Bird Classification & Diversity

Question 1

Approximately how many bird species are there in the world?

Answer 1

There are about 10,000 bird species globally.

Question 2

Despite their incredible diversity, all living birds descended from a common avian ancestor how many years ago?

Answer 2

All birds evolved from a common ancestor that lived approximately 130 million years ago.

Question 3

How do scientists learn about ancient birds and their relationships with each other and other dinosaurs?

Answer 3

We learn about ancient birds through ongoing fossil discoveries.

Question 4

What is systematics?

Answer 4

Systematics is the classification of organisms into a hierarchy of taxonomic levels.

Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Question 5

What is phylogenesis?

Answer 5

Phylogenesis is the evolutionary development and diversification of organisms (or of a particular feature of an organism).

Question 6

What is a phylogenetic tree (or phylogeny)?

Answer 6

A phylogenetic tree is a diagram that depicts the evolutionary relationships connecting a set of organisms.

The “tree trunk” begins with a common ancestor, which then branches out to include all descendent lineages of that ancestor, culminating in the descendent species that are living today.

Question 7

Phylogenetic trees consist of branches and nodes. What do these depict?

Answer 7

The branch lines on a phylogeny trace the pathway of evolutionary lineages through time, while nodes depict where an ancestral lineage has split into two or more descendent lineages.

Question 8

How are the bird species within a bird field guide typically organized?

Answer 8

Bird field guides are meaningfully organized according to the most closely-related species.

In other words, birds of the same family / genus are grouped together.

Question 9

What are the SEVEN basic classification levels for birds?

Answer 9

Kingdom → Phylum → Class → Order → Family → Genus → Species.

Example: the taxonomy of a Mallard duck would look as follows: Kingdom Animalia → Phylum Chordata → Class Aves → Order Anseriformes → Family Anatidae→ Genus Anas → Species Anas platyrhynchos.

Question 10

What is a species?

Answer 10

A species is the basic, principal unit of biological classification.

Question 11

What are the THREE defining characteristics of a species?

Answer 11

Species have:

1. Very similar physical, behavioral, and genetic traits,
2. A history of recently shared ancestors, and
3. The continued ability to fully interbreed.

Question 12

What is taxonomy?

Answer 12

Taxonomy is the scientific classification of organisms.

Question 13

What TWO things does an avian systematist do when a new species is reported?

Answer 13

An avian systematist:

1. Describes the particular characteristics that define that new species as a distinct entity, and
2. Places the new species within a broader evolutionary tree (phylogeny) that includes other related species.

Question 14

What is a subspecies?

Answer 14

A subspecies (or race) is a group within a species that has become somewhat physically and genetically different from the rest of the group. However, they are still similar enough to interbreed with the rest of the species.

These physical and genetic differences often arise as a consequence of geographical separation, which is why we see regional differences in the plumage of, for example, Fox Sparrows, which are one of North America’s most variable passerines at eighteen recognized subspecies!

Question 15

What is a “morph”?

Answer 15

Morphs are individuals of a species that exhibit distinctive variations in plumage or markings, but co-exist in the same space within other members of their species. In other words, these variations aren’t a result of geographic separation and differential evolution.

For example, the light and dark morph of the Swainson’s Hawk; the white and blue morphs of the Snow Goose; and, one of the world’s most widespread and common examples, the polymorphic Rock (Feral) Pigeon.

Question 16

What is a monophyletic group or clade?

Answer 16

In evolutionary terms, a monophyletic group or clade is the complete collection of evolutionary lineages derived from a single ancestral species.

Question 17

What are sister taxa?

Answer 17

Sister taxa are a pair of species with no closer relatives.

For example: humans and gorillas are sister taxa and are more closely related to one another than either is to chimpanzees or baboons.

Question 18

Individual bird species are classified two ways. What are they?

Answer 18

Birds are given (1) a binomial scientific name and (2) a common name in English. Sometimes they can accumulate several common names in both English and the local language of their region.

For example: In Jamaica, the Snowy Egret (Egretta thula) is known as the ‘Golden Slippers’ because of its yellow feet. In North America, the Common Loon is called the Great Northern Diver in Eurasia.

Question 19

What is the Linnaean System?

Answer 19

The Linnaean System is a binomial classification system that indicates genus and species, with genus capitalized and both words in italics.

For example, the scientific name for House Sparrow is Passer domesticus.

Question 20

List FOUR criteria scientists consider when deciding upon a name for a new bird.

