In June, the Krkonoše Mountains briefly became home to the very rare Apollo butterfly. This butterfly is a relic from the Ice Age, and its natural habitat consists of sunlit mountain rocks with an abundance of flowering plants. It disappeared from Czech nature nearly a century ago due to the loss of its natural environment. Now, the Apollo butterfly faces an imminent threat even in our neighboring countries: in the Slovak and Polish Carpathians or the Austrian Alps. Their decline is also accelerated by climate change, as it’s simply getting too warm for them.
Conservation efforts to save Apollo
Our nature conservationists are trying to reverse this population decline by preserving its original habitats, but they are also working to create new, backup environments. Such a place has now been established in the Krkonoše Mountains. Since August 2022, intensive work has been done to clear the rocks, which will serve as a substitute habitat for these iconic butterflies. Soon after, the area saw the appearance of many flowering plants, and with them, butterflies such as the critically endangered small blue butterfly in Krkonoše, the swallowtail, the purple emperor, and numerous ringlets.
Testing the new habitat: Male-only butterfly release
It was time to let the site be tested by its future residents. For this purpose, a total of 100 males from a rescue breeding program were released, having already fulfilled their reproductive role, to live out their days here. Why only males, you might ask? Once each male fertilizes a female, he no longer has any purpose in breeding, whereas the females still need to lay eggs for the next generation and are essential for maintaining the population. If the release didn’t succeed, we wouldn’t be left with anything if we had released the entire population. The butterflies were numbered with a marker before release, both for monitoring purposes and to diminish their value to potential collectors.
Our method of releasing only males was met with skepticism shortly after being publicized. There were speculations that the males would search for females and leave the site, skewing our results. Today, we have processed data from repeated expert monitoring, and we can confirm that these theories did not hold true. Even in nature, male butterflies naturally hatch a few days earlier than females and must wait for them. The males behaved entirely normally on the site throughout the three weeks of regular monitoring, with no observed “flights” away from the site, and they remained quite vital for a long time.
Positive behavior and site attachment
The butterflies exhibited their typical behavior, including active patrolling, territorial battles with other males, and most importantly, spreading out across the site and evenly occupying the entire area with frequent contact among each other. This is crucial for them because, as has been observed in practice many times, this phenomenon leads to a stronger attachment of the butterflies to the site. In human terms, their logic says, “There are a lot of other butterflies here, so there must be more females too, and I like that.” Of course, in this case, we tricked the poor males a bit. However, the positive monitoring results indicate that the Apollos didn’t catch on to our ruse.
In summary, the monitoring showed absolutely great results, so we can consider the management part of the project focused on the adults to be successful (though not yet complete!). However, this is not the end of the story, as there still needs to be enough space provided for the Apollo butterflies’ host plants. This is another reason why we haven’t yet released the butterflies in full; everything must be perfect for this demanding butterfly to thrive in the Krkonoše Mountains.
