Sacha Heath

Natural habitat increases bird abundance and reduces crop pests in areas with intensive agriculture

Contributed by Ash Zemenick @mtn_ash and Sacha Heath @SachaHeath


Agriculture, Agroecosystem, Animals, Community ecology, Conservation, Consumption, Ecology, Experimental, Field, Indirect, Interactions, LGBTQIA+, North America, Observational, Predator-Prey, Queer, Species richness, Terrestrial, Trophic cascade, Woman



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Sacha K. Heath and Rachel F. Long. 2019. Multiscale habitat mediates pest reduction by birds in an intensive agricultural region. Ecosphere 10(10):e02884. 10.1002/ecs2.2884 link


Sacha K. Heath, Candan U. Soykan, Karen L. Velas, Rodd Kelsey, and Sara M. Krossd. 2017.  A bustle in the hedgerow: Woody field margins boost on farm avian diversity and abundance in an intensive agricultural landscape. Biological Conservation 212: 153–161 link



Slide 1: Researcher’s Background

Sacha Heath is an ecologist who studies biodiversity and conservation, often with a focus on birds, and is an advocate for diversity and equity in STEM. She is currently a postdoctoral fellow at the Living Earth Collaborative.


PB: Why did you become a biologist?

SH: As an undergraduate, I started out interested in the relationship between humans and the environment and was deeply disturbed by the destruction of the natural world. At first I thought I would go into environmental policy or environmental education. But as I dove more into the issues, I became fascinated with the ecology, biology, and natural history of the organisms themselves: the plants, the birds, the mammals, the insects; and I also had a strong realization that I could not help protect something that I knew not much about. So I shifted gears and decided to become a research ecologist to study not only birds and insects and plants, but also the ways in which we try to conserve species and the environment. I wanted to provide scientific information to help the policy makers make decisions based on the best available science, and to the educators to teach the world about the creatures with which we share the planet.


PB: What is your favorite part about your job?

SH: In equal measure, I love field work (being outside, watching nature, taking data) and I love analysing data (doing statistics, finding creative ways to present the results).


PB: What obstacles have you overcome to get where you are?

SH: I feel lucky in so many ways. My family had the financial means to help me go to school without me having to worry about working at the same time or to go into debt. Even so, my greatest barriers were self-confidence, and despite funds – a lack of support to help me navigate important steps along the way. I often felt very alone and I think my response was to put on a front that I didn’t need any help – which just led to more loneliness. I was also sexually harassed by a few key mentors (before graduate school), which really contributed to my lack of self-confidence and loneliness, and resulted in me questioning whether I deserved my own accomplishments. Finally, as a queer woman who also wanted to do the kind of science that took me to remote places in field camps with only a handful of people, I was and am always uneased when navigating whether or not I am in a safe environment to be out as a queer woman. It was when I learned to ask for help and began talking about some of these things, that I found a supportive community, and I was able to stick with my passion and become who I wanted to be.


PB: What advice do you have for aspiring biologists?

SH: Don’t be afraid to ask questions! In my opinion, being creative and curious and open is the foundation of being a good scientist. This includes asking for help when you need it, and also trying to not be afraid of failure. Failure is a part of science: we often ask questions that go nowhere or make a mistake in an experiment, but almost always we learn something from it and the failure leads to something new and exciting. I think people that are under-represented or marginalized in STEM often feel the extra burden of needing to be perfect in order to represent their entire group – try to not add on this extra burden and instead center your curiosity about what it is you are passionate about.


PB: Do you feel that any dimension of your identity is invisible or under-represented/marginalized in STEM?

