Of Falcons and Hawks: Rules for Birds of Prey

Birders are well-aware of the recent change in their checklists, which annoyingly relocates the falcons away from hawks, eagles, and other diurnal birds of prey, and puts them deep among the little birds– just before flycatchers. Here is the dramatic rationale behind it.

Collared Forest-falcon No Goshawk

It used to be that there were a few obvious examples of convergent evolution in the bird world– like meadowlarks and longclaws— and then a bunch of lesser known examples for which this blog is dedicated, in part, to illustrating. However, recent DNA analysis has blown the lid off this idea. It now seems that convergent evolution is practically the norm rather than the exception– that various groups of species once thought closely related (and put adjacent to each other in field guides) are not related after all– that they each evolved, convergently but separately from each other, to serve a similar role in the ecosystem on different continents, though many have since spread out over each other. Near the top of this list of DNA-discovered examples of convergent evolution is the conclusion that Falconiformes (falcons and caracaras) and Accipitriformes (which includes eagles, hawks– both Buteos and Accipiters, kites, harriers, and Old World vultures) are not related to each other. Well, if you go back millions of years they are related in the same way that songbirds and owls are related (which is very very distantly).

Essentially, the story is this. After the breakup of Gondwana over 100 million years ago into Africa, Australia, and South America, hawks evolved in Africa and falcons evolved in South America independently of each other. It was if each place needed a diurnal raptor for their ecosystem, and each got one. Actually, each got a bunch of them– and the parallels include many details and sub-examples at the species level.  (Thanks to their ability to fly, both hawks and falcons have since spread around the world.)

Pangaea timeline maps2From Ericson, P.G.P. 2012. Evolution of terrestrial birds in three continents: biogeography and parallel radiations. Journal of Biogeography 39, 813–824:

It can be postulated that after the break-up of Gondwana in the Cretaceous the terrestrial avifaunas of Africa, South America and Australia were more or less isolated from each other for many millions of years. In each continent different bird groups responded to the local conditions by evolving a range of ecological adaptations. Because of a general similarity in major habitat types between the continents, several specializations evolved in parallel in different phylogenetic lineages. This becomes evident when comparing the ecological adaptations of bird groups in Afroaves with those in Australavis…. Another example of convergence
in ecological adaptations is the parallel evolution of diurnal predators in the two clades, Accipitriformes in Afroaves and Falconiformes in Australavis [which includes species that evolved in South America].

barren forest falcon collared sparrowhawkThus, any similarities between hawks and falcons is due to convergent evolution.  Let’s list some of them:

  • Shape — similar proportions, often with a longish tail, rounded to pointed wings for either maneuvering or hovering.
  • Bare parts — sharp, hooked bills, usually with a yellow cere; large eyes with usually yellow irides– and excellent vision; often yellowish legs with sharp talons for grasping prey.
  • Size — generally ranging from a little larger than a robin to larger than a raven, with most about 10″ to 15″ long.
  • Plumage — features creamy white, blue-gray, and brown, often with a touch of orange-red; usually dark above, pale below (often finely barred or with a dark belly band), barring on wings and tail, with dark cap, dark around the auriculars or elsewhere between the malar and eyeline; pale throat.
  • Habits — being predators, most are fairly solitary; most will sit still for long periods of time, watching for potential prey, and many will soar in circles; many dive or chase prey at high speeds.
  • Calls — most have piercing high-pitched or raucous calls, often repetitive; they do not have songs.

bat falcon bat hawkThere are many species-specific parallels to be drawn; photos of a few comparisons are shown here. The last pairing, the Bat Falcon and the Bat Hawk, is noteworthy because they are each the “bat specialists” of the two groups, feeding primarily on bats at dawn and dusk.

 

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Does Convergence Imply God?

In the words of Job, in one of the oldest pieces of literature in the world, I now speak of wonders beyond my comprehension.

earth

In the world of Stephen Jay Gould, life evolves unpredictably. Creatures adapt to ever changing situations in whatever ways are most successful.  If an asteroid hits the earth and dramatically changes the climate, the trajectory of the world is likewise changed, with species adapting and evolving as conditions warrant.  It is unpredictable and subject to random chance.  If we could rewind the clock back to the beginning and start over, we would get a completely different world.  In this purely materialist, random, and accidental world, there is little room for God.  Certainly, this worldview seems to conflict with the concept of a relational God that seeks some interaction with humans (or other species for that matter).  This is the predominant worldview in the post-Christian modern world.

In the world of Simon Conway Morris, evolution follows far more predictable patterns.  Creatures still evolve and adapt to changing conditions, but they do so in predictable ways, repeating patterns over and over again.  Different unrelated species, faced with similar conditions, converge upon the same solution to an astonishing degree of detail (which is the main focus of this blog). In this world, if an asteroid hits the earth and dramatically changes the climate, the trajectory of the world does not change significantly.  Sure, creatures die and others evolve, but the asteroid is merely a bump in the road of an inevitable journey. Eventually, there will be birds (or flying mammals, or insects, or something else) that look like meadowlarks and longclaws and live in weedy fields, possibly even singing from fence posts put there by humans (or some other species).

