2018-10-19 14:12:23
As much as they say that the world belongs to the brave, in the face of real danger, putting land in the middle is usually a safer formula to preserve life. Being realistic, the world belongs to cowards, because, as my grandfather used to say, “cemeteries are full of brave men”. This is clear to many creatures in nature, especially birds, which, in addition to running in the face of danger, can take flight, which is much more effective when it comes to putting land in the way. Our interviewee, Mario Diaz Estebanresearcher in the Department of Biogeography and Global Change of the National Museum of Natural Sciences, CSIChas been able to verify these things, as has been reflected in a recently published article in Scientific Reports.
Mario Díaz, along with a large panel of scientists, has been studying the risk and escape strategies used by different migratory birds when a predator is around. The recently published study summarizes the behavior of 10,877 individuals of more than 20 species of migratory birds, which have been observed by scientists and ornithologists spread across different parts of Europe, the Near East and Africa.
Migratory birds travel long distances all over the planet and in each place they carry out different vital activities. At certain times of the year they live in northern lands, where resources are abundant, and there they mate and breed. When resources become scarce, they take flight and travel vast distances, stopping in between to feed and replenish their strength. Finally, they arrive at the wintering sites where they continue to feed and prepare for the return trip, when the weather conditions are optimal again in the breeding area. How do the birds behave at each of those moments if they detect the presence of a predator? Do they cautiously fly away or wait for the enemy to approach at a distance they consider safe before taking flight?
Researchers have observed the behavior of birds in different places and situations using a method that is as ingenious as it is simple. The method consists, as Mario Díaz comments during the interview, of “scaring birds away”. The researcher, acting as a predator, something that, knowing the human being, is not exaggerated at all, approaches the bird to study and notes the distance at which it flees from him. This safety distance, which the bird decides to put between itself and the researcher, is a measure of the risk it assumes.
The risks that the different species run, explains Mario Díaz, depend on the balance between the costs and benefits of fleeing. If a bird is feeding and a predator approaches, it must gauge when it is going to stop feeding and take flight, this entails costs and benefits. The main benefit is to avoid being captured by the predator and to preserve life, that is clear. However, if the bird is feeding, it knows that fleeing will force it to stop feeding and, in addition, it will have an additional cost of energy for fleeing. The need to feed is essential for its survival, especially at certain times in the bird’s life, for example, when it breeds, because it must feed its chicks. It is also important at other times. for example, when a stopover is made halfway during the migration, since feeding allows it to store the energy that it will expend during the rest of the journey. In these circumstances, any reduction in stocks may endanger his own existence or that of his offspring. Thus, the risk it runs by reducing the safety distance from the predator is significant. Scientists have verified that calculating risk, measured in the form of “flight distance”, makes it possible to evaluate vital behaviors of birds in different circumstances.
In the research that we are discussing today, Mario Díaz and his colleagues reveal the differences in the risk assumed by different species. For example, larger birds run fewer risks, that is, they take flight at a greater distance, than small ones. The older a bird is, the more energy it consumes when taking flight and the slower they are when doing so, for that reason their flight distance is greater. Differences in behavior have also been detected depending on the activity that the bird is carrying out at that moment. A breeding bird follows the cost-benefit relationship that we have expressed, but when the same bird is in full migration it uses other strategies, for example, it optimizes the risk by grouping in flocks of many individuals. Large crowds allow better surveillance and better use of resources because while some watch others eat and, furthermore, the probability of being caught in the crowd is less.
These are just some of the ideas expressed by Mario Díaz during the interview that we offer today in Hablando con Científicos. I invite you to listen to him.
Mario Díaz Esteban is a researcher in the Department of Biogeography and Global Change of the National Museum of Natural Sciences, CSICand president of the Scientific Committee of the Spanish Ornithological Society.
References:
Peter Mickula, Mario Diaz et al. Adjusting risk-taking to the annual cycle of long-distance migratory birds. Scientific Reports volume 8, Article number: 13989 (2018)
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