CLIMATE CHANGE THREATENS BIRDS
THIS POST IS A CRITICAL REVIEW OF THE RESEARCH FINDING THAT GLOBAL WARMING SHRINKS BIRD BREEDING WINDOWS AND THUS THREATENS THEIR SURVIVAL [LINK]
PART-1: WHAT THE RESEARCH PAPER SAYS
- For breeding birds, timing is everything. Most species have just a narrow window to get the food they need to feed their brood—after spring’s bounty has sprung, but before other bird species swoop in to compete. Now, a new study suggests that as the climate warms, birds are not only breeding earlier, but their breeding windows are also shrinking by as long as 4 to 5 days. This could lead to increased competition for food that might threaten many bird populations.
- Birds typically time their breeding to cues signaling the start of spring, so that their chicks hatch when food like plants and insects is most abundant. But global warming has pushed many species to breed earlier in the year; that effect is especially prominent at higher latitudes, where temperatures are rising faster than near the equator. Few studies, however, have examined how climate change affects the duration of breeding windows, which closely track the number of chicks born each year as well as overall population trends.
- To find out how the length of breeding periods has changed over time, a team led by Maria Hällfors, an ecologist at the University of Helsinki, analyzed an extensive data set from amateur ornithologists coordinated by the Finnish Museum of Natural History. The data set spans from 1975 to 2017 and includes the nesting records of 73 species and more than 820,000 birds from a 1000-square-kilometer area in Finland’s boreal forests. Each year, trained volunteers placed uniquely numbered rings around the legs of newly hatched chicks to track their movements and survival. Because chicks had to be a certain size to get a ring, the researchers were able to use the timing of the tagging to work out when each chick had hatched—and therefore when breeding had occurred.
- On average, the beginnings and ends of the breeding periods are occurring earlier in the year. However, the ends are shifting back faster than the beginnings, resulting in an average breeding window that is 1.7 days shorter in 2017 than it was in 1975. During that same period, Finland’s average temperature rose by 0.8C, suggesting many bird species are actively responding to changing temperatures, Hällfors says.
- „It’s good for the species if it’s able to follow the optimum conditions as the climate changes,” she says. However, the shorter breeding windows mean more birds are breeding earlier in the season—a risky time for chicks’ survival, especially if the weather turns suddenly cold. In addition, because many late-season species are shifting their breeding windows up, that could mean more competition for food and nesting sites early on, leaving some chicks to go hungry. Although the researchers were unable to tease out overall population trends from their data set, Hällfors expects these shifts will have a large impact on bird numbers, with some species outcompeting others.
- Lucyna Halupka, an ecologist at the University of Wrocław, calls the study “a very important paper” because it’s one of the few to measure the breeding period duration. For 2 decades, she says, many scientists studying birds and climate change have looked only at the earliest, median, or mean laying dates for specific groups of birds. However, she cautions that because the study is limited to Finland, the findings may not apply universally; future studies should examine how breeding seasons move in other regions where the effect of climate change is different. They should also try to determine how shifting breeding windows affect population sizes, she says.
- For Hällfors, the new findings illustrate the power of long-term data sets. “Imagine the bird-ringing ornithologists in the 1970s,” she says. “They probably couldn’t have imagined that their data would be used in 2020 to look at climate change.” It’s also a valuable addition to other ongoing climate change research, says conservation biologist Stuart Butchart of BirdLife International. “Many people still think of climate change as a problem that’s going to arise in the future,” he says. “This is another study showing that entire communities of species have already shown substantial responses to climate change over recent decades.”
PART-2: CRITICAL COMMENTARY
- CLAIM: „average breeding window that is 1.7 days shorter in 2017 than it was in 1975. During that same period, Finland’s average temperature rose by 0.8C, suggesting many bird species are actively responding to changing temperatures“ RESPONSE: That the observed breeding window shortened over a 42-year period during which temperatures rose by 0.8C does not serve as evidence for causation. The timescale (whether annual or longer) for the response of breeding time to temperature must be specified from theoretical considerations. And then it must be shown with detrended correlation analysis that breeding time is responsive to rising temperature at that time scale. As presented these data imply a time scale of 42 years and a sample size of one. No statistically significant evidence for causation can be found in a sample size of N=1.0.
- Consider for example, that the following important changes occurred in Finland in the same time period over which a temperature rise of 0.8C was observed. In 1991 Finland’s economy went through a boom and bust cycle. In 1995 Finland joined the EU. In 2009, A tragic mall shooting event occurred. In 2011 Cyclone Dagmar struck Finland. In 2012 Hyvinkää shooting occurred. In 2013 Jyväskylä library stabbing occurred and Nordic storms struck Finland. Yet, no one would suggest, simply from theiir co-occurrence that these events were causally related to either the temperature or or the breeding habits of birds. By the same logic, that the breeding habits of birds shrank during a period of warming does imply either that shorter breeding habits caused warming or that warming caused shorter breeding habits.
- CLAIM: The impact of global warming on the breeding habits of birds can be assessed by observations of breeding habits in Finland and the observations of temperatures in Finland. RESPONSE: The impact of global warming on the breeding habits of birds cannot be established with data from a relatively small geographical region of the earth. Finland occupies about 0.227% of the world’s land area. As explained in a related post [LINK] , the impact of global warming is best understood in terms of global mean temperature or significant latitudinal sections thereof over sufficiently long time spans of more than 30 years. In this case, though the time span criterion is met, the extreme localization of the data to 0.227% of the world’s land area does not contain information that can be generalized in a global warming context.
- CONCLUSION: We conclude from the analysis above that the data presented as evidence for the causation of changes in observed breeding habits of birds by global warming contain significant weaknesses such that they do not serve as evidence that global warming has changed the breeding habits of birds. Firstly, the observation that events A and B occurred over the same time span does not serve as evidence of causation. And second, the extreme geographical localization of the data for both bird breeding habits and for temperature makes it impossible to interpret these events in the context of global warming.
— Thongchai Thailand