Where Are You Going, Crows?

Hello Jane and All Other Bird Lovers,

Lately I’ve been stumped when people ask me ‘What’s with all the crows these days?”  Like me, they are astonished and mystified at the huge numbers of these darksome creatures that sometimes, especially at sunset, seem to be taking over the skies here in Santa Cruz.  (Spoiler alert: It turns out that crow populations are not increasing nationwide nor is a Hitchcock nightmare about to descend upon us.)

10 crows in tree
Crows gathering in pre-roosting site,  February 4, 2018, photo by B. Riverwoman

I decided I had better do a little online research and also pay closer attention to the actual crows around me!  Here’s what I discovered when I googled ‘Why are there so many crows?’  First of all, the huge concentrations of crows  is a five-month winter phenomenon, starting sometime in November and ending in March when the crows disperse to their individual territories to start building their nests and raising their young.   Add to this the fact that large flocks of crows head south each year from Canada for the more hospitable  winter climate of the states, adding large numbers to the ranks of local crows.   Further add to this the fact that crows are wonderfully communal creatures, mating for life, and even depending on first and second year non-breeding siblings to help raise their new broods.  During breeding season they are isolated from the rest of their clan .  But once the kids are raised,  I like to imagine,  the crowd-loving crows all get together in  raucous celebration of their temporary freedom  from childcare responsibilities and in joy at hanging out with the rest of their  huge clan that they don’t get to see for nine months.  Whatever the true motivations and feelings are,  these intrepid socialists gather in the hundreds, the thousands and even – in at least one documented case in Oklahoma – in the millions  – with the purpose of all sleeping in a few trees together!  It’s called roosting.  Why do they do this?  Primarily for safety say the experts.  During the long winter nights, they are especially vulnerable to nighttime predators like  Great-horned Owls.  Roosting in large groups gives them more protection.

Crow entering tree
Another crow flies in to pre-roosting site, February 4, 2018, Photo by B. Riverwoman

In the process of reading about crows, I also discovered that crows  were originally drawn to agricultural lands outside of cities.  But they were unwelcome guests –– driven off by guns, firecrackers and furious farmers who didn’t appreciate their fine brains.  So over time the crows  have congregated more and more in urban areas like ours – another reason that we see so many of them.  They are mostly ground foragers preferring open spaces with just enough nearby trees for cover.  They are never found in  densely vegetated areas like forests.  Being undiscriminating omnivores, they will eat just about anything – from wild plants and seeds to carrion and human garbage.  This is another reason we city dwellers see so many of them.  We have so much garbage lying around.

The one thing that I wasn’t able to find out from the online literature was more about their roosting.   Close to sundown, I got to witness first hand  large flocks of crows (about 250)   flying in from all directions and assembling on some sycamores and cottonwoods along the river. They never stopped emitting their strident chatter,  creating a huge, cacophonous racket that never stopped.   Some of them hopped into the river for a very splashy bath, others  got a drink of water, others gathered bedtime snacks along the sandbars and most of them settled into an already crowded tree for the night.  I assumed they had found their night time roosting spot and were settling in for the night. I seems I was wrong.

drinking crow
Crow getting a drink of water near pre-roosting site. February 4, 2018, photo by B. Riverwoman
crows - flock of 270
Crows bathing together in river north of Water St. Bridge, near pre-roosting site, anuary, 2018, photo by B. Riverwoman

The second time I watched the scene, I again saw them all settling into  the cottonwoods along the Benchlands.  But I hung around longer this time.  After about 30 minutes it slowly dawned on me that they were peeling off alone or in groups of 2 or 3 , leaving the tree I was photographing more and more empty – until it was entirely bare.  Now I saw dark shapes slipping silently downstream in the twilight, no longer a loud chorus of wildly chattering birds.

two crows flying
Crows leaving pre-roosting site, heading off downstream, February 4, 2018, Photo by B. Riverwoman

Were the sycamores that I had been watching  only a way station?   It suddenly made sense to me that the wily crows might not have wanted to advertise their actual sleeping place with so much drama.  It was as if they had chosen their first place as a site where they could  greet each other,  pass on messages of the day, bathe, snack, and maybe talk about where they would go next.  But perhaps haunted by memories of furious farmers with guns, or of Great Horned Owls (crows have prodigious memories), they understandably did not want to advertise where they actually planned to spend the night.   I tried to follow them.  I crossed the bridge, followed them downstream in the direction they were all going and peered out into the distance.  But no sounds and no flocks.  They had given me the slip!   I went home and started reading and discovered the term ‘pre-roosting site’.   Ah!  That was the concept I needed to understand what I had just seen.   I am now seriously on the trail of a final roosting site!  I’m wondering how many birds might be found there.  I wish I could tell them I carry only a camera and a loving heart, not a gun.  Nor do I want to eat them.  I’m a vegan.

