Chasing Crows

Observe, Log, Run

Mobbing

As I fist stepped outside this morning a bird flew overhead to the northeast. I noticed it and tried to ID it as is my habit to do. Not a crow, not a gull, not a pigeon. Its wings were short, white belly, and moving fast. A bird of prey of some sort I concluded. Briefly my mind went back to scenes of how the crows reacted to such an intruder during nesting season, but I figured that during the winter they’d have no real cause to fear this guy. A couple minutes later I heard crow calls, what I thought to be just the usual ruckus. I still haven’t had much luck in discerning alarm calls from their usual banter. I look around the tree line and find them circling a pine tree to the east. Then I see that tell tale swoop. One crow flies past the tree, arks up and turns back directly towards the tree. I wait for it to happen three more times before I’m satisfied that this is mobbing. There is something in that tree and I had a good guess what it was.

IMG_4318Coat on, camera, check settings, out the door in less than a minute. I walked down the street a ways and look through my lens. Yep, thats a hawk alright. I crossed the street to get a closer look by the time I get there the hawk has moved. The crows, still calling loudly, take up position in the newly claimed tree. After another minute the hawk is flushed out of the tree, I could just make him out from the crows that followed close on his tail. I’m forced to cross the street again, and by the time I got to where the crows had perched there is nothing to be seen of the hawk. I wait and look, but eventually even the crows become satisfied that the intruder has left. IMG_4320

Lesson of the day, mobbing does still take place even during the roosting season. Apparently Raptors still pose enough of a threat that the crows find it necessary to partake in this behavior year round. Additionally, I have to consider the possibility that I was unwittingly complicit in their “plan”. One part of mobbing in other species is to draw the attention of larger predators to drive away the smaller one. In a respect the commotion did in fact attract me to the site and it did seem that the hawk made itself more scarce after my presence than before.

Crow in Flight

Composite image of American Crow in flight

Composite image of American Crow in flight

Future of Project

IMG_8485Since last I updated the crows have gone into their “roosting stage” where the separate, territorial mating pairs come together along with their new young to join large communal roosts for the winter. This is a time that, despite having the potential of showing social interaction and interesting behavior, is almost impossible for me to observe during my normal schedule. Roosts form only in the dimming light of evening, high up in tall trees, and often cover several miles in a single night before settling. I did take note that the not fully matured calls of this years fledglings can still be heard amongst these roosts.

Now it about the time when the mating pairs begin preparations for nesting if they have not already. To my speculative eye it at times looked like pairs of crows were flying formation around my little patch of town. The response to bait place on the ground had been poor to non-existent. Perching in regular spots does occur with a group of at most 3 crows. I suspect that ground foraging and frequenting of key trees in this territory will increase as young hatch this season.

Which brings me to the disrupting news that construction will be taking place on the lot next to me. I cannot be certain what effect this will have on the crows that frequent this area. It will at least disallow me from putting down bait, and could in the worst care scenario drive away the resident pair. I’m sad to say, but at this point it looks as if I will be unable to carry out any more active experiments with these crows. I will try to keep record of what effects the construction has on their habits.

Feeding Fledglings

As chance would have it the odd calls returned this morning in much the same way they had the previous. Now with a hypothesis to test and an idea of what I was looking for I went out to check on the crows. At first it was about as difficult to  interpret as the previous two times, but then I got a good look at the mouth of the crow sounding the odd call. A beautiful pinkish red marked the lining of the mouth of this bird showing that it was a juvenile. To add to that the eyes where still the milky blue-gray of a fledgling. All that tied with the calling could have been enough to conclude that this was begging behavior but I was lucky enough to catch the actual feeding it’s self.

The begging call appears to be prompted by the sight of food in the parents bill.

 

The blue-gray eyes eventually turn dark brown-black with age. The Mouth lining turns black with age as well.

A second fledgling showed up to feed. The parent ignored the pleading of both and took the opportunity to feed it’s self.

Interestingly enough it looks like both the fledglings are quite adept at flying. I was surprised by this as I did not know they developed that ability this early in the year.

