Crested geckos (Correlophus ciliatus) are popular pets admired for their unique head crests and wide variety of colors and patterns, known as morphs. A fascinating biological feature of these animals is their ability to rapidly change the intensity of their coloration. This shift in hue is a normal, temporary process, responding to their internal state and external environment rather than serving as camouflage.
The Mechanism of Firing Up and Firing Down
The process of a crested gecko changing color is commonly referred to as “firing up” or “firing down.” Firing up describes the state where the gecko’s colors and patterns become darker, richer, and more saturated. Conversely, “firing down” is when the colors lighten and appear paler, sometimes taking on a dull, grayish, or pastel tone.
This rapid color change is powered by specialized pigment cells located in the skin called chromatophores. These cells contain pigment granules, particularly melanin, which is responsible for dark coloration. When the gecko fires up, these pigment granules disperse and spread out across the cell, maximizing the visibility of darker colors.
To fire down, the gecko contracts the pigment granules back into a tight cluster near the center of the chromatophore. When the granules retract, less pigment is visible on the skin’s surface, causing the appearance to lighten and become duller. This physiological mechanism allows the gecko to shift its color intensity quickly, often over minutes or hours. The shift is a response to specific cues, not a conscious choice by the gecko.
Environmental and Behavioral Triggers for Color Shifts
A variety of external and internal factors prompt the crested gecko to transition between the fired-up and fired-down states. A primary driver is the daily light cycle, as these geckos are nocturnal. They typically fire up when it is dark and they become active, allowing their darker coloration to blend into shadows.
During the day, when they are sleeping and exposed to light, they naturally fire down and display lighter colors. This pattern is a reliable indicator of the gecko’s activity state. Environmental conditions such as humidity and temperature also play a role in triggering color shifts.
Higher humidity levels, often reaching 70% or more, can cause the gecko to fire up. This state is frequently observed after misting or during the night when humidity is naturally higher. Conversely, low humidity and lower temperatures often correlate with a fired-down state.
Behavioral or emotional states also influence the color transition, as the shift is mediated by the nervous system. Excitement, such as during feeding or hunting, can cause a gecko to fire up quickly. Stress or fear, such as being handled, can also trigger a rapid firing up.
Distinguishing Permanent Coloration from Temporary Changes
While the daily firing cycle is a temporary color shift, crested geckos also experience changes related to longer-term biological processes. Ontogenetic change refers to the permanent development of color and pattern as a gecko matures from a hatchling to an adult. Juveniles often look different from their adult coloration, with patterns and colors intensifying or changing significantly over the first year of life.
A common temporary change that can concern owners is the dull, pale appearance just before the gecko sheds its skin. When preparing to shed, the gecko’s colors become noticeably grayish, pale, or dull, which can be mistaken for a severe fired-down state. This pre-shed dullness is a natural part of the skin-replacement process. It resolves entirely once the gecko has successfully removed its old skin, often leaving behind a brighter appearance.
In rare instances, non-reverting color changes can indicate a health issue rather than a normal firing or shedding cycle. For example, extreme paleness that does not resolve with proper husbandry, or unusual dark spots limited to areas like the tail or toes, may be signs of dehydration, illness, or necrosis. These concerning changes are distinct from the natural, reversible shifts that occur daily.