Many merge Gould’s and Morris’s worlds, pointing out that they are not necessarily in conflict. Species converge upon similar patterns because they work. These are the solutions which species evolve into repeatedly.  It is both random and predictable.  Gould might shrug and say, so what, there is convergence. Morris might jump up and point at the rewinding clock, saying, see, the world would not turn out differently.

If every pasture must have its meadowlark, every wetland its black bird with red shoulders, and every open plain its banded plover or wagtail, then the biological world is a predictable place.  There is order. Evolution has directionality—even inevitability.  That is, it may be inevitable that a species like a meadowlark evolves to fill that ecological space.  This implies that the unique role of humans, with intelligence and extensive developed societies, may be part of that inevitability. Either that or we dismiss humans to a one-off event, or perhaps we interpret humans as a replacement for elephants, fulfilling an inevitable ecological niche. But perhaps humans, or a dominant species with similar traits, domesticating animals and managing the landscape, are in fact inevitable.  Note we need not be primates.  We could have evolved as human-like versions of marsupials or even dinosaurs (were in not for one particularly large asteroid).

When it comes to imagining God, anything, of course, is possible.  Gould’s random accidental world may have a God, or Morris’s well-ordered universe with convergence and inevitability may just be the way of things without a God. If, however, we define God as specifically interested in a relationship with humans (or any other part of creation), then we can say that Gould’s random world is potentially not consistent with such a God (unless that God were willing to relate to whatever random life forms evolved, which I suppose is possible).  At the very least we can say this:  If the biological world has convergence, directionality, predictability, and inevitability, a relational God may exist. Without those things, any God that may exist seems far removed from life on Earth.  Thus, a world with convergence and predictability, where meadowlarks and humans are inevitable, is at least consistent with the concept of a relational God.  It is certainly not proof of such a God, but it does rule out the random accidental world where everything is chance and God seems irrelevant.

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Of Mousebirds and Bushtits: Rules for Gregarious Gray Family Groups

bushtits

A family group of Bushtits clamber around a suet feeder in North America.

This is one of those easy comparisons that any birder with experience in western North America and sub-Saharan Africa can make. Growing up in California, I was quite familiar with Bushtits. Little gray birds with long tails and stubby bills, they move from bush to bush in open country in family groups of ten to thirty individuals, often with total disregard for a human standing nearby. Their gregarious habits, clambering around vines and vegetation, hanging upside down,  chattering little “sip” notes to each other, are conspicuous. They are a party unto themselves.

mousebirds

A family group of Mousebirds sleep together on a branch in Africa.

So I was astonished to be walking across the grounds of Bunda College in Malawi when a group of over-sized Bushtits came my way. Though larger than our Bushtits, and with crests, their mouse gray plumage and group behavior, bounding bird after bird from bush to bush calling to each other, was identical to the Bushtits back home. I was astonished at the similarity.

Interestingly, both locate their nests near danger to ward off predators– Bushtits commonly nest above human walking paths, while Mousebirds choose to locate near wasp nests.

While these videos don’t show the characteristic way the flocks move from bush to bush, they do illustrate their communal behavior.  Compare these Bushtits coming to water

with these Mousebirds at some fruit:

Bushtits are from the order Passeriformes (songbirds).  Their family includes ten other “bushtits” in Eurasia, such as the Long-tailed Tit.  They evolved rather recently, about 14 million years ago. Mousebirds, on the other hand, aren’t even Passerines; they are from the order Coliiformes, one of the most ancient lineages of Aves (Birds).  Mousebirds and Bushtits last had a common ancestor over 65 million years ago, and yet have evolved to fill some peculiar niche in certain semi-open habitats in different places around the world. Somehow this behavior fits into the great ecological jigsaw puzzle, and they each, separately, evolved to fill that niche.

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Of Elephants and Sperm Whales: Parallel Societies

Swimming elephants

If convergent evolution was the universal norm, we might expect to travel in space and find another planet with a complex ecosystem and species that mirror those found on earth.  Perhaps, if the planet had solid land, there would be plant life with similar functions and ecological roles as on earth, and likewise, similar communities of animal life.  There would not be elephants exactly, but there would be something large that serves a similar ecological role.  Based on some of the convergent examples already mentioned in this blog, this elephant-like beast might even have a similar appearance and similar life history characteristics.  If the planet were water, we might find similarities to earth as well—perhaps some schooling fish-like species, larger predators, bottom-dwellers, broadcast spawners, etc.

elephant1Because earth has both land and sea, we can look for parallels in the communities of species that live in each of them, almost like looking at two different planets.  In doing so, we find remarkable parallels between two of the very largest species that inhabit these worlds:  elephants and sperm whales.

