Read this section and check the treatments of some familiar birds. Because the information in the treatments is concentrated, it will take a little practice before you gain access to all of it rapidly.
ESSAYS
At the ends of essays we have cross-referenced other related essays. We have tried to list the most closely related essay first, especially where it gives more general background information. For instance, the essay "Parasitic Swallows" deals with swallows laying eggs in the nests of other members of the same colony—an example of "brood parasitism." The first essay cross-referenced at the end of "Parasitic Swallows" is "Brood Parasitism," which gives a more general discussion of the phenomenon. References at the ends of the essays direct you to further readings on the same general topic.
SPECIES
Treatments of the nearly 650 species that regularly breed north of Mexico are the main section of this "book". Decisions on which species to exclude were sometimes "judgment calls". Note also that we have included treatments of those species known to have gone extinct in North America in historic times. Each treatment is divided into three parts:
1. Treatment Heading
The first part of the heading consists of the common name of the species, followed by its latinized "specific" name. The latter consists of two parts, a generic name (always capitalized) and a specific name (never capitalized). The generic name identifies the immediate group to which the bird belongs, and the specific name denotes the exact member of the genus. The latinized name of the American Robin is Turdus migratorius. Turdus is a genus of large thrushes; other members of that genus include Turdus merula, the Blackbird of Europe, and Turdus grayi, the Clay-colored Robin, which occurs casually in the southern tip of Texas but is excluded from this guide as a nonbreeder. Following the specific name is the name of its author—the person who first applied the latinized name to the species. (The year it was first applied has been added by Thayer Birding Software). Linnaeus, the father of scientific taxonomy, was the first to apply a two-part latinized name to the American Robin, so it is called Turdus migratorius Linnaeus. We include the authors not just for preciseness, but for your convenience in familiarizing yourself with the fascinating history of North American ornithology. [Common and Scientific names have been changed to match the currently accepted names as specified by the American Ornithologists Union as of August 2005.]
2. Summary Line
Immediately beneath the heading is an abbreviated, partly pictorial "summary line" presenting a combination of symbols, words, abbreviations, and numbers that supplies at a glance the following basic information:
(1) Typical nest location and height.
(2) Type of nest.
(3) How sexes divide the task of nest building.
(4) Whether eggs are marked or unmarked.
(5) Usual number of eggs in a clutch.
* (6) Predominant type of breeding system (whether the species is monogamous, a cooperative breeder, etc.).
* (7) How sexes divide the task of incubation.
* (8) Usual number of days from start of incubation to hatching.
* (9) Stage of development at hatching (precocial/altricial).
*(10) Usual number of days between hatching and fledging.
(11) How the sexes divide the task of caring for the young.
(12) Major types of food eaten during the breeding season.
(13) Basic methods of obtaining food (foraging).
* Items 6 - 10 were moved to the Treatment Paragraph in this ONLINE VERSION.
More details on interpreting the summary line are given below. Note that in the summary lines we use M to indicate the male, and F to indicate the female. Plurals are simply shown by doubling the codes: MM = males; FF = females.
3. Treatment Paragraph
The largest part of the treatment, a paragraph giving expanded information on the biology of the species, follows the summary line. The sequence of topics is: BREEDING habitat and number of broods per year; a brief description of DISPLAYS that might be observed (in species with numerous recorded displays this will be a sample only); characteristics of the NEST and its construction; color, markings, and average size of EGGS; CHICK DEVELOPMENT (#6 through #10 above were moved to this position in this ONLINE VERSION); DIET; CONSERVATION status, wintering range if it extends south of the U.S.-Mexico border, comments on human interference, and, if parasitized by cowbirds, its relative frequency as a cowbird host; NOTES of interest in addition to the previous categories; ESSAYS in this book that are especially relevant to the species; REFERENCES listed in the bibliography that provide access to the literature pertaining to the species.
