<picture> and <source> tags

[allesan]

When using these tags inside image gallery with thumbnails like this

<li class="splide__slide">
    <div class="splide__slide__container">
      <picture>
            <source type="image/avif" srcset="image.avif" />
            <img src="image.jpg" itemprop="image" />
      </picture>
   </div>
</li>

in browser network tools I see that both jpg and avif files get downloaded. Is this expected behavior and why? Is there a way to avoid this?