I am going to share a few pointers based on my observations made over the years on signs of stress that owls may reveal. Please note that it is hard to interpret what an owl is doing from a single photo so do not take these pointers as absolutes; they need to be used in trying to assess the whole picture as much as possible. Context is often key. The intention here is to get people to think about looking for behavioural clues when they are lucky enough to observe an owl in the wild. Furthermore, there are some situations where the observer is not the cause of stress as a few of the following examples will show. I have tried to talk about the features one by one below, but also remember to look for the combination of different clues and overall behaviour.
You can learn a lot about an owl by listening to their song and calls. Owls of course signal to each other and other animals vocally. Owls have a repertoire of calls, in addition to their “song” (song is used in territorial defense and advertising and is what we humans hear most often). Imagine a situation where a nest predator such as a raccoon is approaching the cavity nest of an Eastern Screech-Owl – obviously a stressful situation. The screech-owls will make a few single-note calls at the first sign of danger (quite unlike their A-song or B-song). These may proceed to a series of 3, 4 or 5 single notes, often on a descending pitch: oooh-oooh-oooh-oooh. I have sometimes seen human observers ignore these subtle and soft calls. I even once had to intervene when a nonchalant dog walker was about to be whacked in the head. If the danger persists, the single note calls will sound increasingly agitated and start to sound more like a bark. Barks may be accompanied by whinny calls and aggressive rattle calls, especially as the owl switches from a defensive to an aggressive position. Some owls give a very cat-like call as well. If the perceived intrusion persists, the screech-owl starts clacking its bill and shortly after may strike or dive-bomb the intruder. If you notice any vocal behaviour along the gradated scale, and if you suspect that you are the perceived intruder, then back off sooner rather than later. If you hear bill clacking, you’re already at the high alert stage.
VISUAL CLUES:1) The Eastern Screech-Owl (Winnipeg, Manitoba) in this photo is highly stressed. Before you read on, take a moment to look at the photo for any clues. This bird is in the situation I described above – a raccoon approaching their nest. At this point, the male has signaled to the female with a few single note calls and she has come off the nest. About 5 minutes later, in what looked to me like a coordinated attack, the male flew in front of the raccoon and then the female whacked the raccoon on the back of the head with her talons—a bold and risky manouevre that may have saved the lives of their 5 nestlings. I know this owl is stressed from the context but there are a couple of visual clues in the photo too. Note the fairly stiff and erect posture of this owl with the ear tufts close to fully extended (not complete because this is fairly early on in the proceedings – I put my camera away after this so I could observe). This is sometimes called the “tall thin posture” and owls use it in a variety of contexts including as a way to make themselves look less visible to a potential threat but also in direct response to some threats. If you are observing an owl and notice the body posture change to become more elongated (“tall and thin”) then I would suggest you back up and give the owl more space. On species with ear-tufts like this, the position of the ear-tufts is an added clue. The tall thin posture doesn’t always mean the same thing but you should be on the look out for it.
2) This roosting Eastern Screech-Owl (Winnipeg, Manitoba) is also in the tall thin posture. This bird is trying to avoid detection by some noisy pedestrians on a popular suburban trail. You can see how stretched the body looks and even though the ear-tufts are partially hidden, you can also see that they are raised. This owl is using another trick too – “squinting”. Squinting refers to the practice of almost closing the eyelids so that the owl’s eyes are barely visible but still permitting the owl to see. This seems to be most prevalent in species with yellow eyes (perhaps because yellow is an obvious break from their otherwise brown/grey colouration) but it is not exclusive to those species. It is presumed that this behaviour is an attempt to avoid detection by a potential threat. This is subtly different from having the eyes closed (owls are certainly not opposed to closing their eyes for a daytime snooze). If you see an owl with open eyes and notice that the eyes appear to be closing or squinting then the owl has seen you. It is wisest to give the owl some space. Never risk scaring an owl from a roost site in the day as this costs them energy and may expose them to mobbing. This may make them vulnerable (especially small owls).
3) This female Great Gray Owl is highly agitated by an intrusion near their nest site that she perceives as a threat to her chicks (Great Gray Owls on the nest must be vigilant for black bear, ravens and other threats). Great Gray Owls don’t have ear-tufts but you can see one key sign of stress in this bird. Look closely at the rictal bristles (the long thin feathers at the base of the bill). These feathers normally fall over the nostrils to protect them from dust but they are raised here leaving the nostrils clearly visible. This clue may be subtle and is not always easy to see under field conditions, but it is a key indicator! If you see this behaviour, back off immediately! An owl in this state of alert may seem to be “frozen” and may remain motionless for quite a long period but never mistake that lack of action for tolerance—this owl is not happy and could even choose to attack.
4) I was walking on a narrow trail in eastern Manitoba when I came around a sharp bend and surprised this Great Gray Owl perched on a fairly low branch above the trail. We were both surprised as we found ourselves suddenly face to face. Since I had my camera in my hands I took this photo (two versions: first full and then heavily cropped) as I backed up. In fact I backed up a fair distance and retraced my route to avoid causing the owl to move. This owl’s head has turned 180 degrees and once again you can see the raised rictal bristles. This told me immediately that I had startled the owl. I was lucky on this occasion as the owl didn’t leave the perch and seemed to settle back down once I had backed away.
Here is a crop of the same photo:
5) Though some may assume otherwise, this Boreal Owl in southeastern Manitoba (photo heavily cropped) is actually not stressed. The rictal bristles are relaxed on this bird and the posture is “normal” (the owl’s leaning forward has to do with focusing here and is not a sign of aggression in this case). Basically, this bird is hunting—listening and looking at a chickadee in fact. A few minutes after I took this photo, this owl flew out and tried to capture that chickadee but failed. A Boreal Owl would not normally attempt to catch a chickadee in daylight so this bird must have been fairly hungry to attempt it. The posture of this owl shows intense focus. The owl is leaning forward and positioning their facial disk in order to best pinpoint their target. In this case the owl was following the chickadee visually but owls also frequently move their head to facilitate pinpointing sound acoustically (especially those species with asymmetrical ears).
6) This Snowy Owl (Oak Hammock Marsh, Manitoba) is stressed and it isn’t hard to figure out that the cause of this stress is aerial—a Peregrine Falcon to be precise (probably stressful for most birds). In the case, because the threat is from above, the posture is very revealing. The Snowy Owl appears recoiled like a snake before striking… any animal that recoils defensively in this way is usually getting prepared to turn defence into attack. This Snowy is prepared to do a full back flip, talons pointed skyward, to ward off the stoop of the falcon. Snowies are of course a Bubo species and very closely related to the Great Horned Owl. They have relictual ear-tufts which even show occasionally in these types of circumstances (other round-headed owls can also raise the feathers on their head or raise the top of the facial disk). You won’t see this same posture in response to an intruder on the ground but there are still a few clues to look for such as the raised mantle feathers. Notice this Snowy Owl’s “fluffed” feathers and how the wings are held slightly away from the body. This can be a sign of a defensive posture and a way that the owl attempts to make themself look bigger to the intruder. Look also at the eye of this bird - - the constricted pupils could be another sign of this type of aggressive posturing (stress can cause pupils to constrict, dilate or "flash" between the two). When you see this type of combination, take it as a clear signal to back off. If you see these signs you know that something is bothering the owl.
7) This Barn Owl (Yorkshire, U.K) is stressed for another reason…. OK, just kidding!
Looking for the combination of the above postures and vocalizations may help you in your observations. Thank you for your time and patience and thank you for being observant and considering the best interests of the birds you observe!