Odd Calls

On two occurrences in the past two days of observation a crow(s) has been making a unique call I have never heard before. The first time was in the early afternoon from two crows in the tree designated N1. Looking as close as I could through the maze of branches it looked like one was perched on a branch and the other was close by hopping in closer to the first. From what I could see the first had a food wrapper of some sort that it was working over for the residue left on it. I don’t know which crow was giving the strange call, but I might assume it was the one not occupied with the food wrapper. After several minutes of almost uninterrupted calling the second crow flew away and the first continued to work on the cellophane wrapper.

The two days later I heard similar calling and went to investigate. Its very difficult to spot crows in trees now that the foliage is so dense. I did see two crows in N1 gain this time one of them had a very large ( probably two inch diameter) round object held in its beak. Again I could not make out which crow was responsible for the calls.

I did not get another clear view for quite a while until well after the strange calls had concluded. later two crows came to the ground behind the gas station.

At this point there was quite a bit of regular calls and scolding likely directed as a squirrel just off frame. Eventually one flew off followed by the other. Then a previously unseen third crow flew after them from a near by tree!

My interpretations of these events are split. I have not found anything that fits the description of the calls I heard exactly, but the closest thing I could liken them to is juvenile begging calls. The presence of a food item in both cases certainly supports this concept. Additionally the presence of a third crow means that the resident pair could have young.

However, In both instances the crows took off flying after their interactions. It is likely too early in the year for a fledgling to be  flying with its parents in such a way.

Now that I know to look for the presence of a fledgling or juvenile I may have better luck understanding these types of interactions in the future. However, as is often the case, there is not promise that I will ever see this behavior again.

 

Strange Food

From my reading in a couple different sources I think it is safe to say that corvids have to learn what is edible. Now this learning could take either the form of watching parents and compiling a list of all available foods in an environment, or something more sophisticated such as experimenting with new items to test their edibility. Importantly it is very unlikely that crows have hard wired list of edible food that the refer to when foraging.  If they learn from others what is good to eat then they should not readily eat something novel that they have never encountered before. Conversely if they test all possible food items they are likely to show little discrimination even with items they have never seen previously.

Considering that resident pair are probably well acquainted with the cast offs of human life, they are likely used to eating a good number of common food items. Even if they had a finite list of edible things and adhered to it strictly, it might be quite a task to find something not on that list. Common things such as fast food, nuts, fruits, breads, and meats are all likely common fair for these ominousness scavengers. In congruence with this they have already shown them selves adept at scavenging from fast food packaging litter.

Now if it is in fact the case that crows have the ability to test new candidate food items then there is a new set of questions that must be asked. Do crow test all things as candidate food items at one point? What are the criteria that an item must fit to be considered a candidate food? What attributes make existing food item appetizing that could effect what candidates are tested? What attributes inform the crow’s decision once it has tested the food?

To begin narrowing down the wild number of questions I began running the Strange Food experiment. The first stage of this experiment consists of little more than attempting to find a food item the crows will not eat. So far I have yet to find an edible item that the crows have not only tried but taken large portions of. In the list so far is:

  • Unsalted sunflower kernels
  • Unsalted green pumpkin seeds
  • Unsalted almonds
  • Unsalted peanuts
  • Salted peanuts
  • Salted ridged potato chips
  • Salted French fries
  • Salted Frito corn chips
  •  Wasabi  peas

Of these items the pumpkin seeds seemed to garner some added enthusiasm from the crows, but as each of these items was placed out serially over the course of many days this likely means little in the way of preference.

Breaking a Wasabi Pea in Beak

The wasabi peas were the most interesting of the tested food items so far. During this whole process most of the food place out was taken by squirrels rather than crows. The wasabi peas however, were rejected by the squirrels and only eaten by a crow.

The crows acceptance of the wasabi peas more importantly is evidence on the side of crows testing new food items. While its not impossible that this particular crow has had prior experience with this exact food item, it is far less likely than any other tested so far. The best explanation is that the crow ate something that was not familiar to it.

