Crocodylus palustris (Lesson, 1831)

Introduction

Crocodylus palustris, commonly called the mugger crocodile, has the following physical characteristics.

Coloration

Hatchlings are pale olive with black spots, while adults range in color from dark olive to grey or brown.

Head and Neck Scutes

Its head is rough with no ridges, and it has large scutes around the neck that are well separated from the back.

Body Scute Arrangement

Scutes typically form four longitudinal series, rarely six, and 16 or 17 transverse series.

Limb Structure

Keeled scales cover its limbs, with serrated fringes along the outer edges of the limbs, and the outer toes are extensively webbed.

Snout and Teeth

Its snout is slightly longer than it is broad, with 19 upper teeth on each side.

Jaw Bone Structure

The symphysis of the lower jaw extends to the level of the fourth or fifth tooth.

Palate Bone Structure

On the palate, the premaxillary suture is nearly straight or curves forward, and the nasal bones separate the premaxilla above.

Snout Distinctiveness

The mugger crocodile is a medium-sized crocodilian, and has the broadest snout of any living crocodile species.

Sensory and Locomotor Adaptations

It has a powerful tail and webbed feet, with acute vision, hearing, and sense of smell.

Adult Length Range

On average, adult females measure 2 to 2.5 m (6 ft 7 in to 8 ft 2 in) long, while adult males usually measure 3 to 3.5 m (9 ft 10 in to 11 ft 6 in); individuals rarely reach 5 m (16 ft 5 in) long.

Largest Recorded Lengths

The two largest known mugger crocodiles, both measuring 5.63 m (18 ft 6 in), were killed in Sri Lanka.

Bite Force

One 207 kg (456 lb) individual had a recorded bite force of 7,295 N (1,640 lbf).

Male Weight Range

Large males may reach a weight of 450 kg (1,000 lb).

Museum Specimen Size

The largest zoological specimen held at the British Museum of Natural History measures 3.7 m (12 ft 2 in) long.

Pakistan Specimen Measurement

One approximately 3 m (9 ft 10 in) long male caught in Pakistan weighed 195 kg (430 lb).

Geographical Range

The mugger crocodile is found in southern Iran, Pakistan, Nepal, India, and Sri Lanka, up to an elevation of 420 m (1,380 ft).

Preferred Habitat Types

It inhabits freshwater lakes, rivers, and marshes, and prefers slow-moving, shallow water bodies.

Artificial Habitats

It also thrives in artificial reservoirs and irrigation canals.

Iran Distribution

In Iran, it occurs along rivers in Sistan and Baluchestan Provinces near the Iran-Pakistan border.

Iran Population Size

Around 200 mugger crocodiles live on the Iranian Makran coast near Chabahar.

Iran Population History

Human activity and a long drought in the late 1990s and early 2000s pushed this population to the brink of extinction, but much of its habitat was restored after tropical cyclones in 2007 and 2010 flooded formerly dry lakes and hamuns.

Pakistan Dasht River Population

In Pakistan, a small population lives in 21 ponds around the Dasht River; 99 individuals were counted in the winter of 2007–08, and by 2017 the population had declined to 25 individuals.

Pakistan Sindh Province Distribution

In Sindh Province, small populations live in the wetlands of Deh Akro-2, Nara Desert Wildlife Sanctuary, near Chotiari Dam, in the Nara Canal, and around Haleji lake.

Nepal Distribution

In Nepal's Terai region, it occurs in the wetlands of Shuklaphanta National Park, Bardia National Park, Ghodaghodi Tal, Chitwan National Park, and Koshi Tappu Wildlife Reserve.

India Distribution

In India, it occurs along the Chambal, Ken, and Son Rivers in Rajasthan, and in Ranthambore National Park; along the Vishwamitri River, and in several reservoirs and lakes in Kutch, Gujarat; in National Chambal Sanctuary, Madhya Pradesh; in Rajaji National Park, Corbett Tiger Reserve, and Lansdowne Forest Division, Uttarakhand; in Katarniaghat Wildlife Sanctuary and Kishanpur Wildlife Sanctuary, Uttar Pradesh; in Simlipal National Park, and along the Mahanadi and Sabari Rivers, Odisha, where 82 individuals were recorded in Simlipal National Park's river systems in 2019; in Manjira Wildlife Sanctuary, Telangana; along the Kadavi and Warna Rivers, and along the Savitri River in Raigad District, Maharashtra; in Salaulim Reservoir, the Zuari River, and small lakes in Goa; along the Kaveri and Kabini Rivers, in Ranganthittu Bird Sanctuary, Nagarhole National Park, and Tungabhadra Reservoir, Karnataka; in Parambikulam Reservoir and Neyyar Wildlife Sanctuary, Kerala; and at Amaravathi Reservoir, and along the Moyar and Kaveri rivers, Tamil Nadu.

