Are You Finching Kidding Me?

The El Niño Booby Trap

Rhys Duarte

Sophomore College: Evolution and Conservation in Galápagos

Bill Durham

October 15, 2018

Figure 1: Two Nazca Boobies on Genovesa Island (Jonathan Hernandez) Figure 2: Female Medium Ground Finch on Santa Cruz Island

(Author)

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Abstract

El Niño is a significant weather phenomenon that has impacted many areas around the

world, one of the most notable being the Galapagos Islands. El Niño has been known to have

devastating effects on varying populations in these islands, such as seabirds, fish, and other

marine life. In this paper I will compare the effects of El Niño on two bird species found in

Galapagos, the Nazca booby (Sula granti) and the medium ground finch (Geospiza fortis). First,

I identified the main food supply of the boobies and finches, then analyzed how El Niño affects

the relative abundance of each of these food sources. In my research I found that El Niño has a

negative effect on sardines, the primary food source of Nazca boobies, thus harming the booby

population numbers. In contrast, the frequent rain from El Niño drives up the production of seeds

that ground finches feed on, thus proving beneficial to the population of the medium ground

finch. This project raises concerns about environmental issues such as the impact of climate

change on El Niño events, the potential danger of overfishing, and what can be done to help

preserve species that flourish under El Niño conditions.

Introduction

El Niño, or the warm phase of El Niño Southern Oscillation (ENSO), is a series of

irregular climatic changes induced by warm upwellings in ocean currents along the equator in the

Pacific region. El Niño typically brings water lacking in essential nutrients, which coupled with

the unusually warm temperature, can be harmful to marine life (Trenberth 1997). El Niño is

known to have a particularly strong presence in the Galapagos Islands given that the islands lie

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directly on the equator and are so far from the mainland. Their isolation prevents species from

easily escaping or migrating to other land when weather impacts their environment and available

resources, so El Niño has the potential to dramatically alter species’ food sources and

populations.

The first species I will be looking at in this paper with regards to their response to El

Niño is the Nazca booby (Sula granti). Nazca boobies are characterized by their orange beak and

black mask and have white feathers with a strip of black along the wing and tail. They are native

species of the Galapagos, meaning they arrived in the islands without human interference, but are

also found in other places such as the coast of Central and South America. Their diet primarily

consists of sardines, although they have been shown to eat flying fish, anchovies, and squid when

sardine supply is scarce (Wukitsch 2018).

I will be comparing the Nazca booby to another bird found in Galapagos, the medium

ground finch (Geospiza fortis). The finches in the Galapagos are often referred to as “Darwin’s

Finches”, and although Darwin did not do much work with the finches himself, they are still a

great example of evolution in real-time. There are

currently 14 species of finches on the islands,

although Darwin failed to realize that even the

slightest variation in beak or body size would

draw distinct lines between these species. The

medium ground finch is one of three species of

ground finches, with a body size around 12.5 cm

in length (Hau and Wikelski 2001). They are

endemic to Galapagos (found nowhere else in the Figure 1: The Galapagos Islands, home to the Nazca booby

and medium ground finch (Destination 360).

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world) and are found on ten of the islands. These finches primarily eat seeds, but have also been

known to eat buds, leaves, and occasionally insects. The medium ground finch prefers smaller,

softer seeds due to the size of its beak, but has adapted to eat larger, harder seeds after drought

conditions when seeds are scarce.

Nazca boobies and ground finches are particularly interesting to compare given the stark

contrast in their diet and response to ENSO events. By looking at the primary food source for

each species, researching the effect El Niño has on the availability of each source, then observing

the impact of food scarcity or surplus on these two species, I will be able to conclude the overall

impact of El Niño on medium ground finches and Nazca boobies. My hypotheses for the

response of each species to El Niño are as follows.

Hypotheses

1. Nazca boobies will have a depleted food supply during El Niño due to the effect on the

fish population, leading to a decrease in booby reproduction and survival.

2. El Niño will increase the food supply for medium ground finches, thus driving up

reproduction and success.

Methods

For the bulk of my research on the finches I will be citing a case study on medium ground

finches by Peter and Rosemary Grant in 2000. Thanks to the isolation of the Galapagos islands

and difficulty of migration for the birds from island to island, the Grants were able to closely

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monitor the behavior and breeding success of a specific population of finches on Daphne Minor.

The Grants have devoted much of their careers to researching these birds and have collected

extensive data, making their work the primary source of my research.