Answer 20

Birds are typically named after:

1. Their region/habitat: Northern Cuckoo, Southern Boubou, Swamp Sparrow, etc.
2. The local language / dialect (Cuckoos = “rain birds” in Jamaica)
3. A distinctive trait of the species (‘Hadeda’ ibis = their call)
4. The name of an influential scientist (Cooper’s hawk = naturalist William Cooper)

Question 21

What is ‘lumping’ and ‘splitting’?

Answer 21

‘Lumping’ and ‘splitting’ are both colloquial terms for changes in biological classification.

Lumping is when two taxa that were previously thought to be separate species are merged into one species.

Splitting is when a single species that was previously thought to be only one is split into two or more different species populations.

Question 22

What is speciation?

Answer 22

Speciation is the evolutionary process by which one ancestral lineage splits into two or more descendant species.

Question 23

What does ‘population’ refer to in ornithology?

Answer 23

A population is a group of interbreeding birds of the same species that live in the same place, at the same time.

Question 24

What are species concepts?

Answer 24

Species concepts are precise sets of criteria that systematists use to tell whether two populations are the same or different species.

Question 25

Explain the TWO species concepts used in ornithology.

Answer 25

1. The biological species concept places the greatest emphasis on the ability of two populations to interbreed. When they can no longer interbreed due to their biological differences, they are considered different species.
2. The phylogenetic species concept defines a species as an irreducible group (smallest possible unit) whose members are descended from a common ancestor and who all possess a combination of defining traits.

Question 26

What is allopatry?

Answer 26

Allopatry refers to two organisms that occur in separate regions with no geographic overlap.

Question 27

What are species complexes?

Answer 27

A species complex is a group of closely-related organisms that are similar in appearance, yet exhibit subtle physical and genetic variations.

Fun fact: Species complexes could very well indicate a singular species is in the process of diverging into many distinct species.

Question 28

What does extant mean?

Answer 28

Extant means still living / still in existance.

Question 29

Phylogenies of birds are based on careful analyses of specific characters that are shared or variable among groups. What is meant by “specific characters”?

Answer 29

Characters are any heritable traits that can be compared among different groups of birds, such as the presence of a particular patch of plumage, a distinctive behavior, or a DNA variant at a particular location in the genome.

Question 30

What are the two character categories used by avian systematists to reconstruct a bird species’ phylogeny?

Answer 30

Prior to the availability of genetic technology, avian systematists studied morphological characters as a way to reconstruct phylogenies.

Today, however, genetic characters are most often used to study living birds because DNA sequencing can be used to infer their genetic relationships with one another far more accurately.

Question 31

Why can’t we use genetic technology to study dinosaur DNA?

Answer 31

DNA molecules degrade over time so we cannot study dinosaur DNA.

Cool story: At 12,000 to 13,000 years old, the moas from New Zealand are the oldest birds successfully analyzed using DNA technology. These enormous terrestrial birds disappeared after humans landed on the island and hunted them to extinction 700 years ago. Scientists were able to perform DNA sequencing of egg shells, feathers, preserved skin fragments, and bone and discovered between 9 and 11 moa species.

Question 32

What are nucleotides?

Answer 32

Nucleotides are the basic molecular building blocks of DNA and RNA. Their precise order in a region of the DNA molecule is called a DNA sequence.

Question 33

What is mitochondrial DNA?

Answer 33

In birds, mitochondrial DNA is found not in the cell nucleus, but rather in the cell’s mitochondria, a structure involved in generating energy within the cell. This part of the genome is passed down only from mother birds to their offspring.

Question 34

What is a genome?

Answer 34

A genome is an organism’s complete set of genetic instructions.

Each genome contains all of the information needed to build that organism and allow it to grow and develop.

Question 35

What are DNA barcodes and what can they be used for?

Answer 35

DNA barcoding is a method of species identification using a short section (or sequence) of DNA from a specific gene/s.

The premise of DNA barcoding is that, by comparison with a reference library of such DNA sections, an individual sequence can be used to uniquely identify an organism to species, in the same way that a supermarket scanner uses the black stripes of the UPC barcode to identify an item in its stock against its reference database.

Question 36

How does genetic divergence happen within a bird species?

Answer 36

Genetic divergence happens when populations are geographically separated from one another and few or no individuals move between them.

Over time, each population evolves its own set of genetic differences, which can become pronounced enough to lead to speciation. (The more genetically distinct two populations are, the longer they have been isolated from one another.)