Sri Lanka Distribution

In Sri Lanka, it occurs in Wilpattu National Park, Yala National Park, and Bundala National Park; between 1991 and 1996, it was recorded at an additional 102 localities.

Bangladesh Extirpation Status

Historically, it was present in the northern parts of the Sundarbans in Bangladesh, where four to five captive individuals survived in an artificial pond by the 1980s; it is possibly locally extinct in Bangladesh.

Bhutan Population History

It became extinct in Bhutan in the late 1960s, but a few captive-bred individuals were released into the Manas River in the late 1990s.

Myanmar Extirpation Status

It is considered locally extinct in Myanmar.

Aquatic Locomotion

Mugger crocodiles are powerful swimmers that use their tail and hind feet to move forward, change direction, and submerge.

Terrestrial Locomotion

They belly-walk, with their belly touching the ground, along the bottom of water bodies and on land.

Dry Season Behavior

During the hot dry season, they walk over land at night to find suitable wetlands, and spend most of the day submerged in water.

Cold Season Behavior

During the cold season, they bask on riverbanks, and individuals tolerate one another during this period.

Territoriality

Territorial behaviour increases during the mating season.

Thermoregulation Requirements

Like all crocodilians, the mugger crocodile is a thermoconformer with an optimal body temperature of 30 to 35 °C (86 to 95 °F).

Lethal Temperature Thresholds

It risks death from freezing when exposed to temperatures below 5 °C (41 °F), and from hyperthermia when exposed to temperatures above 38 °C (100 °F).

Burrow Use

It digs burrows to retreat from extreme temperatures and other harsh climatic conditions.

Burrow Dimensions and Structure

Burrows are between 0.6 and 6 m (2.0 and 19.7 ft) deep, with entrances located above the water level and a chamber at the end large enough for the crocodile to turn around.

Burrow Temperature Range

The temperature inside the burrow remains constant between 19.2 to 29 °C (66.6 to 84.2 °F), depending on the region.

Sexual Maturity

Females reach sexual maturity at a body length of around 1.8–2.2 m (5 ft 11 in – 7 ft 3 in) at approximately 6.5 years of age, while males reach sexual maturity at a body length of around 2.6 m (8 ft 6 in).

Courtship Timing

The reproductive cycle begins as early as November at the start of the cold season, with courtship and mating.

Nest Construction

Between February and June, females dig 35–56 cm (14–22 in) deep nesting holes between 1 m and 2,000 m away from the waterside.

Egg Clutch Size

They lay up to two clutches, each holding 8 to 46 eggs.

Egg Weight

Eggs weigh an average of 128 g (4.5 oz).

Egg Laying Duration

Laying a single clutch usually takes less than half an hour.

Nest Closure

After laying, females scrape sand over the nest to close it.

Male Parental Care Pre-Hatching

Males have been observed assisting females with digging and protecting nest sites.

Hatching Timing

Hatching occurs two months after laying: between April and June in southern India, and between August and September in Sri Lanka.

Post-Hatching Parental Care

Females excavate the hatchlings, carry them in their snouts to the water, and both females and males protect the young for up to one year.

Viable Incubation Temperature Range

Healthy hatchlings develop at an incubation temperature range of 28–33 °C (82–91 °F).

Sex Determination Factors

The sex ratio of hatchlings depends on incubation temperature and how much sunlight the nest receives.

Temperature-Dependent Sex Ratios

Only females develop at constant temperatures of 28–31 °C (82–88 °F), and only males develop at a constant 32.5 °C (90.5 °F).

Transitional Temperature Sex Ratios

The percentage of females in a clutch decreases at constant temperatures between 32.6 and 33 °C (90.7 and 91.4 °F), while the percentage of males decreases at constant temperatures between 31 and 32.4 °C (87.8 and 90.3 °F).

Natural Nest Temperature Variation

In natural nests, temperatures are not constant and vary between day and night.

Early Nest Sex Ratios

More females hatch in early natural nests, when initial temperatures inside the nest range between 26.4 and 28.9 °C (79.5 and 84.0 °F).

Late Nest Sex Ratios

The percentage of male hatchlings increases in late nests located in sunny sites.

Hatchling Size

One-month-old hatchlings are 26–31 cm (10–12 in) long and weigh an average of 75 g (2.6 oz).

Juvenile Growth Rate

They grow approximately 4.25 cm (1.67 in) per month, and reach a body length of 90–170 cm (35–67 in) by two years of age.

Tool Use for Hunting

Mugger crocodiles have been documented using lures to hunt birds, making them among the first reptiles recorded to use tools.

Lure Hunting Method

They balance sticks and branches on their heads to lure birds searching for nesting material.

Lure Hunting Effectiveness

This strategy is particularly effective during the bird nesting season.