I will also draw from a study by Tompkins et al in 2017 that gathered data on the

abundance of boobies’ food supply and the corresponding effect on reproductive success. I will

additionally look at findings from Champagnon et al in 2018 that show the survival rate of

boobies during various El Niño productivity times. Unfortunately, the Nazca boobies have not

been monitored as closely as the finches but looking at the general trends in population dynamics

and food supply will give me a broad enough scope of the issue to draw conclusions for my

research.

Research Findings

Hypothesis 1

My first hypothesis is that El Niño will negatively affect the Nazca booby population due

to the decrease in sardines during El Niño years. To begin with, I will examine what the Nazca

boobies eat and why. Nazca boobies’ diet primarily consists of sardines, which are packed with

high-energy protein that provides them with an efficient form of nutrition. Compared to their

other food sources, sardines have the highest energy density and are generally readily available

for fishing, making them the preferred source of food for the boobies (Tompkins et al 2017).

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Since El Niño brings unusually warm sea surface temperatures and abnormal water

quality due to the high amounts of rainfall, this provides a harsh climate for the sardines. A study

by Barber and Chavez in 1983

analyzed the sea surface

temperature, rainfall anomaly, and

sardine catch during El Niño,

comparing the data in Figure 4.

From these results, we see that in the

months when the sea surface

temperature and amount of rainfall

spikes, indicating strong ENSO

conditions, there is a completely

opposite trend in sardine catch. In

April of 1983, after one of the most

well-known El Niño’s in Galapagos,

the SST and rainfall was so intense

that there were no sardines caught in

the study’s designated zone (Barber

and Chavez 1983).

Now that it has been established that El Niño does in fact limit, or completely remove,

the primary food supply for Nazca boobies, I will now look at the breeding success of Nazca

boobies depending on the availability of food. A study by Tompkins et al in 2017 compared the

type of food the Nazca boobies were eating with the probability of reproductive success. In order

Figure 2: This graph compares the average sea surface temperature, rainfall anomaly,

and sardine catch during specific months of El Niño years (Barber and Chavez 1983).

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to do this, they analyzed two “phases”: the sardine phase, or years that sardines were most

abundant and readily available for the boobies, and the flying fish phase, where sardines were

scarce and Nazca boobies had to turn to flying fish for sustenance. In this study, they found that

in the years where sardines were plentiful, the Nazca boobies had an almost 40% higher

probability of reproductive success than in years where sardines were not available (Tompkins et

al 2017).

Figure 3: This graph compares the probability of reproductive success with the type of food Nazca boobies are primarily eating,

either sardines or flying fish (adapted from Tompkins et al 2017).

This decline in success during the flying fish phase can be attributed to two factors. First,

during this phase the boobies experienced a lower energy density in their diet. This means that

flying fish and other sources of food were not as protein-rich as the sardines, and the boobies

were not as efficient in fueling themselves (Tompkins et al 2017). Additionally, they had lower

foraging success overall, which could be attributed to the unfamiliarity of their new diet and

difficulty finding sardines.

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Overall, this low-energy diet had an extremely negative effect on the booby population. Not

only did they have lower reproductive success, but the study also determined that on the flying

fish diet, the time between the Nazca boobies’ offspring’s hatching and acquisition of plumage

was eight days longer compared to the sardine diet. This could be detrimental to the species

because if the boobies are taking longer to mature, they remain dependent on their parents and

are vulnerable to predators or environmental factors that could harm these young birds. Going

back to my original hypothesis (Nazca boobies will have a depleted food supply during El Niño

due to the effect on the fish population, leading to a decrease in booby reproduction and

survival), I argue that this is supported by my research. The lack of sardines led to an overall

decrease in the fitness of Nazca boobies by providing them with a less energy-rich diet, hurt their

reproductive success, and left boobies weaker and more vulnerable. Figure 6 shows that as El

Niño’s grow stronger, there is in fact a decline in the Nazca booby survival probability.

Figure 4: This graph compares the strength of the El Niño with the annual survival

probability of Nazca boobies (Champagnon et al 2018).

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Hypothesis 2

The second hypothesis I aim to test in my research is that El Niño will increase the food

supply for medium ground finches, driving up reproduction and success. As with the Nazca

boobies, I first looked at the primary food source of the finches. Medium ground finches mostly

eat seeds, although as mentioned earlier, occasionally flowers, buds, leaves, and insects (Trevor

1987). I will be focusing on seeds specifically since they are the main food source for finches. In

Galapagos there are varying sizes of seeds, ranging from very small and soft to large and

difficult to crack. The medium

ground finch has adapted to be able

to crack some of the larger seeds,

although this is not always the most

efficient option for them. Since

cracking large seeds can be very

difficult for birds with small or

medium sized beaks, finches may

spend more energy trying to open

the seed than they are rewarded with

for eating the seed. Thus, while the

large seeds provide more fuel for the finches, it is beneficial to have a variety of seeds, allowing

the medium finches to eat the small ones as well. During El Niño years, the increased amount of

rainfall provides fertile soil for rich seed growth (inferred from a study on soil productivity due

to El Niño in India, Bhuvaneswari et al 2013), allowing there to be an abundant variety of seeds.