The wasabi peas are also important in another way. Their flavor is considerably different from the other food items tested. While they are not necessarily spicy they do have a distinctive flavor and scent. Likely it is this flavor that caused the more scent oriented squirrel to reject them.

New Lens

 New Lens means better observations to come! Next up is the strange food experiment.

Food Identification and Foraging.

One of the major questions I have had since the start of my observations with crows pertained to their ability to find and identify food. I was impressed at how quickly the crows found and made use of the bait I put out during the measurement experiment and I wanted to know more about how they identified food. Could they see it from the air or did they need to be close to the ground? How did they know what was edible and what wasn’t? Could I modify how easily they found the food I placed?

There is some actual study on this subject and some basic facts are already known about it but I wanted to both confirm those results for my self and possibly probe deeper into the question. In every experiment done with corvids where food is involved, that food must be visible to provoke behavior from the bird. Experiments where the bait is hidden are rarely if ever successfully solved by the bird. This leads to the conclusion that Corvids require visual stimulus to identify food. This is a fact that has been largely born out by my own experiments as well.

After having performed approximately two weeks of openly feeding the crows in one spot I switched my approach. The first iteration of  the covered bait experiment involved three “baits”. One bait was placed in a cup, covered by a sheet of dark paper, and placed to one side, the next bait was placed in a similar cup, left uncovered, and placed in the middle. The third “bait” was a control consisting only of rocks in a cup placed to the other side of the “open bait”.

The hypothesis of this test was that if the crows required visual cues to find food they would not attempt to check either of the covered baits but would still eat the open bait. If the crows used smell or some other sense to find food they would likely check both the open bait and the covered real bait but leave the control alone. Lastly if the crows used a method that did not rely on any sensory stimulus to identify food, but rather investigated all possible food sources they would likely check all three baits.

The open bait was placed to acclimate the crows to the new configuration of the feeding sight. Every time new items are placed the crows must be given time to feel comfortable with the change. Addition of freely available food ensures that they return to the sight later to engage with the experiment. This was also the first time the bait had been contained rather than scattered on the ground and I wished to ensure that this was not a confounding factor.

This first rendition of the covered bait experiment had its fatal flaw in the paper used to cover the food. Due to windy conditions the paper would from time to time move or flap while the crows where near and scare them off. Once the open bait was gone the crows did not venture near the experiment again.

After the relative failure of the first experiment I decided to approach the  problem in a more incremental way. I wanted to ensure that a crow could even access covered food if it was so inclined. I reproduced the first experiment but this time used clear plastic covers ( the kind you get from a spindle of blank CDs). On the left was the covered bait, in the middle the open bait, and on the right the control rocks.

The hypothesis was similar to that of the previous except that it did not control for visual stimulus. All three baits were visible and the crow would be likely to investigate the two real baits or, far less likely, all three including the control.  If the crows did not investigate either the covered bait or the control it would show that the crows would not or could not access covered bait under any circumstance.

This version of the experiment went comparatively well. After a short one day acclimation period the crows finished the open bait. The covered bait was eaten twice in the next two day period but I never observed this happening. On the third day of the experiment I finally observed a crow attempt to remove the cover.

11:55 crow knocked cover off of bait by pecking repeatedly at it. Pecks were aimed largely at the top of the cover and did not seem directed towards moving the cover so much as getting to the peanuts.

12:00 replaced cover

2:55 high 5’s from the north out of sight alerted me to the crow. I eventually found it perched on top of the gas station and watched it swoop down out of sight then walk up to the bait. the crow first picked up a single peanut that was laying outside the cover from last time then walked around a bit. Shortly after the crow moved to the left side of the cover, crouched down and gave it a sharp push with its bill. this moved the cover and the cup of food inside over quite a bit but did not remove the cover. the crow made several more attempts from different angles, stopping from time to time to eat what must have been loose peanuts freed by his efforts. after several failed attempt the crow left having eaten only 3 or four peanuts.

