Corvidae · Kindred Archive IV
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The Kindred Archive · Volume IV · Corvidae

A Field Guide to the Cunning

Sixteen crows, ravens, jays and magpies — sorted by clade, habitat and fortune, with comparative plates and working notes on what the family actually does.

  • Sixteen species
  • Four clades
  • Five habitats
  • Revised 2024
Wing formula, Corvus corax. The ten primaries drawn to relative length, P1 at the left. The fourth is the longest; the outermost is barely half of it. Every corvid in this index can be told from its neighbours by this row of numbers alone.
I

The Index

One facet from each axis
Clade
Habitat
Status

  • Common Raven Corvus corax

    Holarctic54–67 cmLeast concern

    Field notes

    The largest passerine in the northern hemisphere, and the one most given to play: birds have been watched sliding down snow-covered roofs and passing sticks to one another in flight. Cache protection is a strategy — a raven seen while hiding food will often move it once the observer looks away.

  • Carrion Crow Corvus corone

    Western Palearctic44–51 cmLeast concern

    Field notes

    Solitary and territorial where it overlaps with the Rook, and a patient reader of road surfaces. Where its range meets the Hooded Crow's — a band running through Scotland, Denmark and the Alps — the two interbreed freely, and the argument about whether they are one species or two is not over.

  • Hooded Crow Corvus cornix

    Northern Europe44–51 cmLeast concern

    Field notes

    The grey-and-black crow of the north-east, common in cities from Oslo to Istanbul. It is as bold a user of human rubbish as anything in Europe, and it will follow a plough or a collection truck for the length of a field.

  • Rook Corvus frugilegus

    Eurasia41–49 cmLeast concern

    Field notes

    A colonial crow with a bare, chalky face patch in adults — the only corvid whose skull shows through its plumage. Rooks nest in rookeries of up to a thousand pairs, and will drop stones into a tube of water to reach a floating reward, which is what most people know as Aesop's fable.

  • Western Jackdaw Coloeus monedula

    Europe, W Asia34–39 cmLeast concern

    Field notes

    The smallest of the crows, with a pale, almost white iris that gives it a permanently startled expression. Jackdaws pair for life, defend a cavity rather than a territory, and still nest on sea cliffs and quarry faces when a chimney is not available.

  • New Caledonian Crow Corvus moneduloides

    New Caledonia40 cmLeast concern

    Field notes

    The only bird known to make a hook by biting a stick into shape, and the only one known to cut a tool from a leaf with a sequence of stepped cuts. Young birds inherit the designs of their community: pandanus tools made on one side of the island differ measurably from those made on the other.

  • Mariana Crow Corvus kubaryi

    Guam & Rota38 cmCritically endangered

    Field notes

    Once widespread on Guam, it vanished from the island after the brown tree snake arrived in the 1940s, and now hangs on in the limestone forest of neighbouring Rota — a few hundred birds in all, nesting in the few tall trees that remain.

  • Hawaiian Crow Corvus hawaiiensis

    Hawaiʻi Island48–50 cmExtinct in the wild

    Field notes

    Extinct in the wild since 2002, and the corvid with the most fruit in its diet. Captive-bred birds have been released into the forest of Hawaiʻi Island since 2017; the pioneers have struggled with a predator they no longer recognise, and with fruit they no longer know how to find.

  • Eurasian Magpie Pica pica

    Eurasia44–46 cmLeast concern

    Field notes

    The only bird reported to have passed the mirror mark test — a claim published in 2008 and argued over ever since. Its nest is a dome of sticks with an entrance at the side, roofed to keep out the other magpies that would otherwise take it over.

  • Black-billed Magpie Pica hudsonia

    Western N America45–60 cmLeast concern

    Field notes

    The American counterpart, separated from the Eurasian bird by the whole of Asia and now treated as a species in its own right. It follows cattle and bison for the insects their feet turn up, and will pick parasites from the back of a standing horse.

  • Azure-winged Magpie Cyanopica cyanus

    Iberia & E Asia34–37 cmLeast concern

    Field notes

    One of the strangest ranges in ornithology: a population in Iberia and another several thousand kilometres east in China, Korea and Japan, with nothing in between. The Iberian birds live in cork-oak savanna, the Asian ones in pine forest, and no bird crosses the gap.

  • Eurasian Jay Garrulus glandarius

    Palearctic32–35 cmLeast concern

    Field notes

    The woodland hoarder. An autumn jay may bury several thousand acorns, carrying a handful at a time in an expandable pouch under the tongue, and it recovers only a fraction of them. A good deal of the oak woods of Europe were, in a real sense, planted by jays.

