Breeding: H. regilla breeds over a long period of time, from January to the middle of May, in marshes, ponds, lakes, reservoirs, roadside ditches, and slow streams (Stebbins 1985). In interior British Colombia, it may breed in June and July also. Later breeding occurs in higher altitudes. Around January, at the beginning of the breeding season, large numbers of vociferous males congregate at transient rain pools and more permanent bodies of water. The females do not enter the water until later, when they are ready to lay. Usually, females enter in the late afternoon or early evening, and mating and egg laying usually occurs by the following morning. Females enter either by themselves or in small groups, so there are many more males than females, making immediate mating probable. Usually, there is a preliminary period of clasping that lasts anywhere from 4 to 24 hours in a laboratory, and probably about 4 to 10 hours in nature. The male tightly grips the female with is forelimbs, but does not contact her with his body behind his pectoral region except when inseminating eggs. The male’s legs are flexed in a sitting pose, and insemination occurs at the moment of the extrusion of the eggs. The male discharges a quantity of transparent semen by bringing his cloacal aperture close to that of the female. With a quick, firm extension, the male slides his feet posteriorly over the sides and hips of the female, then retracts to his previous position. Simultaneously, the female extrudes a clutch of eggs into the cloud of sperm. The female sometimes scratches the substratum on which the eggs are going to be deposited before releasing the eggs. As the female extrudes the eggs, her cloaca is brought close to this surface and their attachment is effected. The eggs may be removed from her cloaca by her tarsi through flexor-extensor reflexes. The interval between layings is usually 2 to 10 minutes, but could be longer. After oviposition, the frogs separate. Amplexus is pectoral, and may last from 8 to 40 hours or longer (Smith 1940).

Eggs: Clusters of eggs are deposited in a pond’s shallow water, usually at depths above 4 inches. The clusters can be attached to sticks, leaves, vegetation, or other objects, and they can also be found floating on the surface, usually attached to objects. Eggs are usually laid in loose clusters of irregular shape, and the cluster has 2 gelatinous envelopes. The outer envelope is 4.78 to 6.7 mm and is sticky, and the inner envelope is 1.88 to 2.70 mm. Each packet usually has 22 to 25 eggs, but could have anywhere from 5 to 60 eggs. As the layings near an end, the number of eggs per clutch can decrease to 3 or 4, or even single eggs (Livezey and Wright 1947).

Larva: The tadpole is about 45 mm long, full and deep-bodied, and has a fairly long tail, about 2 times the head and body length. The labial tooth row formula is 2/3, and the spiracle is sinistral, directed posteriorly (Grismer 2002). The general color is blackish and yellowish brown to dark brown with heavy black spots. Below, it is whitish with bronze or copper tinges. The tail is mottled with black, and the iris is golden, with a darker area anterior and posterior to the pupil (Stebbins 1951).

Call: H. regilla is the most commonly heard frog species on the Pacific coast. The calls last for about 1 second and are often uttered in sequence. Each 1-second call consists of a loud, two-parted 'kreck-ek', with rising inflection in the last syllable. H. regilla has a round vocal sac (Stebbins 1985). While singing, a male may float with his limbs outstretched and his globular pouch extended to or beyond his chin (Stebbins 1951).

Food: H. regilla eats insects, including leaf-hoppers, spring-tails, flies, stoneflies, ants, wasps, beetles, and caterpillars, It also eats spiders, isopods, and snails (Stebbins 1972).

Behavior: H. regilla is mainly nocturnal, but it is also active in the daytime. Sometimes, at low elevations, it is active throughout the year. It is a good climber, but usually stays near the ground. It has a great capacity for color change, and a change from an unspotted dark coloration through a medium light colored phase with spots to an unspotted light phase may take about 8 to 10 minutes (Stebbins 1951).