Question 37

What is phylogeography?

Answer 37

Phylogeography is the scientific study of the evolutionary relationships of populations and species across space (rather than time) usually as inferred from genetic information. This study tells us about the processes that leads to species divergence.

Question 38

What is range disjunction?

Answer 38

Range disjunction is a pattern of geographic distribution in which two or more occupied areas are separated by substantial intervening areas where the species is not found.

This wide but patchy distribution tends to give rise to a lot of genetic variation.

Question 39

What geographical features and factors can give rise to range disjunction?

Answer 39

Range disjunctions is prevalent in bird populations that become separated by physical barrers and topographical features like mountain ranges, wide rivers, oceans, and islands.

It also happens in bird species that are restricted to habitats that act like islands within a matrix of other habitat types.

For example, birds that can only live at certain high elevations can be scattered into isolated populations throughout a mountain range.

Question 40

True or false:

Birds that occupy the forest canopy tend to exhibit MORE genetic differentiation than those who occupy the understory.

Answer 40

False.

Birds that occupy the forest canopy tend to exhibit LESS genetic differentiation because they move can more freely and widely to search for fruit and other resources. This promotes gene flow across a wider area—even barriers like rivers and mountains—resulting in less genetic differentiation.

Birds in the understory, however, exhibit more genetic differentiation because they are bound by barriers, move around much less freely, and tend to occupy ecological niches.

Question 41

What are the THREE concrete generalizations we can make about bird diversity worldwide?

Answer 41

1. The larger the area, the greater the bird diversity. A larger area likely supports a greater range of habitats and more resources.
2. The nearer the equator, the greater the bird diversity. The tropics support a greater diversity of habitats, niches, and food resources = faster species divergence.
3. Islands support fewer breeding bird species than continental areas of the same size. Not all types of birds can colonize islands successfully. Also, extinction rates on islands are higher because their populations are so isolated.

Question 42

What is the latitudinal diversity gradient?

Answer 42

The latitudinal diversity gradient is the general rule that in most groups of organisms, species diversity is greatest in the tropics and steadily decreases towards the earth’s polar regions.

Question 43

What is a biogeographical realm?

Answer 43

Biogeographical realms are characterized by their broadly similar faunas, avifaunas, floras, and evolutionary histories, which are unique and distinct from the other realms.

Question 44

Name the EIGHT primary biogeographic realms, using this map for guidance.

Answer 44

Nearctic, Neotropical, Afrotropical, Palaearctic, Oceanic, Australasian, Antarctic, and Indomalayan.

Question 45

What is Wallace’s Line?

Answer 45

Named after biologist Alfred Russel Wallace, Wallace’s Line is the most famous barrier to dispersal between distinct biogeographical realms. It occurs at the shared boundary of the Australasian and Indomalayan tectonic plates.

Interestingly, where very little dispersal has occurred across this line, other realm boundaries—like the nearctic and neotropical realms—have no single, clear breakpoint to indicate where bird faunas are diversified.

Question 46

What is the Great American Interchange?

Answer 46

Around 3 million years ago, the (Panama) land bridge connecting North and South America emerged from the sea, allowing organisms from both continents to disperse and mix rapidly.

Birds that don’t usually disperse across water were also able to begin breeding across this boundary line.

Question 47

What are the THREE broadest-ranging LAND birds?

Answer 47

1. The Peregrine Falcon is found on every continent except Antarctica;
2. The Barn Owl is found on five continents; and
3. The Barn Swallow breeds on 4 continents and visits 2 on migrations.

Question 48

What are the THREE broadest-ranging WATER birds?

Answer 48

1. The Wilson’s Storm-Petrel,
2. Arctic Tern, and
3. Sooty Shearwater
   * These three water birds have annual migration cycles that span most of the world’s five major oceans.*

Question 49

What are FIVE factors that determine the limits of a bird’s distribution?

Answer 49

Factors that determine the limits of a bird’s distribution include:

1. Preferred habitat (where do they thrive?)
2. Preferred climate (what temperature and water distribution can they tolerate?),
3. Availability of fundamental resources (food, water, and nesting sites),
4. Competition with other species,
5. Threats from parasites, pests, or predators.

Question 50

What do distribution maps in bird field guides tell us about the occurrence of birds in a region? And what’s important to remember about these maps?

Answer 50

Distribution maps tell us about the likelihood of a particular bird species being found within a shaded area, for a particular time of year. The closer you are to the boundaries of these areas, the lesser the probability of seeing that species.