There is a great deal of information in the ornithological literature that is only anecdotal and in need of confirmation, and much in books designed for birders that is inaccurate. Where we have presented unconfirmed information in either the summary line or the treatment paragraph it is accompanied by a question mark. We also have used question marks when we ourselves have made an extrapolation. For instance, those hummingbird species that have been studied have been found to be promiscuous, and we have designated most unstudied hummingbird species as "PROMISC?". Our policy has been to use such guesswork (always accompanied by the "?") where information from a closely related species can help make a strong inference about a species that has been less studied. It is critical to keep in mind, however, that even closely related birds can be remarkably different in their biological attributes, and that projections of the behavior of one species based on that of a close relative can be dead wrong. Throughout the treatments you should consider the "?" to be a signal to alert you to an opportunity to contribute to the knowledge of avian biology. A question mark in parentheses in the summary line applies to the full range of numbers or to both sexes that precede it. For example, "MF?" means the participation of the female is uncertain; "MF(?)" means the uncertainty extends to both sexes.
Be alert to the possibility that exceptions to the information given in the summaries may occur. If we report that the typical range of nest heights is between 20' and 30', with a total range of 5' to 50', do not assume that a nest at 3' or 55' is necessarily that of another species; recorded ranges are seldom all-inclusive.
Finding something that differs markedly from the information given is a sign that caution and careful observation are called for. If you just saw a Carolina Wren lay an egg in an open cup nest, double check the identity of the bird; it would be an unusual event indeed, but not impossible.
What follows is a key to the treatment summary line and then a detailed description of the treatment paragraph.
Key To The Summary Lines
(1) NEST LOCATION: Since many species are quite flexible in situating their nest, the symbol often represents only the most likely location. The symbol for the primary site is given at the left-hand margin of the summary line. Secondary locations are indicated by words or abbreviations shown below that symbol. These words are shown in the list beginning on the next page just under their symbols. For a very few unusual sites the location is given by a word only (no symbol). In the summary line, the numbers just under the location information indicate the most likely height in feet above ground, and the numbers in parentheses (if present) indicate the general range of heights at which nests of the species have been found. The heights indicated apply only to those nest locations given above the numbers, not below. A species whose nests are found in trees as high as 50 feet, in shrubs, and on the ground will be shown as O'-50'.
Note that in this key the most abbreviated form of a word is always given, although where space permitted we spelled words out in the summary line.
Locations Defined by Topographic Features:
Bank. Includes river banks, areas of soft soil on steep island slopes, etc., where nest burrows are excavated.
Ground. Includes nests placed among the roots, or in niches among the roots of fallen trees, among tules and reeds (in marshes), among grasses, on bare rock, or simply scraped in the dirt or sand.
Cliff. Includes nests situated in natural crevices or on ledges of cliffs typically offering a commanding view of a defensible position, and sometimes chosen when no suitable trees are available.
Locations Defined by Supporting Plant Structures:
Shrub. Includes nests placed within any multi-stemmed woody plant (i.e., one that does not have a distinct single trunk extending several feet between the ground and the lowest branching point).
Deciduous tree. Includes nests placed in any broad-leaved tree, whether it sheds all of its leaves in the fall ("deciduous") or not ("live"): oaks, maples, poplars, hickories, magnolias, etc. Also used for species that use broad-leaved and coniferous trees more or less indiscriminately.
Coniferous tree. Includes nests placed in any tree that bears cones: pines, spruces, junipers, firs, etc.
Snag. Nests in a standing dead tree. Also used for species that use cavities in dead and live trees more or less indiscriminately.
Vine tangle. Includes nests in vines, brambles, brush piles, etc.
Floating on water. Almost always anchored to live emergent or submerged vegetation.
(2) NEST TYPE: The symbol shows the type of nest most frequently used by that species. Birds of the same species tend to construct similar nests, but the materials available often differ from area to area. (See essays: Masterbuilders; Nest Materials; Nest Lining.) Secondary nest types are listed beneath the symbol and usually discussed in the treatment paragraph.
Scrape. A simple depression usually with a rim sufficient to prevent eggs from rolling away. Those of many duck species are almost bowl-shaped. Occasionally with lining added.
Cup. Typical of songbirds, this is the archetypal "bird nest." Hemispherical inside with a rim height several times the diameter of the eggs. In some cases bulky, but always with a deep depression.
Saucer. A shallow cup with the height of the rim not more than two times the diameter of the eggs. Also a flattened nest of pliable vegetation as in some wetland birds.
Platform. A structure in a tree, on a cliff, or providing a dry place above marshy ground or water, usually big enough for the bird to land on, with or without a distinct depression to hold the eggs. Typical of many raptors and birds of wetlands.