4:49 ground foraging in the yard

5.11
8:02 crow attempted to get to bait by pecking at the sides of the cover again but failed. left after extracting only one or two peanuts.

8:30 a squirrel had no problem uncovering the bait by pushing down and pulling back on the top of the cover. The squirrel ate at the bait for about 15 minutes, during which time a crow appeared. The crow waited until the squirrel would walk away to move in and take bait at which point the squirrel would chase the crow away. The crow cached most of the peanuts it collected in the strip of dirt nearby.

9:40 crow came to bait and pecked once at the cover. Then the crow grasped the top of the cover in its bill and lifted it off and threw it to the side.The crow stashed multiple peanuts in its gullet and continued to collect more until its bill was full as well. Then it flew off to the north.

From this point forward the crow(s) became increasingly successful at removing the cover from the bait. Interestingly, despite the immediate success the one crow had with lifting the cover off this strategy was only attempted one more time days later and was otherwise overshadowed by pecking at the cover violently until it fell off.

Another item of note was the crows’ apparent surprise at successfully removing the cover. They almost always were startled into flight when the cover was finally knocked off.

Crow is startled by movement of the cover it just managed to knock over.

My second attempt at the covered bait experiment built off of the success of the clear cover experiment. The setup was similar to the previous two experiments but now the covers had been made opaque. I taped construction paper to the insides of both covers so that nothing could be seen inside but the outside remained unchanged. I again introduced the open bait which was eaten reality and then allowed the experiment to sit.

At no point during this phase of the experiment did a crow attempt to interact with either of the covers. As an unexpected control, a squirrel proved that these opaque covers where no obstacle to a more scent oriented species by repeatedly raiding the covered bait. Once the cover was knocked off the bait a crow would appear and the squirrel would have defend its catch. It became obvious that the crows were responsive to food when it could be seen but did not make any connection between the covers and food.

In an odd twist the squirrel showed the most interesting behavior of this experiment. On one occasion after having knocked the cover off the bait and finished eating all that was available the squirrel attempted to remove the control cover that housed only rocks. While it is possible that the control cover had absorbed some food scent and the squirrel was merely reacting to that, I find it equally possible that this is an example of an investigative foraging technique.

After a full week of this covered bait experiment I returned to the clear cover experiment to confirm the results. Within several hours a crow had returned to the feeding sight and deftly knocked the cover from the bait. This time the crow stashed the food in it’s gullet rather than eating it on the spot.  Not ten minutes later the (possibly same) crow returned. What happened next, although only anecdotal, was the best evidence I have seen that crows use visual stimulus to identify food. I had switched the positions of the control and the bait at the beginning the day. When the crow approached the control cover it stopped, looked in briefly, then moved to the true bait and knocked the cover off.

Another observation that may show further complexity in foraging  happened unexpectedly over the course of three days. In the evening I parked my car over a piece of garbage, a takeout box. The day after next two crows (likely the residents) where rummaging under my car for left over food. This is an interesting observation because my car should have acted like the opaque cover in the covered bait experiment. It may be that the crows could see the food or even the take out box (which any seasoned urban scavenger must associate with food) and decided to go get it. This, however, would have required that they be on the ground in very close proximity to my car to see it. It seems that the crow’s ability to find food is quite extensive and it’s exact limits still illusive.

Measurements

My next step in investigating the life and behavior of my neighborhood crows was to take a couple of measurements if at all possible. I set up a board with markings at 4 inch intervals, both vertically and horizontally, set out some peanuts, and waited. The first measurement trial lasted 3 days and netted a total of  8 separate instances of crows feeding in front of my measuring board. In the last day of measurements two crows, most likely the resident pair, showed up for feeding simultaneously giving good opportunity for comparison. I still only counted the pair feeding as a single instance.  The days’ proceedings went as follows:

5.2
10:05 instance with no measuring board
10:26 placed unsalted and measuring board
10:30 single crow feeding
2:30 single crow feeding
3:10 single crow feeding
3:13 placed unsalted peanuts

4 feeding instances
4 crow sightings

5.3
9:42 placed unsalted peanuts and measuring board
2:05 single crow feeding
3:40 placed salted peanuts
1 feeding instance
1 crow sighted

5.4
6:45 two crows feeding
10:00 placed salted peanuts
1:36 two crows feeding
1:39 placed salted peanuts
2:29 single crow feeding
2:30 placed slated peanuts
3:39 two crows feeding
3:59 placed salted peanuts
4:24 single crow feeding
4:53 single crow but no bait left.