While in pursuit of the departing crows I saw 10 CANADA GEESE AND 2 GREATER WHITE-FRONTED GEESE,  calmly nibbling away on the grassy lawns near the Duck Pond.  This was only my second sighting of the latter less common goose, bringing my total goose species to three this year – including the much rarer Snow Goose I wrote about several months ago.  The orange legs, white forehead shield and pinkish beak of the Greater White-fronted Goose give her quite a fanciful look, don’t you think?

Greater White-fronted Goose.jpg
Greater White-fronted Goose, February 4, 2018, grassy lawn near Duck Pond, photo by B. Riverwoman

Bad as the world can seem some days under the new Trump regime, there is still lots to crow about, isn’t there!  At least in the world of birds. Let’s keep cawing loudly about these wonderful birds on our river!

My best to all lovers of nature.

Barbara

 

 

 

 

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6 thoughts on “Where Are You Going, Crows?

  1. Hi, Good writing as always. I have Ravens over here on the east side, Merrill St and 14th. Here is the difference. Mk http://www.audubon.org/news/how-tell-raven-crow

    On Tue, Feb 6, 2018 at 6:59 PM, San Lorenzo River Mysteries wrote:

    > Barbara Riverwoman posted: “Hello Jane and All Other Bird Lovers, Lately > I’ve been stumped when people ask me ‘What’s with all the crows these > days?” Like me, they are astonished and mystified at the huge numbers of > these darksome creatures that sometimes, especially at sunset, se” >

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    1. Thanks so much, Michael. So happy you read our blog. There are always a few raven croaks among the overwhelming number of crow caws along the river. But not that many. I wonder why you have more ravens. Thanks for the great link.

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  2. Thank you for such a wonderful description of crow behavior. I know they get a bad rap for their predation on other bird’s chicks. I have read that studies show that the removal of crows from areas hardly affects the other birds. Cats are a much bigger problem.
    I like crows. They are songbirds too! Albeit less melodic than most.

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  3. Hi Kimberly, Thank you so much for being such a faithful reader of our blog. We’ve been meaning to walk the river together for quite a while. Let’s do it! Very interested in your comment on the effect of crows on other birds. Good news.

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  4. I don’t understand how roosting in a large flock lends protection to a crow. By yourself in some isolated tree I would think you would be less likely to be found. I understand in the case of schooling fish that being in large numbers makes it hard for a predator to track any one fish and thereby catch it. But crows in a tree are sitting…..crows.

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  5. Hi Michael,
    I looked for the source of this information but couldn’t find it. I know I read it in a pretty reliable source. I’ll keep looking and let you know. In the meantime here is more scientific info than anyone might want to know about crow roosting behavior. I wonder if Word Press will let me copy all this in a reply box Here goes… It is from Birds of North America, the summary of the most recent scientific research.

