Does wisdom perhaps appear on the earth as a raven which is inspired by the smell of carrion?
—Friedrich Nietzsche


Developmental Differences Correlate with Relative Brain Size in Birds

A long developmental period before juveniles become nutritionally independent from their parents has been thought of as one of the hallmarks of intelligence in apes; it is known that corvids and parrots have this extended period as well (Emery 2006).

Iwaniuk & Nelson (2003)
has applied rigorous statistical and phylogenetic tests to compare developmental mode and length of the developmental period with relative brain size in 1400 species of birds. Across all of the species tested, there were significant relationships between relative brain size and each of the following developmental traits: incubation period, age of fledging, duration of post-fledging parental care, and total period of parental care. They found a positive correlation between delayed maturation and relative brain size for the birds examined.

Neophilia in Juvenile Foraging: A Critical Period for Food-finding

As young animals learn to forage, they experiment with many potential foods and narrow their preferences in light of their experience. The range of foods available in an animal's habitat determines whether animals are generalist feeders or specialists. Animals that are highly specialized in diet have a rigidly determined preference for specific stimuli during this period of exploration, whereas more generalized feeders do not. In many small passerines, narrow ecological specificity is associated with neophobia (Greenberg 1990). Corvids (particularly crows and ravens), however, tend not to be restricted to a specific ecological setting and eat a diverse, opportunistic diet.

Bernd Heinrich (1995) studied neophilia in four juvenile ravens (just fledged) by exposing them to a natural area for 10 trials and recording the number and kind of objects contacted by their bills to establish background. For the next six exposures, he provided novel inedible items that closely resembled the background items (including seeds, leaves of different types, birch and spruce cones, flower buds). None of these 'natural control' items was contacted more than 16 times on the first of these trials. His next 12 trials were experimental, sometimes including edible or potentially edible novel items. The first three of these 18 trials are documented in the table to the lower right of your screen (taken from Heinrich 1995). Initial preference for the novel items was generally thousands of times above background, and each novel inedible item was ignored by the birds upon their second or third exposure. The high tendency to single out novel items to the exclusion of old ones was observed in each successive trial. He then examined directly whether this behavior aids in food finding, and found that the birds never missed any potentially edible item he put out, even with "highly cryptic objects." His results indicated that neophilia allowed young birds to explore so thoroughly that virtually all novel food items should be found. One year later, he again examined whether the birds were attracted to novel items in the same area. On two occasions, he presented the four birds with five novel items each time. One of the male birds gave alarm calls each time, and the other birds showed no observable reaction.

Heinrich demonstrated that ravens gain exposure to potential food items through the intense curiosity with which they sample their environment during their youth, contacting most everything they encounter. Rapid learning accompanies these exposures and refines future focus to relevant stimuli (like food). They learn quickly to distinguish food from non-food, and selectively screen out the non-rewarding items. The shift from neophilia to neophobia with age (Heinrich 1988) suggests that this curious period in the birds early life has important implications for foraging in later life.


Though confusing at first glance, this table is very informative. It depicts object choice during six half-hour observation periods: when highly conspicuous inedible objects (winterberries) were present (15 June), when another kind of conspicuous inedible object (carrots) plus conspicuous edible objects (blueberries) were added
(16 June), when the inedible objects remained but nothing new was added (17 June), when new cryptic objects were added (18 June), when new showy and cryptic objects were added together (including cigarette butts, note: not blueberries) (21 June), and when with most of the previously-added showy inedible objects remaining, previously contacted edible objects (blueberries) were added (26 June; disregard the discoloration at the top of the bar--the only two objects contacted were blueberries and background). Numbers over bars refer to total number of objects contacted. All material taken from Heinrich (1995).


Piagetian Measures of Object Permanence

During early development, human children pass through several distinct stages marked by their relative understanding of their physical and social environment (Piaget 1952).

In children, object permanence (the understanding that an object still exists when it can no longer in view) develops in distinct stages during development: from tracking the movement of visible objects generally (Stage 2) and tracking partially hidden objects (Stage 3) to forming representations of fully hidden objects (Stage 4) and representing the visible (Stage 5) and invisible (Stage 6) displacement of hidden objects. Object permanence would appear to be an important ability for many animals to have, especially those who cache food or rely on predation. Food-caching magpies (Pica pica) display Piagetian Stage 4 object permanence around the age at which they begin recovering cached food (44 days old), and also achieved Stages 5 (65–107 days old) and 6 (Pollok et al. 2000).

This website was created by Nathaniel Raley for Suzy Renn's Animal Behavior course (BIO 342) at Reed College, Fall 2010