The lesson from the red kite: not all of us are resilient

Not all species adapt to extreme events such as drought, fires or other adverse climatic phenomena, whether temporary, such as a hurricane, or long-term, such as global warming.

The hackneyed resilience, the ability of a living being to adapt to a disturbing agent or an adverse state or situation, is a privilege of a few.

A study led by the Doñana Biological Station (EBD) – CSIC and

shows that a drought suffered by red kites at birth and during their first months of development causes lifelong damage, causing a decrease in their survival with serious effects on the population and precipitating, if urgent action is not taken, the remaining time for the extinction of the species in the National Park.

The scientific literature has analyzed dozens of animals and plants that migrate to habitats more conducive to climate change or that undergo modifications to survive the new conditions.

However, the research in which Julio Blas, a scientist at the Doñana Biological Station, has participated, shows that this is not the case for all species.

Taking the red kite (

) as an example and based on data obtained over three decades on the population that inhabits the Doñana National Park, the work shows that birds born during a drought carry the damage throughout their lives.

The monitoring of the kites has made it possible to determine that the stress associated with droughts during the birth stage generates a lack of nutritional resources and reduces life expectancy.

These effects on the individual have consequences on the entire population of Doñana, where the last 21 couples in critical danger of extinction take refuge.

If the causes of juvenile mortality are not remedied —demographic models predict extinction in the short term— and considering that part of the individuals were born in previous droughts, the forecasts for population decline are shortened, with a 40% decrease in sizes predicted population declines and a 21% shortening of the time to extinction.

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Doñana dries up completely

“We have analyzed what effect an extreme climatic event has, which in our case were the years of drought in Doñana, on the survival capacity, reproduction and behavior of a very specific species.

We wanted to see the effect of the current drought and we also wanted to look at the effect of the drought that may have existed at the time the specimens hatched.

We have been registering the population for 30 years and we have accumulated information for 700 individuals and data on 1,200 reproductive events”, explains Blas.

The research model can be used to analyze other species.

The study notes that “individuals born into poor quality habitats, stressful environments, or years of low food availability show impaired survival and reproduction in adult life in fish, reptiles, birds, and mammals, including humans.”

Previous research with other species has shown that adverse developmental conditions affect "individual morphology, metabolism, immunocompetence, physiology, sociability, and personality, with lifelong repercussions."

Blas is cautious in this regard: “We do not doubt that these effects can be generalized to other species.

But, as in any scientific investigation, we must be careful with the extrapolation of the result.

We have focused on the red kite because we have detailed information for 30 years and we could incorporate the drought parameter retrospectively.

However, it is very likely that these conclusions also occur in many other living beings”.

An event of extreme stress affects a population through two simultaneous pathways: it reduces the fitness of the adult individuals who cope with it and it impairs the development of those born during the same event.

In this way, the joint effects are devastating both in grown specimens and particularly in newborns, who remain damaged for the rest of their lives, whether or not they encounter new stress events.

In them, the effect known as “developmental restriction” occurs, whereby an adverse circumstance limits the quality of the phenotype and its future aptitude: “The phenotypes born in favorable environments are always superior to those generated under difficulties, regardless of the environment experienced. later in life."

Therefore, individuals raised in a benign environment, with little stress, are stronger and generate more prepared populations, while the difficulties faced in early stages of life generate individuals with a highly compromised future performance capacity.

Aerial view of the permanent lagoon of Santa Olalla, in Doñana, completely dried up on September 3.

DOÑANA BIOLOGICAL STATION (CSIC)

To reach these conclusions, the team of researchers has examined the demographic response in Doñana of the red kite, which under normal conditions can live up to 30 years.

When this population faces a year of drought, it must face a hostile environment, which implies a decrease (4.5 times less) in available prey: "a nutritional bottleneck" that limits the food available for the chicks and their parents, who In addition, they must make greater efforts to hunt.

The immediate consequence is a decrease in the number of offspring (between 46% and 37%) and a 330% reduction in their body condition, although not in their size.

For adults, droughts reduce their survival by 17%.

“The prey that adults bring to the nest decreases 1.7 times and they are not able to provide the nutrition that a chick requires during a normal year.

In addition, the effort they make to get that food is much greater than in a good year, so adults really wear themselves out”, explains the biologist.

"Our research shows that many of the predictive models used up to now to forecast the evolution of wildlife populations in the face of global change can be falsely optimistic," says the EBD researcher.

“Traditionally, the relationship between an environmental parameter, such as temperature or water availability, and one of biological efficiency, such as survival or reproduction, is studied.

Based on weather forecasts, some predictions are made, but most of these studies do not consider that there is an additional effect: how were the conditions at the time of the individual's birth.

If it is a threatened or endangered species, as is the case of the red kite, we realize that we do not have much time,

In this sense, Julio Blas issues an alert: “The Doñana red kite population is currently in a critical state in terms of population health.

In the last 30 years, the population has disappeared from practically all of Andalusia and even from most of Doñana, being restricted to the heart of the National Park.

There is a serious conservation problem and this year there are only 21 pairs left, compared to 80 30 years ago.

We must do everything in our power to prevent this mortality from occurring and, particularly, youth mortality.

There is currently a close collaboration with the National Park Conservation Group, which carries out important work with the available tools, for example, supplementing breeding pairs with food.

More action is needed

and this happens because those responsible for the conservation of the natural environment and those responsible for science agree and contribute more resources, and much more quickly.

If we don't do this, very soon we will stop seeing red kites in Doñana, forever losing a population adapted to a unique natural environment."

More and more intense droughts

The EDB study is especially relevant because episodes of lack of water will be more frequent and longer due to the increase in global temperatures.

"Droughts pose significant risks to people and ecosystems around the world," according to Rachel Warren, author of recent research from the University of East Anglia (UEA).

“Not only do the areas exposed to droughts increase with global warming, but also the duration of these increases.

Compliance with the Paris Agreements could reduce the risk of severe drought around the world.

This requires urgent action on a global scale now to stop deforestation and decarbonize the energy system,” she states.

Michael Bahn, a researcher at the Department of Ecology at the University of Innsbruck, agrees: "With ongoing climate change, extreme weather events will occur more frequently and dry periods will become more intense."

Bahn, author of several studies on the effects of drought on ecosystems, warns that, “as climate change progresses, mechanisms operating in global drylands could play an increasingly important role in many of the regions currently wetter.

However, their studies have found adaptations to adverse events in soil microorganisms.

In this sense, Bahn states: “Our recent article in

highlights that drought can leave legacies on ecosystems that change how they respond to subsequent similar events.

For example, in a long-term drought experiment it was observed that recurrent lack of water altered the composition of the soil microbial community and, unexpectedly, made the soil less susceptible to drought."

In the same sense, in two other investigations, he defends that the succession of times of scarcity of water resources alters the ecological memory of the soil and improves the resilience of ecosystems in the face of future episodes.

"The changes they bring about in soil communities [bacteria and fungi] can change how biodiversity buffers the effects of drought," he says.

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