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Message:

> They live in caves, go out at night, have sharp vision and use echolocation:
> 
>  https://cosmosmagazine.com/biology/the-dark-adapted-bird
> 
> "The oilbird (Steatornis caripensis) lives in colonies in caves in the north of South America. The birds prefer the darkness – when they leave the caves to find fruit to eat, it is at night.
> 
> "To live in this dark environment, oilbirds not only have extremely sensitive vision but also an excellent sense of smell, bristles near the beak for tactile sensation, and – like bats and some marine mammals – the ability to use echolocation to hear the contours of their surroundings.
> 
> "Each of these senses is a powerful tool, but they become even more powerful in combination. 
> 
> "A new study published in Royal Society Open Science shows that they adjust their echolocation techniques depending on the amount of light available so that vision and echolocation work together to produce information about the bird’s surroundings."
> 
> Abstract of study:
> 
> "Oilbirds are active at night, foraging for fruits using keen olfaction and extremely light-sensitive eyes, and echolocate as they leave and return to their cavernous roosts. We recorded the echolocation behaviour of wild oilbirds using a multi-microphone array as they entered and exited their roosts under different natural light conditions. During echolocation, the birds produced click bursts (CBs) lasting less than 10 ms and consisting of a variable number (2–8) of clicks at 2–3 ms intervals. The CBs have a bandwidth of 7–23 kHz at −6 dB from signal peak frequency. We report on two unique characteristics of this avian echolocation system. First, oilbirds reduce both the energy and number of clicks in their CBs under conditions of clear, moonlit skies, compared with dark, moonless nights. Second, we document a frequency mismatch between the reported best frequency of oilbird hearing (approx. 2 kHz) and the bandwidth of their echolocation CBs. This unusual signal-to-sensory system mismatch probably reflects avian constraints on high-frequency hearing but may still allow oilbirds fine-scale, close-range detail resolution at the upper extreme (approx. 10 kHz) of their presumed hearing range. Alternatively, oilbirds, by an as-yet unknown mechanism, are able to hear frequencies higher than currently appreciated."
> 
> Comment: an amazing adaptation perhaps created gradually by epigenetics.