Cavity. Either excavated, as is typical of woodpeckers, or natural cavity found in dead or dying limb or tree. Sometimes a cup or other structure is built within.
Crevice. Eggs placed in a crack in the face of a cliff, between boulders, in a human-made structure, etc.
Burrow. Eggs placed in a chamber at the end of a tunnel. Tunnels either excavated by the birds (most kingfishers, puffins, storm-petrels) or usurped from small mammals, especially ground squirrels and prairie dogs.
Pendant. An elongate sac-like nest suspended from a branch.
Spherical. Globe-shaped or ball-shaped. A roughly round structure, fully enclosed except for a small opening usually on the side or at one end.
(3) WHO BUILDS THE NEST: The male (M) and/or female (F) code(s) below the nest symbol indicate which sexes participate in nest building. If both sexes participate, but one does much more than the other, there is a minus sign (-) preceding the symbol of the less-involved sex, and that sex is presented second. In cooperative breeders, if birds other than the breeding adults help with construction, there is a plus sign (+) following the codes for the breeding adults.
(4) EGGS: The gray egg symbol is used if the eggs have markings, the white egg symbol if it is unmarked. The number(s) just below the symbol indicate the most common clutch size, or the range (there is often individual and/or geographic variation in clutch size). The number(s) in parentheses below that line or to its right indicate more extreme values recorded in the literature. In many species the data on clutch size are limited. Furthermore it is often difficult to determine when clutch sizes at the higher end of the range indicate the production of two or more females laying in the same nest (we have tried to exclude such values here), and when clutch sizes at the lower end of the range indicate incomplete production. Clutch size can also be affected by a female's age, by whether the clutch is produced early or late in the season, by whether it is the female's first clutch or a replacement clutch, as well as by other factors (see essays: Average Clutch Size; Variation in Clutch Sizes; Brood Parasitism; and Cooperative Breeding).
(5) MATING SYSTEM: The following abbreviations found below the clutch size listed beneath the drawing of the egg indicate which breeding system is typical for the species.
MONOG Monogamy. One male mates with one female (see essay: Monogamy).
POLYGYN Polygyny. One male mates with two or more females (see essay: Polygyny).
POLYAND Polyandry. One female mates with two or more males (see essay: Polyandry).
PROMISC Promiscuity. Males and females mate more or less indiscriminately (see essays: Promiscuity; Leks).
POLYGAM Polygamy. Both polygyny and polyandry occur.
COOP Cooperative. Two females rear broods in the same nest simultaneously and/or non-breeding birds serve as helpers at the nest of one or more breeding pairs (see essay: Cooperative Breeding).
Monogamy is, by far, the most common mating system in birds, and unless there is evidence to the contrary, we have assumed a species to be monogamous. Note that very often a small percentage of birds in a population deviate from the mating system of the majority. It is not, for example, unusual in an otherwise monogamous population to find 5 percent of the males polygynous. Conversely, in virtually every population of a polygynous species there will be at least a few monogamous pairs. In our classifications, unless at least 15 percent of the birds use the minority system (given in parentheses), it usually will not be identified in the summary line. Here again, careful observations are needed to see if nonmonogamous systems, especially polygyny, are more widespread than currently thought.
[Please note: In the online book, items #6 through #10 below are described in the discussion following Eggs, rather than at the top of each screen.]
(6) INCUBATING SEX: The male (m) and/or female (F) codes at the top of the fourth column of the summary line indicate whether both parents, or only one parent, incubates. As in nest construction, if both sexes are involved but one spends much more time on the nest, there is a minus sign (-) before the symbol of the less-involved sex, and it is listed second; in cooperative breeders, if birds other than the breeding adults are involved, there is a plus sign (+) following the symbols of the pair.
(7) LENGTH OF INCUBATION: The number(s) following the "I:" are the usual number of days (or recorded range of days) from the start of incubation to hatching. Note that hatching of a clutch is often synchronized by delaying the start of incubation until the last egg is laid. Incubation time is somewhat geographically variable within species, and your accurate observations could add to our knowledge of that variation. Numbers appearing in parentheses represent recorded extreme values.
