You ask Karl: “But what if it’s just the same bird, calling again and again?”

He is not impressed by your question. He takes a deep breath and explains how he compares the amplitude of four-channel recordings to estimate the location of the calling birds.

What if the birds move around? You don’t ask him about that.

“We need to develop standardized methods for estimating the density of calling animals.” You look confused. “We still need to improve the algorithms”, he explains and logs into his computer. “For that I use… ah… Okeeeey” Click, click, click! An image. Click, click, zoom in, click click, “still not…” Not What? “But you could hear a bit?” You say yes just to please him. “Of course it depends on if there are clear differences within the individual species. The frequency and…”

What he is trying to say is that each and every single animal has a unique voice. There is a brief moment of silence and then you let out an almost silent, but still necessary “Ah.” Karl’s fingers move swiftly across the keyboard, click click, and the computers let’s out a ding, ding alert sound. “Aaaaahh, ok” Ding, ding, ding. “A perfect match!” “How do you see that it's perfect?” A click, and then eye contact. You still look confused. “There is a time delay.”

You are frozen, pleasantly stimulated by the smell of old documents, the clicking, the singing birds and the persistent chorus of explanations. “It often occurs when there are long term recordings,” click click, zoom in, “maybe here, at the beginning,” click, click, “all except,” click, “that is marked,” click, click, “Sample1.”

“Yes.”