5 feeding instances
9 crow sightings

The time between feedings ranged anywhere from 4 hours to 4 minutes from the previous feeding or dispensing of bait. There was not an observable display of preference between salted and unsalted peanuts. Higher frequency of  feeding, as well as feeding in pairs, indicates that by the third day the crows had grown more comfortable at the feeding site.

This method of measurement failed to give any fine grain information. All crows measured, at least two distinct individuals, measured roughly the same in length (~16 inches from tail to bill at a 12 degree angle) and hight (~8 inches while standing at alert, body at a 40 degree angle). If any measurable difference existed between these birds it was obscured by the variable nature of posture as well as distance from the measuring board.

 

For long notes of 5.2-5.4 download 5.2 – 5.4 LongForm

4.27.12 – 5.1.12

4.27

6:25 Went with my friend on to check out Mills pond area on a whim. As we walked through we quickly noticed a flock in roosting in a tree and performing the “paired dive bombing dance”. Eventually they moved further east to the roof top that they had occupied the previous time I witnessed them out there, then off out of sight.

I have fashioned a hypothesis on the paired flight that fits what I know about flocks. To the best of my knowledge members of a flock are not in any sort of pair bond or actively mating. While they could possibly have ‘friends’ it seem unlikely that this has anything to do with that. The flights also don’t seem like proper fights because they begin spontaneously and end just the same. Also multiple birds, if not every bird in the flock at some point, engage in this behavior. My speculation is that it is a form of social jockeying or perhaps even more specific, jockeying for a perch. One bird will initiate the chase to challenge a bird for their perch and if the challenged bird pulls out of the chase their perch is forfeit. This is just a hypothesis, so I need to get more footage of the event to solidify things.

[Updated] Bernd Heinrich described a behavior similar to this displayed in ravens in his book “Mind of the Raven”. He chalks the behavior up to play rather than any direct social or survival function.

4.28

10:00 I could see one crow atop G1. He flew off to westward over my building then returned and landed in parking lot. He quickly saw me and took off perched in N1.

1:39 top of N1 single crow  giving calls in medium length 4’s 3’s and then 2’s. I could hear a crow to the west responding only in 2’s. Crow on N1 flew off to the north.

2:00-2:30 Went down to Mills pond and saw three crow. one landed on the ground and poked around for a while, that was it.

4.29

On my weekend I traveled about 60 miles north. I happened to spot a crow chasing another unknown bird as I was walking through down. I have to marvel at these crows that will so readily chase something twice their size.

4.30

10:56 Single crow perched on G2 giving long 2’s and 3’s in even pace with mild downward inflection. Remained perched for 1-3 minutes before flying off to another tree, then to the wooden fence. Second crow joins and they look over the north side of fence. Newcomer is likely one giving calls in 3’s similar to before. First crow gives short high 3’s in a sort of kek-kek-kek fashion. during this another crow flies overhead. Second crow jumps down behind fence followed by first. I run around the block to get a better view. from my view at home I can only see the outer side of the wooden fenced in area. from around the block there is a building in the way. A sign says beware of dog on a gate to the fenced in area. One of the crows jumps back up on the fence. Just then I notice a white and black cat sauntering along and watch him slip under the gate and enter the fenced in area. Loud long rapid calls probably in 5’s but really not grouped, erupt from the fenced in area and one crow flies up over the roof and back to perch on a nearby tree with the other crow. Undoubtedly this is an example of alarm calls. The key features as I can tell are the rapidity and the lack of grouping.