  • They are both very large, among the largest land and sea animals.
  • They each have the largest brain of any land or sea animal.
  • They both range widely, eat a varied diet, and consume so much food that they actually impact the habitat around them. Elephants are said to impact their landscape more than any other land animal except humans; sperm whales consume 100 million metric tons of food each year (equal to all marine fish consumption by humans), despite their reduced numbers from historic whaling.
  • Both species are long-lived and slow reproducing. They both:
    • mature in their teens
    • live about 60 years
    • almost always give birth to single calves at about 5-yr intervals
    • see female productivity decline after age 40; after that, females serve the role of clan leaders in highly structured female societies.spermwhale1
  • Both elephants and sperm whales organize socially around a matrilineal family of about ten animals, all related females and their offspring, headed by a matriarch.
  • Females remain in their family groups their entire lives, during which they move, feed, drink, and rest in unison together. The call in synchrony and stop to listen together. They often rub against each other, or caress each other with their trunks, jaws, or flippers (as the case may be).
  • Both species engage in communal calf care. Calves nurse from other females in addition to their mother, although they may not actually obtain milk from them.  The family groups create defensive formations to protect calves from threats.  They come to the aid of injured family members. spermwhale2
  • In both species, family groups spend some of their time associating with one to three other family groups.
  • Both elephants and sperm whales communicate at frequencies below the range of human hearing, across distances of 4 km for elephants, 8 km for sperm whales (taking advantage of the way sound waves move in water).
  • In both species, the adult males rove independently, seeking out females only when breeding. They form loose bachelor groups when not breeding.  Males of both species are capable of breeding in their teens, but generally do not do so until their mid-twenties.  Non-breeding adult males tend to live distant from the female family groups.  (In sperm whales, the family groups congregate in the tropics, while the males may move toward the poles.)Elephants Family
  • Finally, both species have been subject to human depredation, and both populations recover slowly due to their very low reproductive rates. For both species, it was assumed that there were many “surplus males” in their population, and that these could be harvested without impacting the population’s annual reproduction.  In both cases, however, this has been shown to be wrong; the number of newborn calves is closely tied to the number of males in the population.

For the space traveler coming to earth, they would undoubtedly notice a third dominant species that is impacting the planet (including elephants and sperm whales) and shares many of these same demographic and life history characteristics:  humans.  (Note that matrilineal societies used to predominate among many ethnic groups in the Americans, Asia, and Africa.)

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Of Hummingbirds and Sunbirds: Rules for Jewels

hummingbirds

Clockwise from upper left:  Tufted Coquette, Green Thorntail, Gould’s Jewelfront, Green Violetear, Ruby-Topaz Hummingbird, Fiery-throated Hummingbird, Allen’s Hummingbird (center)

Early European explorers were amazed by the hummingbirds of the Americas, with their dazzling colors and ability to hover and even fly backwards.  Across Africa, Asia, and Australia, however, hummingbirds have a near-equal.  While not quite able to maneuver as much (though most can hover), sunbirds are just as dazzling.  Both species groups have iridescent feathers that shine in sunlight at just the right angle, but otherwise may appear rather dark and dull.  And both, of course, zoom around flowers, feeding on nectar and small insects.

The two groups are separated by the Atlantic and Pacific Oceans– and 80 million years. Sunbirds are Passeriformes; hummingbirds are not.

sunbirds

Clockwise from upper left:  Double-collared Sunbird, South Africa; Variable Sunbird, Ethiopia; Malachite Sunbird, Tanzania; Crimson Sunbird, Singapore; Gould’s Sunbird, China; Purple Sunbird, India; Green-tailed Sunbird, Thailand (center)

 

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Of Wagtails, Wheatears, and Plovers: Rules for Open Country

blackwhite5

White-browed Wagtail, India; Banded Lapwing, Australia; African Pied Wagtail, Africa; Pied Plover, South America

As we move from conspicuous birds of wetlands to more open country, such as desert and short grass habitats, other rules for plumage and behavior prevail.  Many of the birds maintain conspicuous patterns, but revert to more bold black-and-white patterns.  Some include the classic white eye-stripe and black V or U across the breast.  Regardless, the patterns are bold and large, not fine and intricate.  There are no flanks streaks or fine spots.  These birds are painted with a wide brush.

Nearly all are found on the ground, or near to it.  These birds also have a tendency to stop and look from a rather upright alert posture.  These patterns and behaviors extend across a wide range of species and continents.  Note that plovers and wagtails last had a common ancestor 80 million years ago.

blackwhite2

Pied Wagtail, Eurasia; Pied Water Tyrant, South America; Long-toed Lapwing, Africa

Some have more pied appearances, with white faces framed with black on the nape and elsewhere on the body.  These birds are frequent near water.

blackwhite1

Hooded Wheatear, Middle East; Long-tailed Tyrant, South America; Blacksmith Plover, Africa

Others are the opposite, with white caps and black faces.  The tyrant is from the forest, but in relatively open contexts within that habitat.