    Sleeping, Roosting, Sunbathing
    Sleeps with head held back (one side or other), bill tucked under scapular-feathers, or head drops forward, at times lower than perch. Sometimes sleeps while standing (during day); often legs bent, belly resting on perch (both day and night; Reaume 1985, CC).
    During nesting season, adults (Sullivan and Dinsmore 1992 , Caccamise et al. 1997), auxiliaries and nonhelping yearlings (CC), and recent fledglings (Knopf and Knopf 1983) roost on the territory. Breeding males sometimes leave territories and join local communal roosts (CC). After the breeding season, begin to gather in small, communal roosts; considerable individual variation in whether a crow roosts on its territory or in a distant communal roost, even from day to day. By mid-Apr in New Jersey, most stop going to distant roosts (Caccamise et al. 1997). Near Stillwater, OK, individuals in cooperative groups may sleep either in their territories or in communal roosts in fall and winter (CC). Gradually roosts get larger as more local crows and migrants join in, to reach maximum size by early to mid-winter. By late winter–early Mar, numbers decline as migrants depart and more residents remain on their territories.
    In morning, shortly before and after daybreak (Aldous 1944, Black 1941, Reaume 1985), leave roosts in small groups and fly in all directions leading to feeding grounds. Time from leaving feeding grounds to entering the roost in evening takes much longer than reverse process in morning (Black 1941, Stouffer and Caccamise 1991b, Caccamise et al. 1997). Starting 2–3 h before sunset, small groups of local crows gather in preroost sites, including trees, buildings, and on the ground (Hudson 1977). From there, fly along regular flight lines toward the roost but may stop at one or more additional preroost sites, where joined by other small groups. Preroost sites near Davis, CA, ranged from 200 m to several kilometers from each other, and were >1 km from the final roost (Moore and Switzer 1998). The closer to the final roost, the larger the groups become. Individuals arriving in groups settle independently of others in the group (Moore and Switzer 1998). Members of cooperatively breeding groups (see Breeding: cooperative breeding, below) usually leave the feeding area and the roost independently of each other and show no tendency to roost together (Caccamise et al. 1997). Individuals that fly high when coming to the roost often descend in a wild, tumbling flight, and ≥2 crows may chase each other in the process (Good 1952 , Reaume 1985). At some roosts, crows may gather on the ground nearby, where they feed, preen, and scan the surroundings, and from which they fly into the roost (Black 1941, Moore and Switzer 1998). Crows captured and radio-tagged on a farm in New Jersey from mid-Nov to end of Mar represented 2 types of birds: residents and vagrants (of migrant origin). Although both types roosted together, only residents returned daily to their own feeding territories (Stouffer and Caccamise 1991b). Banded crows in Iowa flew up to 20 km to a communal roost but returned each day to their own territory to feed (Schaefer 1983). Both urban (Ithaca, NY) and rural (surrounding areas) crows left their territories to enter winter roosts; could be found together in roosts and could be present in either urban or rural roosts (McGowan 2001a).
    Compared to randomly selected nonroost trees (n = 62) in Woodland, CA, roost trees (n = 87) had greater height (18 m ± 0.6 SE vs. 13.1 m ± 0.5 SE), diameter at breast height (62.3 cm ± 2.2 SE vs. 45.9 cm ± 2.6 SE), crown diameter (12.7 m ± 0.3 SE vs. 10.0 m ± 0.4 SE), and crown volume (854.1 m3 ± 64.0 SE vs. 421.9 m3 ± 54.8 SE). A greater proportion of roost trees than randomly selected nonroost trees were located over pavement in commercial areas than in residential areas, and they were subjected to more traffic. Ambient light levels and interior canopy temperatures during winter were higher in roost trees than in nonroost trees. Crows tended to switch from deciduous trees in residential areas in summer to evergreen trees in commercial areas during winter (Gorenzel and Salmon 1995 ).
    The same roosting sites may be used for many years (Emlen Emlen 1938b , Emlen 1940b ; Black 1941). In a survey of roosts in New York State, 6 had been used ≥40 yr, 1 >125 yr (Emlen 1938b). Total number of birds in roosts varies from a few hundred to >500,000 (Gorenzel and Salmon 1992), to >2,000,000 (Iams 1972). Very large roosts generally occur in regions with abundant food, where resident populations are augmented by northern migrants, such as in Oklahoma (Good 1952). From such roosts, crows range 24–56 km (Emlen 1938b), 24–32 km (Black 1941), 13–19 km (Aldous 1944 ), 40–48, and as much as 80 km (Good 1952) to feed; mean distance in Iowa 7.5 km ± 4.6 SD (range 1.5–24.0, n = 7 roosts; Schaefer 1983), and in Ontario 25 km (Quiring and Timmins 1988), and at least 34 km (Reaume 1985). Mean foraging area around roosts 110.8 km2 ± 63.2 SD (range 25.9–165.9, n = 7 roosts); area positively related to size of roost (Schaefer 1983).
    In St. Catherines, ON, crows began arriving at the final roost 30–40 min before sunset in fall, and entered the roost from 10 min before and after sunset (Knapton and Maturi 1984), but there are several reports of crows entering the final roost up to 44 min after sun-set (Hudson 1977, Knapton and Maturi 1984); probably the result of city lights (NAMV). In an Ohio study, crows began to enter the roost at a light intensity of about 500 foot-candle and at 15 foot-candle all birds were in the roost (Haase 1963 ). Relative to sunset, 50% of the crows had entered the roost between 7.8–17.3 min before sunset, 75% between 0.2–10.7 min, and 100% between 6.7–10.1 min after sunset, the variation being mainly due to wind velocity.
    High wind velocity and cloud cover hastens roosting (Haase 1963). Densities in roost: 5.4 crows/m2 (Aldous 1944), 3.7/m2 (Gorenzel and Salmon 1992), 0.7–1.1/m2 (Hicks 1979) of ground surface. In Davis and Woodland, CA (and elsewhere), uses deciduous trees (58% of 198 individual trees identified; alder [Alnus sp.], sycamore [Platanus sp.], mulberry [Morussp.], oak, elm [Ulmus sp.]), olives [Olea sp.]), and evergreen trees (42%; pines [Pinus sp.], redwood [Sequoia sp.], and deodara cedar [Cedrus deodara]). Continued to roost in deciduous trees after leaf-fall (Gorenzel and Salmon 1992). In Oklahoma, roosted mainly in scrub oak (species not indicated) thickets on hillsides protected from the wind (Aldous 1944); in New Jersey, 3- to 8-m-tall red alder (Alnus rubra) and white spruce (Picea glauca ; Stouffer and Caccamise 1991b). Low trees seem to be selected more often than mature timber (Black 1941).
    In sunbathing posture, body flattened against ground or branch, wings and tail feathers spread, as in anting posture (see Behavior: self-maintenance [anting], above; CC). Raises head-feathers, tilts head back and sideways, and holds this position for several minutes as if in a trance; opens and closes nictitating membrane while holding bill open and pointed upward (Kilham 1989, CC).
    Daily Time Budget

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