(8) DEVELOPMENT AT HATCHING: Birds show great variation in their degree of development at hatching, and we show the maturity of hatchlings for each species on the line under the incubation time. In North America there are no fully developed (PRECOCIAL 1 ) young at hatching. Our most fully developed young at hatching are classified "PRECOCIAL 2," exemplified by ducklings and shorebird chicks. They are downy, open-eyed, mobile at birth, and find their own food while following their parent(s). At the opposite extreme, our songbirds are "ALTRICIAL"—born naked, immobile, and wholly unable to feed themselves.
Developmental patterns are explained fully in the essay Precocial and Altricial Young. In North America seven conditions of young at hatching are found:
PRECOCIAL 2 Mobile, downy, follow parents, find own food.
PRECOCIAL 3 Mobile, downy, follow parents, are shown food.
PRECOCIAL 4 Mobile, downy, follow parents, fed.
SEMIPRECOCIAL Mobile, remain at nest, fed.
SEMIALTRICIAL 1 Immobile, downy, eyes open, fed.
SEMIALTRICIAL 2 Immobile, downy, eyes closed, fed.
ALTRICIAL Immobile, downless, eyes closed, fed.
Other than in the summary line, the word "precocial" used alone in this guide refers to the first four categories collectively; similarly the word "altricial" refers collectively to the last three categories.
(9) TIME FROM HATCHING TO FLEDGING: The number(s) under the development pattern, following an "F:", are the usual number of days (or recorded range of days) until precocial young are able to fly competently and the time required before altricial young leave the nest (altricial species may not be able to fly competently when they depart the nest). Numbers in parentheses represent recorded extreme values. Again, fledging times are variable and your accurate observations may be useful. Note that fledging rarely means the end of parental care. Precocial young of some species, such as oystercatchers, stay with and are helped by the parents long after they can fly; after they have left the nest, altricial young may be fed more than twice as long as they were fed in the nest.
(10) WHO TENDS THE YOUNG: How the parents divide the feeding (and guarding) of the young is shown just under the hatch-to-fledge time. For precocial species whose young are not fed by the parents, this indicates who tends the young while they feed. The letters coding the sex of the tending parent are the same as those used in (3) above.
(11) DIET DURING BREEDING: The symbol shows the primary type of food eaten during the breeding season. Secondary types of food commonly taken may be shown by words or abbreviations below the symbol. Many of these words are shown in the list below just under their symbols. Additional specific food items taken less frequently are listed in the treatment paragraph and details of primary food types are often given there (since the symbols cover broad categories). Remember, many species have an entirely different winter diet, and if so, this is usually described in the treatment paragraph.
Animal Foods Include:
Small Mammals. Anything from shrews to ground squirrels and rabbits, but most often rodents.
Birds. May include their eggs—if so, that will be mentioned in the treatment paragraph.
Small Terrestrial Lower Vertebrates. Includes reptiles (lizards, snakes, etc.) and amphibians (salamanders, frogs, etc.).
Fishes. Sometimes includes fry and eggs, in which case that usually will be mentioned in the treatment paragraph.
Terrestrial Invertebrates. May include insects, spiders, mites, snails, slugs, worms, millipedes, sowbugs, etc. Usually predominance of insects.
Aquatic Invertebrates. May include aquatic insects, crayfish, shrimp, snails, bivalves, etc.
Carrion. Prey found dead.
Plant Foods Include:
Nectar. The sugary solution found in many flowers.
Fruits. Includes berries, which are simple fleshy fruits.
Greens. May include leafy parts of both aquatic and terrestrial plants.
Nuts. Hard, dry, single-seeded fruits, often acorns and beechnuts.
Seeds. Includes grains, sunflower seeds, conifer seeds, etc.
Omnivorous. A variety of plants and animals too diverse to specify here; neither plant nor animal food usually comprises less than one-third of diet.
Many birds, especially passerines that eat both seeds and insects, take proportionately more insects when seasonally available. Although seed-feeding birds frequently consume gravel to aid in grinding seeds, we have not included grit in our description of diets.
(12) FORAGING TECHNIQUES: The major method each species uses to obtain food during their breeding season is the last symbol on the right in the summary line. The symbol is often supplemented by a word or abbreviation that indicates less frequently used foraging techniques. These words are shown below just under their symbols. In the case of foraging techniques we again find gaps in the record, offering ample opportunities to provide the missing information. Note both primary and secondary techniques may be used to obtain primary food items.
