The effect of climate change on bird life

Researchers Find That Mountain Birds Climb With Increasing Temperatures

Recent research has found that as tropical temperatures climb as a result of climate change, mountain-dwelling tropical birds are doing the same.

Cornell Sun

5 March, 2014

While climate change is not a new concept, the study conducted in Papua New Guinea aimed to examine the virtually unexplored question of climate change’s effects on birds, according to Benjamin Freeman grad and Alexandra Class Freeman, a staff researcher at the Cornell Lab of Ornithology.

“Climate change has a big impact on today’s world and there’s a problem in that nobody had really measured how climate change is impacting tropical birds,” Freeman said. “In our studies, we read about field work that Jared Diamond had done in the 1960s, and we realized that would give us an opportunity to go back to the same places, observe where birds live now and compare that to the historical baselines.”

Using 47 years of data previous research created a launching pad for a local study with wide applications, according to Class Freeman.

“In the present, these [data] are valuable. [We] got permission to work on this mountain to study climate change effects in the tropics to see whether diversity has changed,” Class Freeman said. “This ties a globally ambiguous symptom of greenhouse gas use to a real-world effects evident in bird species ranges on a spectacularly isolated mountaintop.”

After months of collecting data, the researchers found strong support for the existence of this trend of the birds’ ascent. Birds have shifted both the upper and lower elevation boundaries of their preferred habitats, Freeman said.

The impending effects of this trend could be lethal for birds, according to Class Freeman, who said it can only continue for so long before the population exceeds carrying capacity. Carrying capacity is the maximum number of members of a species that a habitat can support.

“Bird species living at the top are stuck, with no place to go, leading to their probable extinction if climate trends continue similarly,” Class Freeman said. 

“Mountains are cone-shaped, thus populations are much denser at the top — there is a sharing of smaller space by all species that inhabit mountaintops currently and those moving upslope. … This demonstrates that slight changes in climate can cause large changes in behavior.”

The particular lifestyle needs of these tropical birds make for an even grimmer picture when faced with relocation, according to Freeman.

“These are very different from our Ithaca birds that happily fly from Ithaca College to Cornell,” Freeman said. “These are birds that are born in a small patch of woods. … If they’re lucky enough to survive, they stay in one patch their whole lives.”

Due to the nature of interactions between species in an ecosystem, the effects of climate change are felt by all species in direct and indirect ways.

“The birds that eat insects that live in the understory tend to be born somewhere and live nearby their whole life,” Freeman said. “It’s a little warmer, so it probably changes the insects that live there … which may affect the birds.”

According to Freeman, this trickle-down effect of global climate change spells disaster for an increasing population of birds in a decreasing area of suitable habitat.

“A couple species that we studied that live on the mountaintop and are likely to go locally extinct are [the] Crested Berrypecker and Crested Satinbird,” Freeman said. “Even if a species persists … there’s less land area, and smaller populations will be supported for each species. … We think mountain extinctions are going to happen.”

The researchers themselves said they were surprised at the extent of the trend.

“We didn’t know really what to expect,” Freeman said. “It was surprising to me that so many species were moving up slope so strongly.”

Class Freeman said the uniformity of the trend at a variety of elevations was especially surprising.

“Lower elevation birds were moving up at about the same rate as upper, [which is] surprising mainly because you might expect some species to just expand if they could tolerate all temperatures — which we suspect they can,” Class Freeman said. “Species might be engaged in complex competition for habitat and food as they are squeezed into a smaller area at the top of a mountain.”

This complex interaction between species does not exclude humans, and according to Freeman tropical birds are not the only ones feeling the effects.

“People there already know they can grow coconuts up the mountain where their grandparents could not … they see it as a good thing … but also people are getting malaria in places where they weren’t before,” Freeman said.

Like the birds, humans can only advance so far up the mountain before reaching the top, and the end of new land to use.

“In Papua New Guinea, the concept of land ownership as we know it here doesn’t exist,” Class Freeman said.

“When you inherit your family’s given tract of land, if at some point you can’t grow anything on it due to climate change effects, you’ll be in a difficult place because you can’t just go up to the next plot — it’s not yours to take.”

Though the increase in temperature is small, according to Class Freeman, even a slight change could have large effects for both bird and man.

“Our research shows that the impacts are felt globally … even where there is only slight climate warming,” Class Freeman said.

Courtesy of Benjamin Freeman grad
Industrial impacts | Natural habitats and farm land in Papua New Guinea are feeling the effects of fossil fuel use in western industrialized nations, according to Benjamin Freeman grad and Alexandra Class Freeman, a researcher at the Lab of Ornithology.

With increasingly constricted amounts of land suitable for habitats desired by birds as well as crops desired by humans the livelihoods of both groups are threatened, according to Freeman.

“It’s climate change … some people benefit, just as the birds expand into new areas, [but] they contract into marginalized ones,” Freeman said. “Their whole livelihood is growing coffee, [and] that might disappear. … There’s winners and losers, [and] most of the mountain birds are losers.”

According to Freeman, the implications of the study were much wider in scope than its own temporal boundaries.

“Climate change tends to be invisible… maybe it’s [visible] in the arctic, but the changes are so minimal we don’t see it. You only see it if you look back to to a historical baseline [and] compare that to what is happening now,” Freeman said.

The study’s applications outspan the geographical boundaries as well, according to Class Freeman.

“Our study on the climate change demonstrates that the changes we feel in a tropical forest without infrastructure or anthropogenic change was largely caused by northern, industrialized countries,” Class Freeman said. “It was strong insight into the effects of fossil fuel use on remote tropical forests … Industrial countries, like the USA are doing this to the world and you can see the effects.”

Raising further questions about climate change’s effect on tropical birds and every step in between, the study has led the researchers to look to future possibilities for study in this field, according to Freeman.

“Understanding the ecological interactions that are important and somehow linked to the temperature increase — that would be an aspect for further study,” Freeman said.

Unfortunately, long-term studies on climate change effects are not easy to conduct, according to Class Freeman.

“[There are] a lot of different things that you’d have to tease out to get to the bottom of exactly why we are seeing species shift upslope,” Class Freeman said. 

“Sadly, there are very few places in the world where you can set up a 50-year research plan to systematically test hypotheses related to range shifts along an intact, protected, tropical mountain transect.”

According to Freeman, the researchers plan to take the challenge. “We’re going to do some research … in the way that species interactions such as competition might influence species responses to climate change,” Freeman said. “The same patterns are happening in the mountains here.”

Further studies could show whether or not the trend of ascent means doom or conquest for these high-aiming birds.

“[We call it an] escalator to extinction [that the birds are] going up until they run out of room. … If they’re the losers, the escalator is running quickly,” Freeman said. “Or, it’s king of the hill. … We don’t know which is the more correct scenario, [so] we’re going to do some experiments in the Adirondacks.”