in tropical ones. These primary triggers signal the start of a period of reasonably abundant, more nutritious and reliable food resources, and the better nutrition starts the regeneration and growth of the sex organs [gonads] in most bird species.
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 called FSH hormone, LH hormone, and once laying begins, Prolactin.
These hormones all act on the gonads [sex organs] as follows:
FSH stimulates maturation of the gonads in both sexes and sperm production in males.
LH stimulates ovulation by females and the sex hormones oestrogen and testosterone production in both sexes.
Prolactin induces brooding behaviour and brood patch development, and tells the pituitary to halt production of LH and FSH.
The seasonal decrease of photoperiod or the decrease of rainfall or vegetation greenness triggers the production of the negative feedback hormone GnIH which causes the pituitary gland to stop the production of hormones, reversing the above process, shrinking the ovaries and testes, bringing the breeding season to a close, often signalling the onset of a natural austerity [refractory period]period when food supply or quality may be severely reduced.
The above applies to the majority of species, however not all austerity periods are equal, for some the refractory period can last three to four months, for Quelea it is as short as six weeks, but a few have adapted to different triggers, and some, 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 PRIMARY 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 approximately 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 daylength.
So to look at Australian species, those which originate from near Darwin will get approximately 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 a small effect, it cannot be huge.
Conversely, the species which originate in Tasmania get circa 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 approximately 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 unlikely to benefit.
So in other words, matching the photoperiod to that of where your birds originate from could improve your breeding results.
So the next on our list of primary triggers is nutrition.
Extended photoperiod and/or rain induces plants to fruit and seed; insects are also stimulated to start their breeding cycle, 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 arid, seasonally poor habitats. To overcome the lack of water they can recycle their urea, whilst some like the Gibber Bird can extract enough moisture from insects to stay alive.
In captivity we may have been overfeeding Zebras. It is known that to stop producing sperm they have to be fed on nutritionally poor grass seeds and then possibly only need a standard dry finch seed mix to bring them into breeding condition.
Conversely, in the wild the Crimson Finch lives in the food rich riparian habitat along creek beds and so do not lose as much condition during the austerity period as say the Gouldian and Longtail finches do, but require a measurably richer diet to bring them into breeding condition.
Clearly these finch species have very different physiology in relation to their nutritional requirements for breeding.
Rising seasonal temperatures can be a significant breeding trigger. Experiments by Visser et al showed that even a rise in mean temperature of just 4C can induce breeding in Great Tits.
So unseasonable early spring temperatures can trigger earlier breeding.
If it is too cold plants and insects will not be growing or breeding and the amount of energy required by birds just to keep warm is high.
Any nestlings produced during these colder months face a shorter day so there is less time to feed and will require longer and closer brooding therefore fatalities would be higher and 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 gonadotrophin hence triggering unseasonal breeding.
Conversely, if it is too hot, the males cannot produce sperm and so once again breeding will stop.
Interestingly, during these hot periods, if the nights are cool, the males can produce sperm overnight and mate with the females in the cool early morning.
But heat can also herald the start of the dry season and a reduction in food supply 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 often 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.
It is therefore important to try and understand what each species nesting requirements are as few birds nest in the same position or situation and use exactly the same kind of nest building materials.
FACTORS INFLUENCING POOR BREEDING RESULTS
GnIH, is the neurohormone which regulates breeding by providing negative feedback to the pituitary gland
Stress triggers the production of GnIH which then inhibits the production of gonadotropins FSH and LH hormones, which of course therefore brings breeding to a close or prevents it from starting in the first place.
In the wild, stress can be caused by a number of factors: short photoperiod; high temperature; low temperature; poor diet. In fact, these are all the reverse of 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, 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.
Prolactin contributes to the process of incubation and the creation of a brood patch whilst providing negative feedback to the pituitary to stop the production of LH and FSH hormones which stops the birds from producing more eggs 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 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.
Now all this sounds pretty complicated, but once you get your head around it, it’s really pretty simple and for sure, understanding how the hormone flows are triggered definitely helps you analyse and improve your breeding results.
It also becomes more obvious that if we fall into the trap of feeding the same diet all the year round, it is going to be more difficult to trigger your birds into breeding. This is the basis of the use of an austerity period for effectively managing breeding birds in captivity. I have found it very effective over the years, but lamentably many breeders miss the opportunities.
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