Figure 5: This image shows different types of seeds that finches eat with a size comparison to

large beaked finches and small beaked finches, adapted from Trevor 1987.

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If there is no struggle to find food and they have many types of seeds available to them, the

finches should have no competition among themselves and be able to reproduce freely.

Thanks to the close monitoring of the finches by Peter and Rosemary Grant, the effect of this

surplus is evident by comparing medium finch productivity and success during El Niño and non-

El Niño years. The charts below give this data from one of their studies in 2000.

From the data on medium finch productivity Figure 9, we see that, on average, females

were producing significantly more eggs per year during ENSO conditions. This could be

attributed to the overall health of females given the availability of food, or a higher frequency of

reproduction during the year since there is no competition or struggle for survival. Figure 8

shows the success of hatchlings and fledglings of medium ground finches in El Niño vs. non-El

Niño years. Again, we see that during El Niño years, the finches were slightly more successful.

Figure 6: This table compares medium ground finches' hatching success and fledging success in El Niño vs. non- El Niño years (Grant et al 2000).

Figure 7: This table compares the annual production of eggs per female and fledglings per female in El Niño vs. non-El Niño years (Grant et al

2000).

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Not only was there a higher rate of eggs hatching and becoming nestlings, but there was a higher

chance of nestlings maturing and becoming fledglings.

The effects of El Niño are again apparent on these finches, but this time in an opposite

way than the Nazca boobies. Given the data collected by Grants and other scientists, I conclude

that my second hypothesis (El Niño will increase the food supply for medium ground finches,

thus driving up reproduction and success) is supported. If El Niño fosters a large supply of seeds,

and the ground finches have the most reproductive success during these years, it is reasonable to

assume that their success can be attributed to the lack of food competition and security of

resources.

Conclusion

Overall, it is clear that the impact of El Niño is strong in medium ground finch and Nazca

booby populations. On one hand, the main source of food for Nazca boobies, sardines, was not

able to withstand the harsh weather conditions brought on by ENSO events. This caused a

decrease in the sardine population, in turn negatively affecting the reproductive success of Nazca

boobies. Alternatively, the heavy rainfall brought on a productive season for medium ground

finches, driving up the seed supply and allowing the finches to reproduce more frequently with

more success. Often, El Niño is portrayed as devastating to most life forms in the Galapagos due

to the spike in sea surface temperature and rainfall which harms production of key nutrients and

alters conditions for marine life. I wanted to highlight the fact that El Niño impacts species in

very different and sometimes opposite ways, however it still results in an ecosystem out of

balance, which is often unstable. Highlighting the differences in how species react to an extreme

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environmental change can help us understand factors contributing to overall survival and success

in a species, which is crucial to implementing conservation efforts and protecting species.

Conservation Implications

While neither of these two species are

threatened or listen under immediate danger by the

International Union for Conservation of Nature

(IUCN), it is still extremely important to consider the

effects of our actions on the environment. We should

take particular care to protect species whose numbers

are not threatened because it is not too late to preserve them, and we have control over our future

actions that dictate their outcomes. First of all, if climate change is bringing more frequent El

Niño’s, we are called to take action to combat climate change by cutting back on CO2 emissions,

reducing waste, and educating ourselves about our environmental footprint. Additionally, after

seeing the effect of the depleted sardine population on the Nazca boobies, regulating overfishing

in not only the Galapagos but other environments is crucial to preserving the food chain and

maintaining a balanced ecosystem. The finches are an interesting case. If El Niño is so harmful

to so many Galapagos species but causes the finches to thrive, what can we do to make sure the

finches survive in a way that is sustainable to other species? We as humans need to constantly

think of new, relevant ways to protect species so future generations can visit places like

Figure 8: A sign outside the airport in Baltra asking

tourists not to feed the finches (Author).

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Galapagos with a minimum impact and people can continue to learn about Darwin’s legacy and

why native Galapagos species are so important.

Acknowledgements

I would like to thank Bill Durham, Caroline Ferguson, Neil Nathan, and all the wonderful

Sophomore College students for making this such an incredible and eye-opening experience!

Figure 9: A male ground finch perches on a countertop in Puerto Ayora (Author).

Figure 10: A view of the beautiful, crystal blue water of Galapagos Islands, with the incredible La Pinta in the

background (Author).

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