SH: My thoughts on this have progressed through time as our society has progressed – with a caveat. As an undergraduate student in the early 1990s, I frankly thought I was the only queer person in the world to love nature, the outdoors, and science! This of course was not true, and now I find that the queer community is everywhere, in every profession, and is much more visible. But this is a very regional thing, and though I am lucky to be in places where I can find other queer scientists and can be very open about who I am, I know that this is not the case for everyone, even in the U.S. and especially for people doing research in areas where it is literally illegal for queer people to exist. I feel that despite our new-found visibility and some important legal protections in the U.S. and other countries, what remains invisible are the ways in which being queer still greatly affects daily decisions that most can take for granted. For example, where one works and lives involves difficult decisions for everyone, but I also have to take into consideration things like whether the state in which I have a job has legal protections for LGBTQ people in our professional and residential spaces (in some states we can be fired or kicked out of our homes because we are queer and we have no legal protections). There are certain places in the world where my spouse does research where we must pretend that we are friends or co-workers. These types of things remain stressful and do come into play when making important life decisions. I think there is a lack of visibility in regards to those types of issues – even among my most supportive colleagues.


Slide 2: Research Overview

Take home message of study

Dr. Heath and her collaborator studied the effect of landscape context (the amount of semi-natural habitat in the landscape; cleared, simple, and complex) on bird community composition and predation of an important pest of walnuts: the codling moth (Cydia pomonella). They surveyed bird communities and performed a sentinel prey (codling moth larvae) exclosure experiment in walnut orchards in the Sacramento Valley, California, USA—comparing predation probability between orchards with (n = 10) and without (n = 10) local woody habitat at the uncultivated orchard edges, and between larvae that were caged (no bird access) and uncaged (birds had access) – First figure. They first found that the presence and increasing complexity of this local woody habitat increased the species richness and abundance of bird species that were likely or confirmed predators of the codling moth larvae. Second, the amount of predation by birds increased as the amount of semi-natural habitat in the wider landscape increased (bottom figure, next slide). Third, in cleared and simple landscapes (but not complex habitats) the greater abundance of woodpeckers was associated with higher predation of codling moth larvae (top figure). This highlights the importance of maintaining semi-natural cover around orchards in intensive agricultural regions because they can help control important pests.


Study system

The study was performed in walnut orchards in California’s Sacramento Valley. The caption from the paper reads: “Tan rectangles represent orchard margin transects with or without woody habitat patches. 300-m bird strip-transects denoted by gray dotted lines in margins and orchard interiors. Sentinel tree transects are tree symbols, with five caged (X) or uncaged sentinel cocoons.” Dr. Heath also measured the amount of semi-natural habitat in the larger landscape around each orchard.


Slide 3: Key Research Points

Main figure

The first plot (on top) shows the relationship of woodpecker abundance (x-axis) and the probability of predation of codling moth larvae (y-axis) in different landscape contexts: cleared landscapes (left panel), simple landscapes (middle panel), and complex landscapes (right panel). The data show that in cleared and simple landscapes, the probability of codling moth predation increases with the abundance of woodpeckers. However, in complex landscapes, there is no significant relationship between woodpecker abundance and the probability of codling moth predation.

But complex habitats were also really important for predation by birds! This can be seen in the plot on the bottom of the slide, where their data shows that the probability of predation of codling moth larvae (y-axis) increased with seminatural landscape cover (x-axis) on trees that did not exclude birds with cages (green). Sites that had the highest seminatural landscape cover (right side of the x-axis, bottom slide) were also the complex landscapes shown in the top figure (right panel). They hypothesized that adding more woodpeckers to the mix in these complex landscapes, that already had high predation and many woodpeckers, did not increase predation rates (top figure, right panel).

Societal Relevance

Humans have converted much of our terrestrial landscapes into agriculture, which has reduced habitat available for many non-human species. However, when managed with sustainability and conservation in mind, agricultural landscapes can serve as “nature’s matrix” and provide habitat to many species which can perform pest control services on our farms, and reduce our reliance on pesticides. One conservation management tool involves preserving natural habitat on crop margins, or restoring field margins to have native species. Evaluation of the biodiversity benefits of non-crop habitat has lagged behind implementation, however, especially in the United States where this habitat has the potential to supply important resources for both common and rare species of birds. Therefore, work like this is really important to understand how best to diversify farms to sustain biodiversity and while also making sure that crops are not being negatively affected by these practices.

One Comment

  • Bibit Traut

    Hi Sacha! I just came across while looking for materials for an online lecture. I am so happy to see how successful you are and that you are providing a great example to so many people.

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