In the first months of 2020 wild pigs caused significant damage to orchards and crops at Horizon Guest House. The pigs, who live in the surrounding forest of McCandless Ranch, were in the habit of making regular raids on our property. Our gardening efforts, and attempts at protection, were left in disarray as they carved a trail of destruction.
Unfortunately, feral pigs on the Big Island of Hawaii have become a widespread problem. Wild pigs are attracted to a wide variety of food sources. On the Big Island these include crops such as macadamia nuts, bananas, avocados and pineapples. Our banana and pineapple plants were almost all destroyed over a period of months. Significant rooting damage was also done to the garden.
Where did the pigs come from?
It was originally thought that the feral pigs in Hawaii were the direct descendants of those brought to the islands by Captain Cook in 1778. Captain Cook arrived with pigs, chickens and other animals. However, a 2016 study found that most of the feral pigs alive in the islands today are in fact the descendants of those introduced by Polynesians in approximately 1200 AD. [1]
That the origins of the feral pigs are not solely European will be helpful for future discussions about conservation on the islands, as well as their role in Hawaiian cultural heritage.
Impact on forest ecosystems
Wild pigs also have an impact on the forest ecosystem. A study by the University of Hawai’i found that soil macroinvertebrate communities (organisms that do not have a spine but can be seen with the naked eye, such as snails and insects) remained unaffected by the presence of feral pigs in the environment.[2] However, earthworms and beetles may benefit from association with sites rooted by wild pigs.
Another study found that the absence of feral pigs over time led to increased bacterial diversity in the soil and that there was an overall increase in the ‘ecological resiliency’ of the soil.[3]
How to combat feral pigs
Pigs don’t like dogs and will tend to avoid an area if they sense or smell their presence. Culling the invading pigs is also another option, but in the case of Horizon this won’t stop the arrival of more pigs as they breed at such a rapid rate in the adjoining forest. The feral pigs are resourceful and have found creative ways of digging under the boundary fence in order to gain access.
Instead we decided on a new approach. We fenced a section of the garden off completely. This area, currently housing the existing vegetable garden, will now also be where we grow the crops most vulnerable to pig invasion. New banana and pineapple plants have been planted and the existing vegetable garden has been expanded. The fence itself has been engineered to be as pig-proof as possible. Additional fence posts have been positioned close together to ensure that the fence is as tight as possible and therefore difficult for even the tiniest of pigs to burrow under.
Feral pigs might appear to be cute and relatively harmless but they continue to cause problems on the Big Island as their numbers in populated rural areas continue to rise. Creative solutions are the best way to try to mitigate their impact on a local level, while perhaps a concerted effort on a state level is needed to combat the issue further.
References
Linderholm A., Spencer D., Battista V., Frantz L., Barnett R., Fleischer R.C., James H.F., Duffy D., Sparks J.P., Clements D.R., Andersson L., Dobney K., Leonard J.A. & Larson G. (2016). [1] A novel MC1R allele for black coat colour reveals the Polynesian ancestry and hybridization patterns of Hawaiian feral pigs. R. Soc. open sci. 3, 160304. https://doi.org/10.1098/rsos.160304
Wehr, N.H., Kinney, K.M., Nguyen, N.H., Giardina, C.P. & Litton, C.M. (2019). [3] Changes in soil bacterial community diversity following the removal of invasive feral pigs from a Hawaiian tropical montane wet forest. Sci Rep 9, 14681. https://doi.org/10.1038/s41598-019-48922-7
Wehr, N.H., Litton, C.M., Lincoln, N.K. & Hess, Steven C. (2020). [2] Relationships between soil macroinvertebrates and nonnative feral pigs (Sus scrofa) in Hawaiian tropical montane wet forests . Biol Invasions 22, 577–586. https://doi.org/10.1007/s10530-019-02117-3
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