 

 

 

 

In very open country, some have black underparts, unusual in birds.  Some feature white primarily on the side of the face (or the wing), while their underparts are black and upperparts gray or brown.  In some, pale bills provide additional contrast to largely black heads.

blackwhite4b

Lark Bunting, North America; Chestnut-collared Longspur, North America; Chestnut-backed Sparrow Lark, Africa

blackwhite3

Black-bellied Plover, Arctic breeder but found worldwide on coasts; Black-bellied Bustard, Africa

Another variation is a wash of black down the front of the neck to the belly, framed with white edges, often with the white bulging prominent at the sides of the breast.  The upperparts are spangled gold or silver.  These birds occur in short grasses.

blackwhite4a

Spur-winged Lapwing, Africa; Northern Black Korhaan, Africa

blackwhite7

Hodgson’s Bushchat, Asia; Lesser Sand Plover, Asia

 

In some contexts, rusty red or orange is added to the mix, often across the breast or on the head (see the Chestnut-collared Longspur above).  In very arid or open environments, the birds are pale white below, gray above, with just a touch of black (such as a dark eye-line or primaries), and a rusty cap.

 

 

 

 

 

 

 

 

 

blackwhite6

Red-capped Plover, Australia; Rufous-naped Ground Tyrant, South America

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Contingency and Convergence: Are the Gods Plagiarists?

There are two concepts regarding the process of evolution: contingency and convergence.

Contingency

This theory holds that species evolve, due to natural selection, randomly according to whichever new adaptation is useful. The present is contingent on random events that occurred in the past (such as an asteroid hitting the earth). There is no directionality toward more advanced organisms; there is no predictability; anything is possible. If one were to re-wind the clock and start Life over at Year Zero, the world evolving from that would look very different from our world today. There would be no mammals, fish, plants, or anything necessarily resembling them. As Stephen Jay Gould states, “We are the accidental result of an unplanned process …. The fragile result of an enormous concatenation of improbabilities, not the predictable product of any definite process.”

Convergence

This theory agrees that natural selection is the motor that drives evolution, but that it is largely influenced by circumstances that cause separate evolutionary lineages to arrive at the same conclusion. Circumstances may include gravity, water, climate, and the general environment/habitat (of co-evolving plants). For example, both ducks and the platypus evolved duck bills, a very specific adaptation for a similar ecological niche. Both Red-winged Blackbirds and Fan-tailed Widowbirds evolved to have males with black bodies and red shoulders (with white borders) and sing from reeds in marshes, while the females are streaked brown.  They have converged to become similar species, although they are quite unrelated.  In this way, many species independently evolve in predictable ways that are replicated in time and space around the world. They converge over time and look like each other.  Moreover, directionality is also evident. Species evolve from simple to complex, from blob to human. (Some have taken the theological step that convergence and directionality imply universal rules which suggest the work of a Divine Hand.  That discussion is beyond the scope of this blog– for now at least.) If one were to re-wind the clock and start over in Year Zero, we’d still end up with a world pretty similar to the one we have now, with a similar mix of species fulfilling similar functions. As Simon Conway Morris states, “Although there may be a billion potential pathways for evolution to follow from the Cambrian explosion, in fact the real range of possibilities and hence expected end results appear to be much more restricted.”  That is, there are only so many options and species will fit into those options.  Anything is not possible.

There are actually a range of theories that combine aspects of contingency and convergence, in differing amounts.

whitebrows

Left to right: White-browed Conebill, South America; Slaty-backed Chat-Tyrant, South America; Slaty-backed Hemispingus, South America; Snowy-browed Flycatcher, Asia; Indian Blue Robin, Asia; White-browed Woodswallow, Australia

If only contingency was the case, birds would evolve in random ways, developing ever more unpredictable and bizarre shapes, sizes, and colors. Bird identification would be easy, as they’d all be so different (except right when closely related species are separating from each other). If convergence was the rule, we’d expect the same patterns to recur time and time again. Bird plumages would be limited to certain patterns and colors, and probably correlated with certain behaviors, habitat preferences, and ecological functions. There would be birds from completely different families, very distantly related to each other and on different continents, which might evolve looking very similar to each other. As my son puts it, the gods of evolution would look like plagiarists.  I believe this is clearly the case, for reasons that are not always easy to understand.  For example, the six Passerines above, all inhabitants of woodsy areas but only very distantly related, have solid blue-gray upperparts, reddish underparts, and white eyebrows.  It’s not clear what purpose this serves, but clearly it’s a pattern they have all converged on.

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