12:36 One crow perched in G1 giving long 3’s another unseen crow to northwest gave short high 3’s “Kek-kek-kek”. Two perched on tree just above wooden fence and gave series of low calls in no particular grouping. one flew off to east, other left unseen.

1:42 single crow on SE1 giving long 4’s. flew off to N3 then out of sight northbound.

2:48 flying west to east with something in its bill

3:15 perched on tree above wooden fence cawing pretty much incessantly until retreating some minute later to N3, then N1 then to G1 to eat some small piece of food carried over from at least G3 if not near the wooden fence. Ate food in several bites, ruffled feathers then moved further east to another tree. hopped around that tree for a few seconds then made off towards the east out of sight.

4:04 individual on G1 giving medium length calls in rapid succession in 6’s or more. flew over behind gas station, then to N3 then off westbound.

4:18 flew in from east, perched on N3

4:30 Complete confusion. I could see a single crow perched on G2 then other crows fly in from east. One Crow flies through the area between N1,N3,G1,G2 as if being chase but I cannot see any other birds. A Crow perches on N3 and gives some calls, then flies over to tree above wooden fence and gives the old long-short-short call. Some noise can be heard from neighbors but nothing can be seen. Yet another crow flies through and the crow perched above the wooden fence takes off. Next I saw a crow perched in G2 hopping around a bit. A Squirrel, probably surprised by the crow, was doing its best to remain motionless. Eventually it tried to make it’s way back up the tree. At just that moment the crow jumps over and picks of something in beak and flies away to the east.

6:30 My friend and I put together a board with measured markers on it to see if we could get some measurements on the crows that flock at Mills pond. Before we could even set up we spotted two crows in the marsh grass picking around. I attempted to see what they were picking out but could only get sight of a partially open bill holding something small. Wat ever it was it was no bigger than a marble and could be picked out of the ground and eaten readily.

We set up the board and placed three plastic cups containing salted peanuts, unsalted peanuts, and regular ruffle potato chips in front. We then moved about 20 meters away and waited in the grass. Absolutely nothing came to take the bait. A couple crows flew over head, and There was possibly even a small flock perched in a tree to the west, but that was the extent of it.

5.1

9:40 perched on E1 for at least 15 minutes, didn’t move around much

10:30 perched on tree next to E1 grooming and ruffling feathers, flew off north.

6:02 I heard calls but could not get a visual on any birds before they went silent. As I looked around I saw something, possibly a cat, move around the corner of the wooden fence and out of sight. I ran around the block to see if I could ID it but it was gone. On my way back a single crow flew over head from the north east and perched low on N1. I watched it for about a minute then moved around to the other side of the tree to get a better look. The crow moved up a branch or so and proceeded to ruffle his feathers and preen. I was close enough I could see how drenched this bird looked. It is a bit of a reminder that these birds have to rough the worst of the weather with no protection at all.

8:00 Saw two crows flying in from the west. One of them perched on a low branch of E1. Eventually three, though I’m not sure where the other two came from, took off to the south east. I followed through the park and then further south. I found a good grouping of them roosting in a tree, probably 20-50 birds. There where some vocalizations ranging from low to high among different birds, but most calls where in groupings and seemed pretty tame and undirected. Some of the birds surprised me with their shear volume.

A loud noise from down the street startled the whole flock and they all took flight at once. They moved westward as I did my best to follow them. The flock diverged and formed two groups that perched on either side of the street I was in. Slowly single crows would make their way back and forth, and at times whole trees with up to a dozen would empty out. they moved progressively northwest over the course of 5 minutes. They moved into an area that was inaccessable from the road. It appears that this was their final roost as they did not move from this spot for some time.

another pass by the mills pond area gave no sign of any crows, so it does not seem that the flock that has frequented their was around tonight.

Not to make the assumption that only one bird can perch on a given tree, but I do believe that its a good guess that the bird that perches on E1 is a repeat character. If that was the same bird that perched their tonight and then joined the flock, that would confirm that this bird is unattached and not one of the local mating pairs. This is circumstantial, but its all that I have to go on for now.