Authored by Ron Tremper Leopardgecko.com
BREEDING LEOPARD GECKOS | Aggression
On male aggression and territoriality
One of the mantras of leopard gecko keeping is that you cannot keep mature males together or they fight and inflict serious injuries to each other. This is true in captivity and good advice, however other factors play a contributing role in aggressive and territorial behaviors of males. For example, males raised together from babies without exposure to females may cohabit peacefully for a long time. A hypothesis of hobbyists supported in part by research is that male aggression is increased by the presence of females. In one study (Sakata et al., 2002) males that had been kept with several females for one to two years had more elevated testosterone levels than naïve males raised singly. These experienced males were also more active and expended more effort in marking their territory. A sure way to elicit male aggression is to introduce an additional male to an established breeding group.
Another factor worth considering is kinship, as detected by smell. In Patrick Huddleson’s experiment to allow babies to hatch and be raised in the same tank (standard 36 inch long) as their parents, the colony grew to 10 animals including 3 mature males. According to Huddleson (pers. comm.) subdominant males learned to avoid the alpha male keeping out of his way and resting outside of the main shelter. However, he had to remove additional males as they matured because signs of aggression were noted. We already know that leopard geckos, as long as they are not starved tend not to cannibalize juveniles but the possibility that members of a colony are recognized by scent needs to be further investigated.
On female aggression and territoriality
One does not have to house leopard geckos in breeding groups long before the keen observer will notice that something is going on between females when more than one are housed together. There is a definite hierarchy amongst captive females. The matriarch or alpha female dictates her close presence to the male at hand, dominates the best heat source if that source is too small, and often will attack any newly introduced females by violently grasping their tail. Make sure you monitor your geckos anytime a new female is introduced. It may take several attempts for the other females to accept her. Keep trying.
Keepers will find that the less you disturb or change the dynamic of a particular breeding group, the less female aggression will be seen. Pairing up breeding groups before geckos reach sexual maturity or introducing larger animals into a new cage all at the same time is a beneficial first choice to avoid such problems.
Introductions
The first time one witnesses leopard geckos fighting can be a disturbing experience, particularly for novices. By using some common sense procedures, introducing one or more geckos to an enclosure with others can be done safely. The first two points to consider are:
Are you putting two males together by accident?
Never house more than one male gecko per cage. Adult males of all types of lizards will fight each other. A leopard gecko male will vibrate its tail rapidly when it sees another gecko. If the other gecko in turn vibrates its tail in the same fashion then each of them knows they are confronting another male and a fight will usually follow. If, however, a male signals his presence via tail shaking and the other gecko does not respond in like fashion, then the male knows that the gecko near him is either a female or an immature gecko.
Is there a major size difference between the geckos you want to house together?
Size does matter. Avoid placing geckos of different sizes together for breeding purposes. Doing so can result in stress for the smaller individual, possibly injury, or even death.
One approach to avoid the stress of sudden introductions is to set up adolescent female groups well in advance of their reaching sexual maturity and then not changing the composition of the group unless absolutely necessary. Allowing 2-6 individuals to grow up together, then adding a male when they reach 9-10 months of age, results in a healthy group compatibility that rarely produces confrontations.
A common scenario involves wanting to introduce a new gecko in a cage housing a long-term captive. Geckos of either sex are territorial when suddenly faced with what they perceive as an intruder in their previously solitary world. Always supervise such introductions. The risks of aggression are reduced if both geckos are introduced in a new cage at the same time.
It is best not to handle resident animals just before placing one or more new geckos into their cage since the handling tends to make them defensive and over reactive towards new cage mates. If some type of aggressive behavior is going to occur, it usually happens within the first minutes of such an encounter. Chasing, tail wagging, biting, but not holding on, and vocalizations are acceptable reactions by either party. However, if one gecko bites the other and holds on with no sign of letting go, then you must intervene by picking up both geckos at the same time and waiting for one to let go. If the situation looks urgent you can hold the gecko’s head under running water and/or lightly thump his head with your index finger. Don’t be dissuaded by these initial reactions, another attempt can be considered in a week.
Some males are real gentlemen when it comes to the females around them and other individuals may always be aggressive by nature. The easiest introduction occurs when a female is joined by another female.
Breeding Part 5 will be presented in the next edition of Tremper’s Corner.