Lowland Paca, Cuniculus paca

Lowland Paca, Cuniculus paca. Photograph taken in the coastal region of Guatemala, March 2020. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California.

The Lowland Paca, Cuniculus paca, is a member of the Cuniculidae family of Ground-dwelling Herbivorous Rodents. The Cuniculidae family consists of a single genus  that has two species. The Lowland Paca is the only Paca species found throughout North and South America. There are five subspecies of Lowland Pacas present throughout its range. The Lowland Paca is known in Mexico as Paca de Las Tierras Bajas and Tepezcuintle.

Lowland Pacas have stout bodies with large rumps and short limbs. Their front feet have four toes while their hindfeet have five, two tiny side toes and three long weight-bearing middle toes, all with thick claws. They have large heads, swollen cheeks, short ears, large dark eyes, and long whiskers. Straight and bristlelike hairs lie flat in their coarse, shiny coat. Unlike other species, they do not have underfur. They are reddish-brown to dark brown in color dorsally, with three or four lines of large white spots extending from head to rump on each side of their body. On some individuals, these spots coalesce into larger spots or stripes. Their ventral side is light brown to white in color. They have a stumpy hairless tail  that is normally hidden beneath their rump hairs. The males are slightly larger than the females averaging from 65 cm (2 feet 2 inches) to 82 cm (2 feet 10 inch) in length and the females are 60 cm (2 feet 0 inches) to 70 cm (2 feet 4 inches). Their tales are 1 cm (0.4 inch) to 3 cm (1.2 inches) in length. They weigh between 6 kg (13 lbs) and 12 kg (27 lbs). Some males can weigh up to 15 kg (33 lbs). Lowland Pacas have large front teeth, a trademark of rodents, and hypsodont (high-crowned) cheek teeth. They have modified zygomatic arches and maxillary bones that produce a call unique to this species. Their maxillaries have concavities, which are coupled with their very broad zygomatic arch to form a resonating chamber. When air is pushed through this chamber, a low rumbling sound is produced.

Lowland Pacas are monogamous, with a pair of adult Pacas mating for life. Each pair inhabits a home range of approximately 3 hectares (7.4 acres). The males establish their dominance over the females and reinforce their pair bond by urinating on the female, who may become aggressive if she is not receptive to the behavior. They may form loose family groups consisting of a male, female, and their offspring. Breeding occurs uniformly year round, likely due to the availability of food year round. A number of studies have been conducted on the reproduction specifics of the Lowland Paca, and the data is very similar. Generally, the estrous cycle of a female lasts approximately 32 days. Gestation lasts around 148 days in the wild and 97 to 118 days in captivity. Some females may undergo 2 birthing events per year, producing one young per event. The time between birthing events is approximately 225 days in captivity and between 172 and 191 days in the wild. Their young are highly precocial, being born fully developed with their eyes open and the ability to eat solid food within a day. Newborn females weigh around 606 g (1 lb 5 oz) and males weigh around 737 g (1 lb 13 oz), with an average length of 23 cm (9.1 inches). They grow quite rapidly, reaching 4 kg (8 lbs 13 oz) in 3 months and 6 kg (13 lbs 3 oz) in 6 months. Parental care is provided by the female, who nurses her young for up to 3 months. Some females care for their young for as little as 8 weeks, while others provide care for over 6 months. The young follow their mothers and learn, or imprint on, her behaviors. Both male and female Lowland Pacas typically reach sexual maturity between 8 and 12 months of age, with most individuals being sexually mature within one year. The Lowland Paca has a live span of twelve and half  years in the wild with an 80% survival rate for the adults.

Lowland Pacas are mostly nocturnal and solitary, living in forested habitats near water, preferably smaller rivers. They dig simple burrows approximately 2 m (6 feet 7 inches) deep, usually with more than one exit. Occasionally, they may live in burrows created by other animals. They are skilled climbers and will climb trees in search of food. Lowland Pacas are frugivores, feeding primarily on fallen fruits, however, they will also consume a variety of plant material including seeds, leaves, and tubers. They typically forage close to their denning grounds and limit their activity to a few small locations. Their home range and activity shifts with fruit availability, and they often change their feeding locations around late August. They prefer high energy foods such as mangos or avocados. They have been known to eat the seeds in addition to the fleshy part of the fruit. During the winter months, between November and March, there is often a food shortage for the Lowland Pacas. This time is believed to be the limiting factor affecting their population sizes. More often than not, their cause of death is being consumed by a predator, but they may be in a weakened state due to lack of food availability. Their population density is often determined by the presence of fruit-bearing trees and the abundance of fruit on the forest floor. Other factors influencing their population density include type of forest, presence of water, availability of denning locations, and the abundance of predators. Lowland Pacas are preyed upon by a number of predators including jaguars, cougars, bush dogs, crocodiles, boa constrictors, and humans. They are excellent swimmers and usually head for the water to escape danger, as they can stay underwater for several minutes. Lowland Pacas, like most mammals, perceive their environment primarily through their auditory and olfactory senses. However, they also possess very advanced visual systems due to their nocturnal lifecycle. They have retinal ganglion cells (major output cells of the retina) and a tapetum lucidum (a special reflective structure) that enhances their vision at night. This allows them to see well in darkness, providing them an advantage over other similar nocturnal species during times of low lunar illumination.

The Lowland Paca live around disturbed habitats, often constructing their burrows around riparian zones near water despite these sites being prone to flooding. In patchy habitat areas, they use undisturbed zones of forest as dispersal corridors. Agricultural plantations of fruit-bearing crops often produce an agroforest environment, which is often adjacent to natural forest. Lowland Pacas, and other forest-dwelling species, use this corridor to disperse across their range.

The Lowland Paca may be confused with the Central American Agouti, Dasyprocta punctata  (smaller weighing up to 4 kg (8 lbs 13 oz), with a slender build, pale orange to brown, grizzled with black, their hind feet have three toes with hoof-like claws).

From a conservation perspective, the Lowland Paca is considered to be of Least Concern due to their wide distribution, presumed large population size, and occurrence in a number of protected areas. However, local extinctions have occurred in the southeast part of its range due to habitat destruction. The Lowland Paca is an important game animal throughout its range and is frequently taken as bush meat. While some studies suggest that there have been signs of population decline due to extensive hunting and habitat loss, others have shown that they are widespread in many protected areas and show no signs of population decline, apart from small pockets. The mixing of agricultural systems, along with primary and secondary forest, has created adequate habitat for Lowland Pacas to currently live. Threats to this species include loss of habitat, forest fragmentation, hunting, and introduction of domestic species.