Why don't storks migrate anymore?

Through San Blas you will see the stork; if you see her, year of goods; if you don’t see it, year of snows.

Some Pennsylvanians believe that someone who claims to understand the Woodchuck language relays a message to the town every February 2 from Phil , a male woodchuck over 130 years old. The question is whether or not he has seen his own shadow, and thereby predicts six more weeks of winter if he sees it, or an early spring if not. Similarly, in Spain we have our own weather superstition in the form of a saying . Except that in our case, the protagonists are the storks, not one in particular, but any, and it falls the next day.

Of course, if we assume that the proverb has the consequences of a snowy year, they are disastrous. With late snows, planting is delayed, and with it so is harvest, putting livelihoods at risk for the coming winter. The year of snows is opposed, here, to the year of goods, in a terrifying sense. In the rural Spain of yesteryear, the supposed consequences of not seeing the stork in San Blas could be one of the worst nightmares that the peasant could have.

This saying comes from a time when white storks , birds that very commonly nest in our cities, migrated up to 3,000 km at the end of summer to western sub-Saharan Africa, mainly to areas of Senegal, Mali and Mauritania. . They took a month to arrive, and after wintering, they returned to the Iberian Peninsula at the beginning of February, in time to see spring arrive from the exact same nest from which they left months before. And if they were late, according to the saying, it was a sign that the winter cold was going to last longer.

The main reason the birds left in winter was the lack of food here. However, this situation has been changing in recent decades. The increasing presence of landfills and garbage dumps provided the storks with new sources of food. Rather than fly thousands of miles across the Straits of Gibraltar and the Sahara Desert , they could afford to skip the trip. In a few hours of flight they have the food they need, and they can return to their nests sooner. This has a direct effect: it improves your survivability. It was not uncommon for many storks, on such a long journey, to end up dying. In addition, migration is dependent on weather conditions, and climate change like the one we are experiencing can also affect migration routes.

During 2004, a census of the storks wintering in Spain was carried out. Regarding that, in 2021 a new census has shown that the population is quite stable instead of growing, as expected. Once again, the answer may lie in rubbish, as the quality of its management has increased in recent years, and several dumps have been closed.

But that there is more survival among adult storks does not mean that this reduction in migration, or its causes, is something positive, far from it. It has been observed that while resident storks have more offspring and earlier than migrants, there is an undesirable side effect. Since the parents cannot feed the preemie chicks the food they normally find in the wild, they feed them what is found in landfills ; something that an adult stork can tolerate, but for which the young are not prepared. So the mortality in the chicks in these cases turns out to be higher. If adults survive longer, and there is no greater reproductive success, the end result is an aging population.

But in addition, migratory birds fulfill their role in the ecosystem, such as influencing pest control or affecting the dynamics of infectious diseases. The disappearance of these majestic birds in the wintering territories can have a serious impact on those ecosystems .

After all, although in Senegal or Mauritania snow has never been seen, we can accept the more metaphorical meaning of “snow” in the proverb. And if in those territories they are not visited by the stork, because it does not migrate to the south, it is also true there that if you do not see it, it will be a snowy year .

References:

Flack, A. et al. (2016) ‘Costs of migratory decisions: A comparison across eight white stork populations’, Science Advances, 2(1), p. e1500931. doi:10.1126/sciadv.1500931.

Gilbert, N.I. et al. (2016) ‘Are white storks addicted to junk food? Impacts of landfill use on the movement and behaviour of resident white storks (Ciconia ciconia) from a partially migratory population’, Movement Ecology, 4(1), p. 7. doi:10.1186/s40462-016-0070-0.

Massemin-Challet, S. et al. (2006) ‘The effect of migration strategy and food availability on White Stork Ciconia ciconia breeding success’, Ibis, 148(3), pp. 503–508. doi:10.1111/j.1474-919X.2006.00550.x.

Nourani, E., Yamaguchi, N.M. and Higuchi, H. (2017) ‘Climate change alters the optimal wind-dependent flight routes of an avian migrant’, Proceedings of the Royal Society B: Biological Sciences, 284(1854). doi:10.1098/rspb.2017.0149.

SEO/BirdLife (2018) ‘Where do storks go in winter?’, SEO/BirdLife, 13 November. Available at: https://seo.org/donde-van-las-ciguenas-en-invierno/ (Accessed: 24 January 2022).

SEO / BirdLife (2021) ‘Wintering storks stabilize in Spain’, SEO / BirdLife, 3 February. Available at: https://seo.org/2021/02/02/la-ciguena-invernante-estable-en-espana/ (Accessed: 24 January 2022).