These maps miss an enormous amount of detail and totally fail to capture the heterogeneity in bird distributions. It’s important to understand what these maps are telling us about the distribution of a bird species before allowing them to be the deciding factor in an ID.

Question 51

How do scientists attempt to understand bird diversity?

Answer 51

Diversity can be explored by comparing groups or orders of living birds with high and low diversity to determine whether certain aspects of their biology are associated with their differing levels of diversity.

Question 52

In evolutionary biology, what is meant by “key innovations”?

Answer 52

Key innovations refer to newly evolved traits that allow a lineage to take advantage of new ecological opportunities. This results over time in that lineage diversifying into multiple species that are specialized for those new ecological niches.

At some point in their evolution, the ability to fly became a key trait, enabling the bird ancestor to be vastly more successful than its contemporaries, leading to the enormous diversity of birds we see today.

Question 53

Describe the typical pattern of diversification exhibited by birds.

Answer 53

The common pattern of diversification involves a pulse of early and rapid speciation as a bird species move into and colonize a new area ripe with resources; followed by a decreasing pace of further speciation over time as resources and habitat are used up by ecologically competing species.

Question 54

What does sympatry mean?

Answer 54

Sympatry refers to organisms or groups of organisms that occur in the same place.

Sympatry is the antonym of allopatry, which means that ranges do NOT overlap.

Question 55

Define density-dependent diversification.

Answer 55

Density-dependent diversification is the concept that speciation within a group slows down over time as the number of species increases, since the presence of existing species blocks opportunities for new species to arise.

Question 56

What ancient common ancestor did all birds evolve from?

Answer 56

Birds evolved from therapod dinosaurs.

Many lines of evidence in the fossil record—including similar physiological traits and inferred behavior—strongly suggest that birds constitute a subgroup of the dinosaurs that arose fairly late from within the broader dinosaur radiation.

Question 57

When did dinosaurs originate and why did they go extinct?

Answer 57

The dinosaurs were a diverse group of reptiles that originated about 230 million years ago, became the dominant group of land animals, and were then mostly wiped out in the Chicxulub meteorite impact 66 million years ago at the end of the Cretaceous Period.

Question 58

What were theropod dinosaurs?

Answer 58

Theropod dinosaurs were a bipedal dinosaur clade characterized by hollow bones and three-toed limbs, and ranged in size from the crow-sized Microraptor to the huge Tyrannosaurus rex.

Question 59

How far back do the earliest theropod fossils date?

Answer 59

The earliest theropod dinosaur fossils date from the Late Triassic Period about 225 million years ago.

Question 60

Are birds dinosaurs?

Answer 60

In evolutionary terms, dinosaurs and birds are both more correctly considered a subset of the reptiles. Therefore, it’s technically correct to say that “birds are living dinosaurs” or that “birds are reptiles”.

Question 61

Which famous fossil discovery helped scientists make the link between dinosaurs and birds?

Answer 61

The evolutionary affinity between birds and dinosaurs was recognized with the discovery of the fossilized Archaeopteryx, the earliest known bird.

Question 62

From which theropod group did birds evolve?

Answer 62

Birds arose within the group Maniraptora, which had bird-like features.

Question 63

True or false:

Crocodiles are the nearest living relatives of modern birds.

Answer 63

True.

From the broader archosaur group that once included non-avian dinosaurs, pterosaurs, crocodiles, and birds, only crocodiles and birds have survived to the present day, making them each other’s closest living relative!

Question 64

Name FOUR morphological traits that birds and theropod dinosaurs shared.

Answer 64

1. Feathers: most lineages of theropod dinosaurs sported feather-like quills and plumes
2. Furcula: fused clavicles or “wishbones”
3. Hollow, tube-shaped, or pneumatized bones (filled with small air cells)
4. A small genome relative to most other vertebrates
   * The size of certain bone cells correlates strongly with the size of an animal’s genome: that’s how scientists are able to measure the size of dinosaurs’ genomes, even though no genetic material remains of them to be studied.*

Question 65

What are some explanations for the evolution of pneumatized bones in the theropod dinosaurs?

Answer 65

Pneumatized bones were long thought to be avian adaptations arising from selection for flight but we now know that these features evolved in non-flying dinosaurs too.

In the largest dinosaurs, these bones may have served to reduce the weight of the huge skeletal structures needed to support their massive bodies. In other, smaller theropods, they were more likely related to an active, fast-moving lifestyle.

