Post 5

Editor’s Note: This is the fifth in a six-part series

AT HIGH altitude, relatively few malaria-bearing mosquitoes are able to survive in the cool air — but with predicted temperature changes, the insects can expand their range, adding new pressures to the island’s disease-susceptible bird populations. 

Native forest birds in the Hawaiian Islands have adapted to life at higher elevations over the past 30 years. With no natural protection against diseases such as avian malaria (Plasmodium spp.), susceptible birds are provided with ‘disease-free’ strongholds at higher elevations where the temperatures have historically been too low for the survival of the malaria parasite and the disease-carrying mosquitoes which like warm and wet conditions. Put in other words, how cold it is limits the distribution and population sizes of malaria-carrying mosquitoes, and thus of many Hawaiian birds.

In Hawaii, more than 20 forest bird species live on cool, high elevation mountains — above 4000 ft — such as Puu kukui (shown above) where mosquitoes don’t thrive. However, a warmer climate is enabling these diseases to spread, as malaria-bearing mosquitoes are no longer being killed by prolonged winter cold.

Given the threat of climate change, these mosquitoes will likely creep up the volcanoes, bringing their parasitic passengers along for the ride. So as malaria rises up slope, the amount of disease-free refuge will shrink. And of course, this would have a devastating effect on populations of honeycreeper, and other native forest birds as well.

“Without question, the one factor that prevented widespread and rapid extinction of virtually all of Hawaii’s native honeycreepers after the introduction of avian malaria was the presence of high-altitude disease refuges on Kauai, Maui and Hawaii,”

Dr. Carter Atkinson, a U.S. Geological Survey (USGS) microbiologist based at the USGS Pacific Islands Ecosystems Research Center in Hawaii.

High elevation areas have served as "refugia" on Kauai, Maui and Hawaii, sustaining forest bird populations.

High elevation areas have served as “refugia” on Kauai, Maui and Hawaii, sustaining forest bird populations. Ten years ago, you could practically count on one hand the number of native birds infected with malaria at 1900m on the island of Hawaii. Nowadays you couldn’t, unless you had more than double the amount of fingers.

And when it comes to funding and planning, there isn’t enough, both in Hawaii and the rest of the world, despite our general awareness of the potentially devastating effects of malaria on susceptible species. Atkinson says that when it comes to general funding for conservation of endangered forest birds, that it “needs to be increased by orders of magnitude if we are to avert a biological disaster in our lifetimes”.

Nobody denies that recent global efforts have made enormous progress in saving human lives, or that today’s avian extinction rate far exceeds that of just two decades ago.  Yet, the issues that face birds globally are largely being ignored, says George Fenwick, president of the American Bird Conservancy. And that’s not a good sign.  After all, most studies seem to show that malaria has been largely responsible for the recent wave of extinctions and endangerment among Hawaiian forest birds.

Many native Hawaiian birds that are considered “endangered” have already proven to be highly susceptible to disease in the wild. Nowadays, if you want to see a live honeycreeper you have to go to the tops of mountains, no less than 1500m (4920ft). There are exceptions – like the Hawaii Amakihi Hemignathus virens that still remains widely dispersed – but usually the birds only persist where temperatures prevent effective malaria development in mosquitoes. But at high altitudes, Atkinson maintains that it is quite likely that threatened bird species will be “squeezed between expanding disease transmission from lower elevations and the upper limits of suitable forest habitat“ due to a predicted rise in global temperature over the next  century.

kaui-flights_1

Many native bird species on islands, such as Kauai, are highly impacted by avian malaria. Over time, avian malaria has forced most of these species to breed in high elevation refugia where food and cover may be scarce. Refugia or “safe havens” are areas where natural environmental conditions have remained relatively constant or stable during times of great environmental change.

Alas, as tempting as it may be to write a comprehensive list on climate change and the altitudinal range of avian malaria in the Hawaiian Islands, this was not meant to be one. Plenty of those exist though. So for now, aside from what information is here, your best bet might be to check this 2014 publication out for more detailed information or look at this USGS update for some interesting facts and figures!

Further references

Atkinson, C.T. et al. (2000). Pathogenicity of Avian Malaria in Experimentally-infected Hawaii Amakihi. Journal of Wildlife Diseases, 36 (2), 197-204.

Beadell, J.S. et al. (2006). Global phylogeographic limits of Hawaii’s avian malaria. Proc. R. Soc. B., 273:2935-2944.

Freed, L.A. et al. (2005). Increase in Avian Malaria at Upper Elevation in Hawai’i. The Condor, 107: 753-764.

Kilpatrick, A.M. (2006). Facilitating the evolution of resistance to avian malaria in Hawaiian birds. Biological Conservation, 128:475-485.

LaPointe, D.A. et al. (2012). Ecology and Conservation Biology of Avian Malaria. Ann. N.Y. Acad. Sci., 1249: 211-226.

Louiseau, C. et al. (2007). Predictions of avian Plasmodium expansion under climate change. Scientific reports, 2: 1126.

Ricklefs, R.E. et al. (2004). Evolutionary Relationships, Cospeciation, and Host Switching in Avian Malaria Parasites. Syst. Biol., 53(1):111-119.

Samuel, M.D. et al. (2011). The dynamics, transmission, and population impacts of avian malaria in native Hawaiian birds: a modeling approach. Ecological applications, 21 (8), 2969-2973.

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