by Māris Strazds, PhD
July 13, 2021
For the past 40 years, ornithologist Māris Strazds has conducted research on Black Storks, large migratory birds who nest in old-growth trees in forests in Latvia and elsewhere in northern and central Eurasia. Because breeding Black Storks require large, mature trees for their nests, the fate of this species in Latvia is tied to that of forests, and specifically to whether mature trees are protected, or not. Understanding Black Storks’ responses to Latvia’s changing forests provides important insights into conservation prospects for this and other species that depend on mature trees, such as many woodpeckers and raptors, in order to raise the next generation of birds.
A Black Stork forages in a shallow river.
When I started researching Black Storks in Latvia back in the late 1980’s, my aim was to show that the Black Stork was not as rare a species as was commonly thought at that time. It was true then, but as the saying goes, "no condition is permanent." Both the economic and political situation changed drastically after Latvia gained independence in 1991. Land reforms implemented from 1993 to 1996 and the intensification of forestry caused significant changes in the Black Stork population, as my research has found. In the past 20 years, the conservation status of the Black Stork in Latvia has changed from Least Concern to Critically Endangered. The main pressure behind this change is clear; it is intensive, and careless (despite being called "responsible") forestry. Many other factors contribute too, such as contamination from chemicals such as DDT and mercury, which decrease storks’ nesting success, and a significant increase in the population of White-tailed Eagles, as eagles are predators of storks. In addition, the depletion of storks’ food resources is being driven by the expansion of so-called “green energy” infrastructure, in the form of small hydroelectric power stations, which are destroying many of the rivers that make up storks’ best foraging habitat. Last but not, the least growing level of human disturbance can interfere with storks’ foraging opportunities.
A camera trap photo shows a Black Stork pair at a nest responding with alarm to a nocturnal threat.
In 2011, my colleagues and I started to use camera traps (trail cameras) at nests to check for ringed (banded) adults, which allows us to track individuals through their unique ring numbers. While identifying individuals in this way remains one of important aspects of this research, using multiple cameras at once has resulted in some big surprises. For example, we have discovered that multiple birds may use same “non-active” nest, that individual birds may appear at different nests, some of which are very far away from each other, during the same nesting season, and that there is a high number of extra-pair copulations (what would be considered “cheating” in human relationships), to mention just a few. Based on these discoveries, it seems that the idea of a "non-breeding pair" of Black Storks is a fiction, and even a breeding pair exists only as long as successful breeding takes place. If a clutch of eggs in a nest is destroyed, for example by a nest predator early in the breeding season, the pair of parents "divorces" in response. In addition, trail cameras with infrared sensors show how often birds are disturbed by mammalian predators, such as pine martens, at night, as shown in the above photo.
Ornithologist Māris Strazds leans against an old-growth tree that carries a Black Stork nest high in its branches. Like many raptors, storks may use the same nest for many years.
Because the birds detect approaching predators at night by sound, anthropogenic background noise – such as from traffic on a busy road nearby, or of a forest harvester operating at night – may lower their potential to detect predators and defend themselves and their nests. To understand the magnitude of this problem, this year for first time we installed a sound recorder at a nest as a pilot project. This nest successfully produced chicks, and now we plan to install sound recorders at more nests. If we can record sounds over the entire nesting season and match them to trail camera images, we may get some interesting results next year that can tell us whether background noise may be affecting the fates of storks’ nests. In terms of nest success, this year (so far) seems better than the last four, but the number of healthy chicks fledging (leaving the nest) is still very low compared to the long-term average, and the season is far from over. Food shortages during the second half of season may turn "successes" into nightmares, as unfortunately happened last year. This took place when the extensive river drainage systems encompassing many nests dried out and suddenly adults faced a food shortage – an "all food stores are closed" situation – so that many chicks still in their nests died from starvation.
By understanding what is happening with Black Storks, and the crucial factors in their struggle to survive and nest successfully, we can work to protect their remaining populations in Latvia and beyond. This species is a good indicator of the presence of old-growth trees in this part of Europe, so efforts to save this species should benefit many other forest-dependent species in this region as well. Readers can learn more from a new documentary film, “Mr. Black Stork” (Latvian title: Melnā stārķa kungs), which follows some of this recent research: