Bald Eagles--Non-Audible Communication?

Or am I nuts??! I was very thrilled to get very close to a bald eagle with its nest and an eaglet not far away. As you can see in this shot, the bird (female?) appears to calling out loud, but no sound was heard... not this time, or in a dozen other instances when it opened its beak. OK, this may be a DUMB question to some... but can they communicate in a way that's not audible to us?? I mean, I've heard their calls many times... this just got me curious!!!!!

Really good 4th.

I'm not sure about "silent" calling, but I've heard plenty of loud eagle calls, as well as soft murmurings to chicks.
Was it very hot out? Birds "pant" in much the same way as dogs, and there would be no sound. Just a possibility.
Let's see what others add.
Sandy

If it was hot or evn unusually warm, I'd bet sandy's suggestion is spot on. Birds do pant by a process called "gular flutter" in which the mouth is held open and the floor of the mouth and pharynx flutter rapidly to increase the flow of air over the moist suface to enhance evaporative cooling. The only other circumstance in which I've observed a similar gape posture is in preparation to regurgitate "casting" of indigestible material which accumulates and is compacted in the stomach's muscular portion (gizzard) before regurgitation.
Dave Graham, East River, SD

Come to think of it, Bill, you're probably right about the non-vocal communication ! The message I get is "Damn; it's hot!"
Dave Graham

Thank you Sandy and David for the information! Well, I'm not sure about excessive heat--this was taken in Northeast PA on the morning of the 4th of July, somewhere around 8:30-8:45 a.m. Overnight temps were probably upper 50s/low 60s. At the time of the shot, it was kind of harsh light, with a white sky and fog/mist still in the air (as you'll see in one of my posts). The bird repeated this action numerous times as it perched in this tree.

After that, it flew about 80 yards away to the very top of another tree, where it stayed with wings spread wide open, intermittently preening and looking back at its offspring on the nest.

So I'm not sure, I'm pretty sensitive to heat at this stage (lol), and it wasn't that warm at this point. It did not return to the nest, and we were there for a good two hours. So possibly it had just finished hunting and feeding before we got there??? Or was it just "burping"?? Sorry, just trying to provide you all the info I can. Afterward, I got worried that there was something wrong with its ability to vocalize--but your points indicate that's probably not the case. Thanks, hope that info helps!!!

All birds communicate non-verbally. Posture, behavior, size, movement and eye contact all transmit a lot of information. If you've ever been around an active hummingbird feeder, you've seen how much silent communication can occur. It's no different with eagles, except that their excellent vision allows them to see cues we miss. Birds of North America says about Bald Eagles,

Aggressors use displays involving head motions (head and neck extend up and/or out), wing motions (raise wings above body at 45° angle above horizontal and flap), and crouch/squat, and usually vocalize or subvocalize to challenge feeding birds (Hansen 1986). Feeding birds may use similar displays to fend off aggressors.

If you are serious about avian behavior, I cannot recommend strongly enough a subscription to BNA.

This is why I asked here.

Just to follow up a bit more Jim, I often use the Cornell Lab of Ornithology guide as my main resource for anything avian--other times, I get lazy and just ask here, or email. It is a wealth of information, and I will sign up for the BNA. Besides the open-beak behaviors, the adult eagle always kept an eye on the youngster in the nest, even as it moved to another tree with its body facing the opposite direction, with wings spread wide open, preening and head turning toward the eaglet. Much appreciated everyone,

I've spent quite a few hours staking out eagle nests and have never noted this behavior with the silent open mouth. As previously noted, they do a lot of other forms of non-vocal communication and the parents definately coordinate their activities to feed and protect the little ones.

Hmmm... interesting. I don't know, I do know I have probably 10-12 different images with the eagle's in various stages of being open, without making a sound.

This is a very interesting post and thread. I have seen this "silent calling" behaviour many times while observing a Bald Eagle nest (3 eaglets) this spring. Another photographer has observed the same behaviour at the same nest. In fact, there was a bit of a discussion around this: inaudible calls, yawning, digesting....

I have seen this behaviour on cloudy, cool days and on sunny days. None of these days was overly hot. The "silent calling" seems to be associated with a sudden and enhanced state of alertness. For example, one time, there was a flight of pelicans approaching and the eagle in the nest got all excited and did this "silent calling" while looking in the direction from which the pelicans eventually arrived. The eagle on the branch near the nest took off and circled around. Once the pelicans had passed, the "silent calling" stopped. Another time, the parent (female, I believe) brought home a fish she had caught and landed on the nest above me. The only calls up to this moment were from the eaglets who must have seen their parent fly in with food in the talons. Shortly after having landed, the adult looked over the edge of the nest and saw us hiding below. I have a photo series (poorly exposed unfortunately) where the beak is closed, then it opens (surprise is evident in the eyes of the eagle), and then the beak opened completely in this "silent calling" mode. A few seconds later the eagle took off. No sound.

Based on these and other events, I believe it is a communication technique, whether it is truly the emission of sound waves (ultrasound or infrasound) or a visual communication method by adopting a calling posture ("Hey, I'm calling"). The body posture seems to be exactly the same as for normal, audible calls.

It seems to me that many of these "silent calls" happened when the eagles were in close visual contact and perched either in or on the nest or on a branch nearby. This being a static situation gave me a good opportunity to observe. I also have many photos of eagles circling overhead with their beak open and they were calling, i.e. typical audible calls. Whether there were also "silent calls" intermingled with the audible calls, I don't know. I was too busy tracking the bird to try to match opening of the beak with sound.

Thank you Roger, what great observations! It repeated this behavior over and over, and yes, the nest and offspring were in view at all times. Other than two us taking photos, I did not see any aggressors in the area, nor anyone disrupting them. That makes me worried that even approaching these birds/nests causes some sort of disturbance in them. ???

What you describe is spot-on with what I observed, and took many photos of. Thank you again!!! Bill