Techniques for Picking Food from Ground Surface or Plants While Walking or Clinging Include:
Ground Gleaning. Picking up items from the surface of soil, turf, sand, etc. Includes scavenging dead aquatic organisms from shorelines.
Gleaning from Foliage and Occasionally from Branches. Takes invertebrates and/or fruit from vegetation, not from the surface of the ground.
Gleaning from Tree Trunks and Branches. Describes foraging that only rarely includes removal of invertebrates from foliage as well. Includes excavating and drilling into bark.
Hovering Techniques Include:
Gleaning while Hovering. Takes nectar, insects or berries from plants above the ground while hovering.
Hovering and Pouncing. Hovering before swooping or dropping down on prey.
Other Flying Techniques Include:
Hawking. Sallies from perch on short flights to capture flying insects.
Aerial Foraging. While in prolonged continuous flight, captures flying insects.
Aerial Pursuit. Chases and catches birds in midair, stoops (drops on flying birds from above, killing them in midair with a blow from the talons), or snatches them from their perches.
Swoops. Snatches up prey from ground in talons after gliding descent from perch with wings spread.
High Patrol. Soars at high altitude in search of carrion or prey.
Low Patrol. Seeks prey in low searching flight.
Aquatic Techniques Include:
High Dives. Drops from height into water, usually to catch fish, but sometimes to take waterfowl or other prey.
Skims. Flies low over water (Black Skimmers' lower mandibles penetrate surface); and snatches up fishes or aquatic invertebrates.
Surface Dives. Floats and then dives; swims underwater using feet and/or wings.
Surface Dips. Takes food from the water's surface or from just below while floating or swimming on the surface.
Dabbling. Floating on surface in shallow water, pivots headfirst downward while raising hindquarters above water to reach submerged plants or animals on or near substrate (mud, sand).
Stalks and Strikes. Hunting by standing motionless on bank or in water and spearing fishes, frogs, etc.
Probes below Surface. Foraging for food beneath surface of substrate (mud, sand) either in or near shallow water. Also often includes taking food from within the water column.
INTERPRETING THE TREATMENT PARAGRAPHS
As in the summary line, the information in the treatment paragraph is also necessarily condensed, so you should be aware of the following assumptions. First, birds are complex, adaptable animals, and although certain aspects of behavior within some species are relatively stereotyped, many vary as local environmental conditions vary. Thus a species that normally lines its nest with fine grasses may substitute a bit of fleece snagged on a barbed-wire fence surrounding a sheep pen or shredded plastic insulation from an old power cable, if either is conveniently near the nest site. In addition to behavior, the physiological, reproductive, and other biological characteristics of most widespread birds vary geographically. For instance, a species may raise only one brood per season in the northern part of its range, but rear two or even three farther south. Within a species, clutch and egg sizes may differ between birds nesting in desert regions and those in well-watered localities. Western coastal populations may have access to insects during the rather mild winters, while east coast representatives may be restricted mostly to berries after the first hard frost.
Thus, because space limitations in the book prevent detailing these patterns of variation, we present the most common biological features and behaviors, and try to indicate the range of variation. But not every individual will fall within a given range.
The statements in the paragraph are telegraphic (condensed words and sentences), and most of the material is self-explanatory, but keep the following in mind:
BREEDING: Only the breeding habitat—where nesting occurs—is given. Birds may very often be found in quite different kinds of environments when foraging, after breeding, during migration, or in the winter. The habitat description is followed by the number of broods per season.
DISPLAYS: Courtship has not been systematically described in many birds, particularly those active at night. If described in the literature, we attempt here to give at least some major features of courtship displays. In addition, as you will see in various essays, displays used in courtship and in aggression are frequently similar. For this reason, we will often describe displays that you might observe without ascribing a function to them. Because of space constraints, in many cases you will have to infer the form of the display from its name (e.g., "head pumping" meaning moving the head up and down). Careful observations of display behavior and the contexts in which it occurs are badly needed for many species.
