Movement Patterns of the Mongoose in Hawaii

1. What they did

The small Indian mongoose was brought to Hawaii in 1883 and became common there. Mongooses matter for public health, farming and game management, and in the Hamakua District of Hawaii Island they were part of a problem of plague in fleas, rodents and people. Little was known about how far small carnivores move, so the author set out to describe how mongooses use space.

• Trapping. Seven traplines were set along roads, with traps 0.1 mile apart, usually 21 traps in two 1-mile rows crossing each other. Each line was trapped for 4 days every month for 12 to 37 months, from April 1961 to April 1964: 147 traps in all, baited mostly with fresh beef trimmings.
• Marking. Each mongoose was lightly anaesthetised with ether, marked with ear tags and clipped toes, and released where it was caught.
• Measuring movement. Trap sites were plotted on topographic maps. For each animal the author measured the average distance between successive captures (av. D) and the range length between the two farthest capture points, adjusted for trap spacing (adjusted range length, ARL).
• Removal trapping. After marking ended, four lines were trapped out for 22 to 34 days, which recovered 99 marked animals.

2. What they found

Trapping

• 546 mongooses were marked and caught 861 times in 17,766 trap-days: one mongoose for every 20.7 trap-days.
• Mongooses grew wary of traps after being caught. Capture rates fell from one per 7 trap-days in a line’s first month to one per 20 by the eighth month. Mongooses often scratched and dug around traps to reach the bait without going in.
• Every year captures slumped in late summer (August to October), even though many young animals were then fending for themselves. This was seen both in the heavily populated Kaapahu line and in the six lightly populated lines.
• About six males were caught for every four females. In the breeding season (January to July), males made up 77.4% of captures of animals caught more than once.
• 41.0% of males and 37.8% of females were caught again at least once; the average gap between captures was 4.5 months for both sexes.

How far they moved

• Average distance between captures was 1,290 ft for males and 484 ft for females (about 0.25 and 0.10 mile), a significant difference (P < 0.01). Males moved about 2.7 times as far as females.
• Distances were similar across traplines.
• The longer the gap between captures, the farther apart the capture sites, and this increase was greater for males.
• 18.7% of male recaptures and 41.0% of female recaptures were in the same trap as before. Fewer males returned to the same trap as time went on, while females kept returning at about the same rate.
• Adjusted range length averaged 2,184 ft for males (about 0.4 mile) and 1,062 ft for females (about 0.2 mile). Male ranges grew with the number of captures; female ranges grew much less.
• Males’ ranges seldom exceeded 1.0 mile and females’ seldom exceeded 0.4 mile.

Long moves

Only two mongooses moved between distant traplines: a male that moved 2.9 miles in 31 months and a male that moved 5.0 miles in 12.5 months, ending 800 ft higher. A female caught on the Waimea Plain and released at Paauhau was caught again a month later, 4.8 miles away in the direction of where they had first been caught.

3. What they concluded

• The small Indian mongoose is a sedentary animal that rarely disperses, with movements notably restricted even for a small carnivore.
• Males are 1.4 times heavier than females, which may explain why they need more space.
• The small home range seems to go with plentiful cover and a varied, omnivorous diet. Social needs probably shape home ranges too.
• Individual ranges appear to overlap a great deal, which suggests a complex social structure and may rule out strong territoriality, though whether the species is territorial is uncertain.
• The single displaced female suggests a strong homing instinct.
• If daily range is about the same as av. D, the maximum range is about four times the daily range.
• The trap spacing may have been too wide to measure female ranges well. Even so, trapping only 4 days a month over 3 years avoided animals getting used to traps, and long-term data like these could not have been gathered in any other practical way.

6. Other technologies, skills or innovations

• Ear tags combined with toe clipping for marking individuals.
• Four trap types: commercial live traps, a home-made hardware-cloth trap, and unbaited steel traps set beside cage traps (steel traps only during removal trapping). The home-made trap’s door caught some animals across the neck or back, killing five.
• Distances measured by car odometer and topographic maps.

7. Implications for conservation (from the paper)

• The study was designed to help understand the mongoose’s place in the spread of plague among fleas, rodents and people in the Hamakua District.