  • Canada Jay Perisoreus canadensis

    Boreal N America25–33 cmLeast concern

    Field notes

    It nests in February, on a bowl of twigs and spruce resin, when the temperature may be thirty below — the only passerine in North America to breed in deep winter. Food cached the previous autumn, stuck to bark with sticky saliva, carries the pair and its brood through.

  • Blue Jay Cyanocitta cristata

    Eastern N America25–30 cmLeast concern

    Field notes

    A loud, handsome bird that spends much of the autumn quietly moving acorns south. It mimics the calls of Cooper's and Red-shouldered Hawks well enough to empty a bird table, and caches thousands of nuts in a season — another deliberate planter of oak.

  • Steller's Jay Cyanocitta stelleri

    Western N America30–34 cmLeast concern

    Field notes

    Named for the naturalist who collected the first specimens during Bering's expedition of 1741, and a bird that must keep track of a season's worth of caches under a metre of mountain snow. It will also imitate a Red-tailed Hawk on its way into a campsite.

  • Florida Scrub-Jay Aphelocoma coerulescens

    Florida25–28 cmVulnerable

    Field notes

    A bird that requires fire. It nests only in low, open Florida scrub, and fire suppression has closed the canopy over most of it. The few thousand birds that remain live in family groups in which young adults stay on to help raise the next brood.

Showing of 16 species in view

II

Plates

Three comparative figures
Raven Rook Magpie
Plate I — Wing formula. The ten primaries of three species, P1 at the top of each block. The Raven's fourth primary is the longest and the outer two are short; the Magpie's wing is stubbier and rounder, as befits a bird that flies in short bursts between hedges.
Wedge Squared Graduated
Plate II — Tail geometry. Three answers to the same problem. The Raven's tail runs to a point; the Carrion Crow's ends square; the Magpie carries a graduated tail almost as long again as its body, and uses it as a rudder in flight and a counterweight on a branch.
Straight Hooked Stepped
Plate III — Tool kit. The New Caledonian Crow's three manufactures: a plain probe for grubs, a stick bitten into a hook for lifting larvae out of a hole, and a pandanus leaf cut along a series of steps and used to rake insects from crevices.
III

Field notes

On caching, theft and tools

Corvidae is not a large family — around 135 species, a little over one per cent of the birds — but no other family has been so thoroughly credited with thinking. What follows is an attempt to sort the evidence from the story: to keep what corvids are shown to do, and to put down what people find it satisfying to believe they do.

Start with the hiding. Almost every corvid caches food. A Canada Jay presses seeds into bark with sticky saliva in September; a jackdaw buries a crust in a lawn; a Florida Scrub-Jay stashes an acorn a few metres from where it found it. The habit is what forced the machinery. A bird that hides three thousand items must remember, months later, where each one is — and the memory that results is spatial, precise and indifferent to the passing of seasons.1

The second fact is that caches are stolen. Where corvids live close together they watch one another constantly, and being seen changes what a bird does next: ravens in particular will move a cache once the watcher's attention has moved on. The behaviour is usually described as deception, but counter-measure is the safer word. What has been demonstrated is the move; whether the bird holds anything like a belief about the watcher's mind has not been demonstrated at all.2

The birds that read us most closely are the ones that survive us best. The ones that never had a reason to are running out of forest.

The third fact is that the family makes tools — narrowly, but unambiguously. New Caledonian Crows bite hooks into the ends of sticks, and cut a second kind of tool from pandanus leaf along a series of stepped incisions. What is more striking than the tools is the variation: designs differ measurably between crow communities within sight of one another, which implies learning of some kind — imitation, teaching, or both.3

Corvids have done well out of people. Rooks followed the plough; jackdaws took to chimneys; magpies took to the verges of every road in Europe. The species in this index that have not done well are both island birds that never had a reason to fear a mammal: the Mariana Crow, which lost Guam to a snake that arrived in the 1940s, and the ʻAlalā of Hawaiʻi, extinct in the wild since 2002 and surviving in aviaries and a handful of hopeful release sites.

Measurements

Adult measurements, means of published ranges.
SpeciesMass (g)Wingspan (cm)
Common Raven690–1,600116–130
Carrion Crow300–60084–100
Eurasian Magpie180–27052–60
Blue Jay65–11034–43
Florida Scrub-Jay66–8733–36

Terms

Cache
A food store hidden from view and recovered later, often months later and often under snow.
Counter-measure
A behaviour that reduces the chance of a cache being stolen, such as re-hiding food after being watched.
Cooperative breeding
A system in which grown offspring stay with their parents and help raise the next brood.
Wing formula
The relative lengths of the ten primaries, used to tell apart species that look alike in the field.
IV

Colophon

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Sources for the notes above: Heinrich, Ravens in Winter; Hunt & Gray on New Caledonian crow tool manufacture; Prior and colleagues on the magpie mark test. Measurements after standard regional handbooks, rounded to the nearest gram.