Researchers from the Doñana Biological Station – CSIC have examined the effect of natal and current drought on the survival and reproductive rates and behaviour of the Red kite population of Doñana National Park. The aim was to analyse the impact of current climate extremes and also the ones experienced in the past by animal populations.
"We urgently needed to know the answers to some questions. What is the combined impact of natal and current extremes? Is extreme climate more deleterious when encountered as an adult or when experienced at birth? Does a natal extreme undermine the capability of an adult to cope with another extreme encountered later on in life?", explained Fabrizio Sergio, researcher at Doñana Biological Station and lead author. According to the researcher, these are important questions to answer, considering that extreme events and their outcome hardship will become more and more frequent in the near future, increasing the probability that individuals will experience them both at birth and again as adults.
The study was performed using a sample of 700 individuals, long-term monitored over three decades (between the years 1989 and 2019), and around 1200 breeding attemps. In Doñana, Red kites are endangered (there are barely 20 pairs currently) and depend for food on a large seasonal wetland, the "marisma". In years of drought, the marisma never floods and remains basically dry, converting the whole ecosystem in an arid steppe with scarce food for kites.
Worse breeding success and lower survival rate
"We found that drought depressed red kite breeding success and survival", says Julio Blas, researcher at Doñana Biological Station – CSIC and co-author. "When drought occurred in the year of birth, it lowered the survival probability of an average individual for the rest of its life". For example, an individual born during a normal year had an average life expectancy of 10 years, while a kite born during a drought had a life expectancy of little more than one year, insufficient to generate any progeny".
The team also worked on a modelling of population dynamics, which showed that ignoring natal hardship may create a very optimistic and biased forecast of future population size and trend. This would prevent the necessary awareness of the seriousness of the situation of threatened species, which could jeopardize application of conservation measures with the necessary urgency. For example, for red kites, incorporating natal drought into the picture caused a 40% decline in forecasted population size and a 21% shortening of time to extinction. According to Julio Blas, the modelling shows that the expected future increases in drought frequency "will steepen the already ongoing population decline and shorten its time to extinction, making management of this population even more urgent".
Assessments and forecasts of climate impacts are usually base on linking demographic measures of performance (such as reproductive success, survival rates) to the climate conditions occurring during such performance. For example, the breeding success is typically related to the mean temperature recorded during breeding. "However, according to our findings, this type of traditionally simplistic analysis needs to take more into account the potential contribution of natal effects, as this may radically worsen the predicted scenarios for the future", explains the researcher.
Global change, more severe than expected
Because natal shocks/hardship may impair individuals through their whole life and affect their performance even decades later, their effect can be subtle and difficult to detect. This is because, according to the researchers, they hit a population twice, by directly affecting adults and by injecting into the population a pool of weak individuals impaired for life. This could contribute to explain the mysterious large-scale declines observed in many animal groups worldwide.
In addition, synergies between natal and current conditions may apply to any type of anthropogenic impact provoking stress and hardship for both offspring and adults, such as chemical contamination or human disturbance. Fabrizio Sergio says "the implication of all this is that climate and global change may be eroding populations more quickly and severely than generally recognized". This will require, according to the researcher, more urgent and intensive conservation measures. "As for many aspects of climate change, we may be running out of time faster than commonly understood".
In the future, it will be important to conduct similar studies on other species in order to confirm the generality of these findings. In the meanwhile, there is an urgent need to incorporate "penalties" for natal effects into forecasts of climate impacts as conservative, worst-case scenarios.
"In the specific case of Red kites in Doñana, the forecasted future increase in drought frequency and intensity due to climate change and the illegal water extraction for agriculture will accelerate the disappearance of this predator, currently endangered. That's why urgent conservation measures are needed", affirms Julio Blas. As a measure, programs of supplementary feeding, already enacted by the Conservation Group of the National Park, could be intensified during drought to try to increase the quality and future performance of young kites born under these difficult conditions. "Adopting this and other measures requires environmental conservation managers and researchers agree to urgently add adequate resources. Current funding is insufficient. We need to invest more quickly if we don't want to fail in our attempt to keep the red kite alive in Doñana", concludes Julio Blas.
Sergio, F., Tavecchia, G., Blas, J., Tanferna, A., Hiraldo, F., Korpimaki, E & Beissinger, S.R. 2022. Hardship at birth alters the impact of climate change on a long-lived predator. Nature Communications. DOI: https://www.doi.org/10.1038/s41467-022-33011-7
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