It is a sad fact that a great many herps kept in captivity are never bred. I find this saddening because there can be no better way of measuring how well they are being kept than to succeed in breeding them, and to do so repeatedly while maintaining the animals in good health. Certainly, this is my measure, and if I should fail with any species (assuming that I have at least a pair of course!) then my initial assumption is that the problem is a husbandry issue i.e. it is MY fault. After all, the urge to reproduce is one of the strongest in all living things. If this entirely natural driving desire is not realised then it is us, the keepers, who are at fault.
Another important issue is that almost all the wild animals in the world are under increasing pressure for their very survival. There is no doubt that the animal trade has contributed to this pressure - in some cases massively so. This situation, so far as herps are concerned, has improved dramatically and is continuing to improve. This is not due to a lessening in demand for animals, in fact the opposite is the case, but due to the fact that the majority of the trade is now met by captive bred animals. If each and every herp keeper were to breed their animals then we could reduce this trade to virtually zero thus contributing, albeit in a roundabout way, to their conservation.
Breeding triggers. Almost all herps are triggered into breeding by some sort of seasonal change. With most of the species I keep this particular change is the onset of Spring after a winter period which the animals have spent either totally dormant (hibernation), dormant with occasional activity (brumation) or simply a period of reduced activity. For animals which experience these seasonal and corresponding behaviour changes this is absolutely essential as the "rest" period is the time during which sperm and ova are produced and the raising temperatures of Spring trigger the breeding behaviour. Almost any species which originates outside the area encompassed by the Tropics of Cancer and Capricorn will experience this form of seasonal variation.
Within the tropics the triggers are a little more variable due to the significant climatic differences. One very common trigger is the wet season often typified by Monsoon conditions. The onset of these conditions will often trigger immediate breeding behaviour in amphibians who need the relatively short period with volumes of standing water for their larvae together with many lizard species which will mate during the wet season with a view to laying their eggs in moist soil immediately thereafter allowing the eggs to incubate and hatch before things get too dry.
Given this, quite apart from general husbandry and feeding to keep the animals in good health it is necessary to recognise the specific breeding trigger and ensure that it is emulated. Where I live, in the South of the UK this is easily emulated for almost all temperate and Mediterranean species and even some sub-tropical ones simply by using outdoor vivaria or unheated greenhouses with UV-transmitting acrylic glazing. Most of the sub-tropical and tropical species are kept in far more artificial environments which although subject to some influence from external weather/seasonal conditions nevertheless need their environment manipulated to more closely match the breeding triggers in the wild.
Examples of some of the different species I keep and their breeding triggers are set out below.
Lacerta vivipara, agilis and viridis. True hibernators for up to 6 months. Increased temperatures and daylight hours of Spring trigger emergence from hibernation with breeding following shortly thereafter.
Podarcis spp, Timon lepidus, Laudakia spp. Brumation for up to 6 months emerging on fine days in the former. In the latter two, no emergence or significant activity but animals often awake. Spring triggers full activity and breeding as above.
Galloti spp, some Uromastyx spp. Remain active throughout the Winter months but at a considerably lower level. Extremes of cooler weather result in periods of dormancy. Still, Spring triggers full activity and breeding as above although in the latter species this can be earlier.
Physignathus cocinchinus, Basiliscus spp. Little temperature differential although there is a drop in the wet season. Accordingly I reduce the heating levels during our winter and increase the humidity levels. Breeding then starts in the winter but if humidity is maintained will continue well into the summer.
Breeding Behaviour. Generally speaking some form of male display is evidenced. This can include some quite dramatic seasonal colour changes. One of the most outstanding examples of this can be seen in Lacerta agilis. In the western subspecies, soon after emergence from hibernation the males, flanks turn vivid green. In Lacerta viridis the males often develop bright blue throats and cheeks. A general strengthening of colour in males in breeding condition can be seen in most species.
In Lacertids, display behaviour often involves the male approaching the female and curving his body around in front of her while compressing it vertically to appear as large (and presumably desirable!) as possible. This movement is carried out with a strange stiff-legged jerky gait. The same behaviour is often adopted between two rival males. Generally, the smaller will make submissive gestures or simply run away. Occasionally a fight ensues between similar sized animals. This is seldom a bloody affair being a sort of wrestling match where each male tries to seize the other's head and demonstrate it is the stronger. The submissive gesture consists of lifting the forelegs from the ground and "paddling" with them. Females often use this gesture to an interested male, almost irrespective of whether or not they are ready to be mated.
In Agamids, despite the apparent huge differences between the tropical arboreal Physignathus and relatively small Mediterranean Laudakia the predominant display is head-bobbing. Males will often find a quite prominent spot, raise themselves up on their front legs and bob their head up and down vigorously - so vigorously that they appear to be doing a series of fast press-ups. In many species this is accompanied by inflating the gular pouch which is often strongly coloured. Similar behaviour is seen in many Iguanids although these often have a dewlap rather than a gular pouch. Once again, the submissive gesture is often a paddling motion similar to that used by Lacertids. Inter male rivalry can be a much more bloody affair though.
Amphibians deserve a brief mention as their main display behaviour is quite well known consisting, as it does, of different forms of calling. It is worth noting that the calls of frogs, toads etc are totally unique within species. In fact, where species identification is an issue this can be resolved by the call.
Obviously, if you have ensured that the right breeding triggers are implemented and that the animals are properly accommodated and cared for you would expect to see these, or the other appropriate behaviours as a presage to mating.