Question 66

Name five physiological and behavioural traits that birds and theropod dinosaurs shared.

Answer 66

1. Upright, bipedal posture,
2. Rapid growth rate of young individuals,
3. Details of the structures of their calcified eggs,
4. Guarding and incubating eggs, and
5. Possibly also being endothermic.
   * Endothermic or “warm-blooded”: metabolically able to maintain a higher core body temperature than their surroundings.*

Question 67

Give FIVE examples of ancient birds that proliferated towards the end of the Mesozoic Era, before the mass extinction event that ended the Cretaceous Period.

Answer 67

1. Archaeopteryx (discovered in southern Germany)
2. Confuciusornis (discovered in China): a crow-sized Mesozoic bird with pointed wings and a long tail plume.
3. Hesperornis (discovered in western North America): highly-specialized swimmers with large, lobed feet; long, torpedo-shaped bodies; and small wings (most likely flightless).
4. Enantiornithes: one of the most diverse and successful groups of Mesozoic birds. Found on all continents except Antarctica, these songbird-sized birds had both aquatic and terrestrial lineages.
5. Ichthyornis: A strong flier and fish-eating equivalent of modern seabirds, about the size of a tern (with teeth).

Question 68

What event in the Late Cretaceous Period lead to a sudden turnover in the avian fossil record?

Answer 68

The devastating meteorite impact that ended the Cretaceous Period 65.5 million years ago caused the extinction of all dinosaurs, except for a few surviving bird lineages.

The fossil record shows that many archaic bird lineages that were common in the late Cretaceous are absent in the Tertiary.

Question 69

What happened to the few bird lineages that survived the cataclysmic event that wiped out the dinosaurs?

Answer 69

The few surviving lineages of modern birds diversified rapidly in the very early part of the Tertiary, as the environment became more hospitable, proliferating across a largely unpopulated planet with widely available resources, ecosystems without competition, and few threats and predators.

This period of very rapid radiation in the early Tertiary gave rise to many modern orders and families of birds.

Question 70

What is a molecular clock?

Answer 70

A molecular clock leverages the idea that DNA changes accumulate at a relatively steady rate, and that the genetic differences amongst organisms can therefore be used to estimate the time in the past when they began to diverge from one another.

Question 71

What is a ghost lineage?

Answer 71

A ghost lineage is an evolutionary lineage that is inferred from phylogeny, but for which no fossil evidence has been found.

Question 72

What is a crown group?

Answer 72

A crown group is the smallest clade that includes all living members of a group descended from the last common ancestor of a larger clade.

Question 73

List the Mesozoic Era’s THREE periods in chronological order.

Answer 73

1. Triassic Period (245 - 208 mya)
2. Jurassic Period (208 - 144 mya)
3. Cretaceous Period (144 - 65 mya)

Question 74

The Cenozoic Era, which followed the Mesozoic Era, is divided into two Periods: the Tertiary and Quaternary Period.

List the Tertiary Period’s FIVE epochs in chronological order.

Answer 74

1. Paleocene Epoch (65 - 54 mya)
2. Eocene Epoch (54 - 38 mya)
3. Oligocene Epoch (38 - 23 mya)
4. Miocene Epoch (23 - 5 mya)
5. Pliocene Epoch (5 - 1.8 mya)

Question 75

The earliest split in the tree of living birds separates which two avian bird groups from each other?

Answer 75

The earliest split in the tree of living birds separates the paleaognaths (ratites and tinamous birds) from the neognaths (all other bird species).

Question 76

What are the ratites?

Answer 76

The ratites are a group of heavy, flightless birds defined by their absence of a keel bone.

Ostriches, kiwis, emus, cassowaries, rhea, and the recently-extinct moas and elephantbirds are ratites.

Question 77

What was Gondwana?

Answer 77

Gondwana is the name given to the ancient southern supercontinent of 180 - 600 million years ago that includes most of present-day Africa, Antarctica, Australia, India, Madagascar, New Zealand, and South America.

Question 78

What is a species?

Answer 78

A species is the basic, principle unit of biological classification.

Question 79

What is a species?

Answer 79

A species is the basic, principal unit of biological classification.

Question 80

How many species of birds are there in the world?

Answer 80

Approximately 10,000 globally

Question 81

Define

Phylogenesis

Answer 81

The evolutionary development and diversification of organisms

or of a particular feature of an organism

Think: family tree!