Invasive Species Control Threatens Endangered Native Birds: The Case of the ‘I’iwi and the Banana Poka

BY SYDNEY ROSS SINGER – It’s not easy being a native bird in Hawaii. And now, as a result of invasive species control, native bird survival is getting even tougher.

The problem is that certain plant weeds are serving as an important food source for some native birds, which have come to rely on the introduced plants for survival. Kill the weeds, and you starve the birds.

Consider the case of the banana poka (Passiflora mollissima). This relative of the passionfruit, or lilikoi, grows as a vine and produces a delicious fruit, grown commercially in some places. Here in Hawaii, the vine escaped cultivation and entered the forests, where it grows into the canopy of trees. Declared a noxious weed by the Hawaii Department of Agriculture, control and eradication efforts have attacked this vine for decades with biocontrol insects, fungus, and herbicides.

While pest controllers comb the forests for banana poka to kill, the native Hawaiian ‘I’iwi bird searches for banana poka to eat. The red plummaged, curve-billed ‘I’iwi bird is now rare on most islands. It is a nectar feeding bird, preferring the o’hia and mamane, but also feeding on nonnative species, especially the banana poka. In fact, the banana poka blossoms at a different time of year than the o’hia and mamane, providing food for the birds at an important time of shortages.

The dogma of invasive species control is that native species of birds only require native species of plants and insects for food. The belief is that native species existed in Hawaii before introduced species came, and therefore they don’t require introduced species for survival.

In reality, however, the native plants and native insects upon which native birds once fed are now themselves rare, and native birds have had to adapt to new food sources for survival. For the ‘I’iwi, this food source includes the banana poka.

In fact, according to the DLNR, the ‘I’iwi diet consists primarily of nectar taken from a variety of native and non-native flowers and the presence of non-native flowers may have contributed to increases in some ‘I’iwi populations. According to the USDA Forest Service, banana poka nectar is a major food source for ‘I’iwi in some areas and has greatly increased density of ‘I’iwi in parts of the Hakalau Forest National Wildlife Refuge on Hawaii.

This means that efforts to control or eradicate the banana poka may also be harming the ‘I’iwi.

So I contacted the invasive species committees, which are actively attacking banana poka throughout our forests with herbicides, and asked what efforts they were taking to mitigate harm to the ‘I’iwi. The response was that, while the loss of banana poka may reduce bird populations, the ‘I’iwi was here before banana poka and can survive without it.

Those are stoic words for a fragile bird population to swallow.

Clearly, the invasive species people want banana poka killed at any price. If native birds have to suffer, then that is an acceptable price to pay to cleanse the environment of this “noxious” food source.

But shouldn’t invasive species control help native species? Isn’t the threat to native species the reason why invasive species are bad? If invasive species control harms native species, why do it?

The obvious reason is that there is money available to kill invasive species, especially using herbicides. The UH CTAHR is currently experimenting with the use of herbicides to kill banana poka and other plants, and has patented a new method for applying the poison in the forests. Trademarked as “Herbicide Ballistic Technology”, herbicide applicators shoot target plants with patented poison pellets from paint ball guns. Our forests are becoming a shooting range in this war on invasives. https://www.ctahr.hawaii.edu/LearyJ/videos/HBTvideos.html

Unfortunately, there is little money to study what this loss of banana poka food supply will do to the ‘I’iwi. Amazingly, little is known about the ‘I’iwi biologically or behaviorally.

For example, one of the research priorities of the DLNR is to, “Conduct life history studies to quantify the population structure, dispersal patterns, survivorship, nesting phenology and success of this poorly known species.” https://www.state.hi.us/dlnr/dofaw/cwcs/files/NAAT%20final%20CWCS/Chapters/Terrestrial%20Fact%20Sheets/Forest%20Birds/iiwi%20NAAT%20final%20!.pdf

The Forest Service states, “Despite its seasonal high densities and wide-spread distribution in higher-elevation forests, no aspect of the ”I’iwi’s life history or biology has been well studied.” https://www.fs.fed.us/psw/publications/4251/fancy2.pdf

If they had studied the ‘I’iwi better, perhaps they would have discovered that destruction of banana poka can expose these birds to disease, as they enter lower elevations looking for food. Avian malaria is carried by mosquitoes at lower elevations, which is why native birds are mostly confined to higher, mosquito-free elevations. This is also where banana poka grows well. Sending the birds on a wild food chase can infect the birds with malaria, a major cause of bird declines in Hawaii.

So here is the dilemma. A vine is choking some trees in the forests, but is also feeding some rare native birds, as well. If you kill the vine, you may save the trees (so long as they survive the poison). But you also may kill the birds relying on the vine for food.

This illustrates one main problem with invasive species control. Native species have come to rely on introduced species. The environment has changed, and those species which have adapted to the change are now threatened by efforts to control or eradicate the introduced species. Meanwhile, research money is spent on new ways to poison things, instead of studying the complex interrelation between native and introduced species.

We also need to question the motivations for invasive species control. Since poisons are the major arsenal for this environmental war, it is clear that the money will be on poisoning first and asking questions later. Chemical company giants like Monsanto and BASF exert great financial influence on UH researchers and administrators, as well as on elected and appointed officials. The invasive species agenda is promoted by these companies. All munitions manufacturers encourage war.

But the war is on our environment and the introduced species that have come to redefine that environment.

The lesson of the ‘I’iwi and the banana poka is that nature is more complex and integrational than the pest controllers imagined. What is a weed to some may be a food to others.

The birds have learned to adapt to introduced species and environmental change. Isn’t it time we do the same?

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