NEST: Positions of nests (e.g., relative to the trunk for cup nests in trees) are often listed, as are alternate sites, but materials used tend to be so extremely variable (see essays: Nest Materials; Nest Lining) that they usually have been condensed to a minimum. In most cases we indicate whether nests are reused for subsequent broods within a season or whether nests are reused in successive years (nest is "perennial"). Often the amount of time required to build the nest is given.
EGGS: These vary in color and markings, even within clutches. Colors may change as incubation advances, and eggs often become stained in the nest, particularly if situated on the ground. Egg identification thus is often very difficult even when a photograph is available. It is, however, usually easy to exclude many possibilities on the basis of our brief description of color, markings, and average size. Egg size (length) is given in both inches (") and millimeters (mm). Remember that one inch is 25.4 mm, so that eggs described in the literature as 37, 38 or 39 mm long will be recorded as 1.5" due to our rounding. Conversion to inches was done before averages in mm were rounded to the nearest nun. Note that egg size is also variable: if one species is listed as having a size of 19 mm and another of 18 mm, it is quite likely that some eggs of the first species will be smaller than some of the second species, and vice versa. If, on the other hand, one species is listed as 19 mm and the other 25 mm, egg size will provide a pretty good clue to which species' nest you are observing. Also bear in mind that eggs may vary in size with the order in which they are produced and that eggs from early clutches often tend to be larger than later ones. Above all, remember it is illegal to disturb the eggs of most species without appropriate permits.
DIET: This usually expands the information on breeding-season diet presented in the summary line, may list foods eaten during the nonbreeding season if different, and occasionally adds brief comments on foraging. Animal prey usually are listed first, followed by plant matter. Very often items given in the summary line are not repeated here.
CONSERVATION: Information about the wintering range provides important clues about the future conservation status of migrants traveling to Latin America where accelerating deforestation and other forms of habitat destruction are increasingly evident and may greatly affect the size of breeding populations within "our" area. Therefore we describe here the wintering range in some detail if significant numbers of North American individuals spend the nonbreeding season outside of the United States and Canada. If the species is resident or migrates within our area, this is stated briefly. Migrating birds occasionally stray far off course, but we have excluded "casual" or "rare" sightings since they are not important to the species' conservation status. Critical as wintering grounds can be to the survival of a species, remember that many threats to the persistence of our avifauna involve human activities within the United States and Canada.
Significant documented interference by humanity (hunting, habitat destruction associated with the encroachment of civilization and concomitant land, water, and food contamination, competition from introduced species) is also included here, as are efforts that are, or could be, implemented to circumvent such interference. Inclusion in The Blue List or Endangered Species status (see Birds and the Law), is noted here as well.
Standard enemies are not discussed here. Given the chance, predators such as domestic cats or Sharp-shinned Hawks will snatch up any small bird; and foxes, raccoons, jays, ravens, and many others will rob any nest they can. We do, however, note the degree of parasitism by cowbirds, since expansion of cowbirds' ranges has made them especially important enemies of some species, such as Kirtland's Warbler (see essay: Conservation of Kirtland's Warbler). We also indicate nest hole usurping by European Starlings, House Sparrows, etc., when it is thought to influence conservation status.
NOTES: In this section we include interesting additional information that does not conveniently fit elsewhere. In many cases some of the most important and unusual aspects of the biology of the species will be described here.
ESSAYS: Near the end of the treatment paragraph we list a few of the essays that seem especially pertinent to the species. For instance, after watching a hummingbird for a while you might wonder why it spends so much time perching—and you'll find an answer in the essay Hummingbird Foraging Bouts. Naturally, we can't list every pertinent essay in every species treatment, so each essay itself is cross-referenced to other essays on related topics. By referring to cross-linked essays we hope you will gradually (and relatively painlessly) acquire an overview of modern bird biology. To the same end, we have sometimes referred you to more general essays when the bird in question has relatively little known about its biology, and none (or only one or two) of the more specific essays are pertinent. We hope that each time you see an especially interesting bird in the field you will try to read some of the associated essays—in many cases they can greatly enhance your appreciation of the species you have under observation. For an overview of the topics covered in the essays, see Essays in Alphabetical Order.
REFERENCES: Citations in the original book are not included in this online book. We recommend that you obtain a copy of the book if interested in the references. The book is available from OnlineNatureMall.com