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An ornithologist and an entomologist go into the kīpuka…

There is something magical about reading a well-written, remarkable paper from outside of your sub-discipline — the echoes of familiarity in methodology, the unpredictable overlaps, the serendipity of finding the research in the first place. I recently found this magic in Vertical foraging shifts in Hawaiian forest birds in response to invasive rat removal, published in PLoS ONE in September 2018. Co-first-authors Dr. Erin E. Wilson Rankin and Dr. Jessie L. Knowlton transported me to the northeast slope of Mauna Loa Volcano for a bird-watching and bug-counting adventure through a network of half rat-eradicated kīpuka — a jigsaw puzzle of fragmented forest pieces dissected by lava flows.


By most measures, I should never have read this paper. It came out while I was staggering though the first weeks of parental leave last fall. My invasive species are plants (not rats); there’s really no vertical space available (the trees are too short!) for shifts in arthropods or their predators in my plant communities at treeline; my island study site (downeast Maine) hasn’t seen volcanic activity for hundreds of millions of years (Hawaii’s kīpuka are created when volcanic lava flows move through native forests). For reasons I can’t explain, earlier this month I clicked on a link to The Wildlife Society’s — a society I’m not a part of and don’t actually follow on social media — Wildlife Publication Awards 2019 shortlist announcement. At the end of the Journal Paper category, this Hawaii study caught my eye, because I’m planning a trip there in the fall and recently spent three early morning hours driving through Iowa and Minnesota with my friend who is a postdoc at the University of Hawaii, Hilo. Despite the winding the path to get this paper into my To Read Folder, there was a straight line from my final scroll through the Conclusions to the “compose” button on my email. I had to hear more from Drs. Wilson Rankin and Knowlton.

Photos by Erin Wilson Rankin. Top a happy face spiders taken under a scope and nocturnal spider in the kipuka. bottom: a sticky trap for sampling arthropods, a native bee on the ohia flower.

Here is what my initial google searches turned up: stunning photographs of kīpuka; and the discovery that the two first authors, now faculty at UC Riverside and Wheaton College, were postdocs on this project who first came to the kīpuka from the subfields of entomology (Dr. Wilson Rankin) and ornithology (Dr. Knowlton) back in 2011. The invasive rat removal efforts in their paper was a part of a larger study: 16 kīpuka fragments were methodically outfitted with trapping grids and compared to another 18 kīpuka without rat traps. “The larger study has examined how impacts by invasive predators (rats) change across a gradient of ecosystem size,” Wilson Rankin and Knowlton explained to me. “The kīpuka are a patchwork of forest fragments that were created when volcanic lava flows moved through native forests. The result is a landscape dotted with naturally fragmented forest patches that range in size from very small (<0.1 ha) to very large (>12 ha). This study system allowed us to tease apart the effects of invasive rats and the effects of ecosystem (or forest patch size) in order to better understand the forces that shape communities.”


I asked how an entomologist and an ornithologist from different universities on the US mainland ended up working together in Hawaii. “The kīpuka project was a highly collaborative project among PIs at Stanford University, University of Maryland, Michigan Tech, and the US Forest Service that integrated multiple research fields to examine the effects of an invader on native communities.” They confirmed what google had hinted about their origin story. “We both joined this project early on as post-docs, one focusing on quantifying invasion impacts on the arthropod communities and the other focusing on the responses of native forest birds. By bringing together a research team with diverse backgrounds and expertise, the kīpuka project was able to develop a broad and in-depth understanding of how rats shape the invaded communities and alter the interactions among native species.” They ultimately found that the presence of invasive rats altered the foraging behavior of native birds — in rat-filled fragments the birds foraged higher in the canopy. The rats are not found above 6 m in the forest, but they seem to control the arthropod biomass below 6 m, suppressing the resources available for birds, especially insectivores and frugivores. In sites without rats, there was more arthropod biomass below 6 m and birds foraged at lower mean heights compared to higher foraging heights in control kīpuka.

birds of kīpuka fieldwork photos by Jessie Knowlton

These kīpuka are like the matryoshka dolls of island biogeography, a model system in a model system. The forest fragments are islands of habitat, and these in turn are contained within the island of Hawai‘i. I asked Wilson Rankin and Knowlton what they hoped managers in other systems could learn from this work. They write, “The fact that the kīpuka are fragments of habitat within a less hospitable matrix makes them comparable to other fragmented systems, which, as we all know, are increasingly common as human development continues to expand through natural habitats.” The kīpuka islands within islands system is special, but can still contribute to our understanding about invasive species in general. “While Hawaii is unique because of its high number of endemic species and long isolation from mammalian predators, many fragmented habitats are having to contend with extinctions of native species and invasions of nonnative species, even on the mainland. Our work shows that these invaders can alter whole trophic systems, either directly or via shifts in species’ behavior. This work helps to highlight the importance of considering the synergistic and sometimes unpredictable effects that habitat fragmentation and invasive species together can have on native food webs. We hope that both factors will be taken into account when planning restoration or conservation actions.”


Finally, I just loved the opportunity to write about two women in STEM and their postdoc work. And I told Wilson Rankin and Knowlton that I appreciated reading a new paper covering fieldwork that concluded six years ago. My own dissertation research from 2011-2013 is just reaching publication now too. As they write, “Patience and persistence are the two key words when it comes to getting your research published.” Wilson Rankin and Knowlton shared this reflection on the triumphs and low points of the journey from fieldwork to award-winning publication: “We both came onto this project as postdocs, and supervised the data collection for the three years of field research. After that we both went on to other positions, and thus had to balance writing up manuscripts from this research with the demands of new positions. Once submitted, this manuscript went through the revision process, which took some time but we are all pleased with the end product. In general, our advice to others would be to not be discouraged during the review process or its pace, as you can always improve a manuscript and the reviews are meant to help you improve your work.” Somehow, this magical paper also brought some timely advice into my email inbox as I head into a summer of writing up first drafts of my own postdoc papers. I welcome this nice reminder to keep grinding, and to keep working with some of my fabulous peer-collaborators as they embark on new adventures and new jobs in the coming years. And of course, I am now more excited than ever to spend some time in Hawaii with conservation researchers this fall!


Wilson Rankin EE, Knowlton JL, Gruner DS, Flaspohler DJ, Giardina CP, Leopold DR, et al. (2018) Vertical foraging shifts in Hawaiian forest birds in response to invasive rat removal. PLoS ONE 13(9): e0202869.


Banner image: photo by Jessie Knowlton.

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