J. David Ligon

Territory Quality and Dispersal Options in the Acorn Woodpecker, and a Challenge to the Habitat-Saturation Model of Cooperative Breeding

The central feature of cooperative breeding systems is the presence of one or more nonbreeding birds in a social group that devote time and energy to help raise the offspring of other group members. The most widely accepted model for the evolution of this behavior is that it arises when there is some ecological constraint to independent breeding by young birds that otherwise would disperse from their natal groups. Among territorial species, this constraint is usually hypothesized to be saturation of suitable habitat by sedentary established groups. We use data collected over a 10-yr period to test this model for a population of acorn woodpeckers (Melanerpes formicivorus) in central New Mexico. Acorn woodpeckers store large quantities of mast, and territories vary greatly in the amount of storage facilities present. Storage facilities significantly affect the survival and reproductive success of groups occupying those territories. Most helpers occur in high-quality territories; low-quality territories are frequently unoccupied and thus available for colonization. We estimate lifetime direct and indirect offspring production for yearlings that help in territories of differing quality and for varying numbers of years. Birds that forgo individual reproduction for one or more years in high-quality territories but eventually breed there can have greater lifetime fitness than those that disperse at 1 yr of age and breed immediately in low-quality territories. Had we combined data from all territories and all groups, these findings would have been obscured; rather, the resulting calculations would have erroneously indicated that, for yearlings, dispersing and breeding is always the preferred option. Our analyses indicate that habitat saturation or some other constraint on the opportunity to breed successfully is not required to explain the existence of cooperative breeding in this population of woodpeckers. Instead, we suggest that competition for space may be the outcome of factors that promote philopatry, such as access to a critical resource and/or mutualistic benefits of living in a group and eventually breeding in the natal territory. If this scenario is correct, habitat limitation is a result of other factors favoring cooperative breeding rather than the basis for this kind of social system.

Male-male competition, ornamentation and the role of testosterone in sexual selection in red jungle fowl

Abstract Ornamental traits related to success in male-male competition were studied in red jungle fowl, Gallus gallus. In controlled fights between pairs of males, comb size was the only morphological trait that correlated with winning. Among free-ranging, socially integrated groups of 1-year-old males, body size and comb chroma (degree of saturation with pigment), in addition to comb size, were significantly related to dominance. In jungle fowl, the comb is strongly affected by blood testosterone level, which in turn reflects the current physical condition of the individual.

Effects of experimental manipulation of male secondary sex characters on female mate preference in red jungle fowl

In previous mate choice experiments, female red jungle fowl, Gallus gallus, preferred males with long, bright red combs, red eyes, and (in one case) long tail feathers. When the colour and/or length of the comb was manipulated experimentally by placing artificial Latex combs over the natural ones, hens seemed to ignore the manipulated character and focused instead on traits such as hackle feather colour that had been secondary in importance in previous mate choice tests conducted with unmanipulated birds, but not as much so as the comb or eye characters. Similar results were obtained when tail length was experimentally lengthened or shortened. Rather than using only one or two traits as criteria of choice, females may rely on an additive or redundant suite of characters, with each providing part of the information used in making mate choice decisions.

Evolution of Avian Plumage Dichromatism from a Proximate Perspective

Several studies have indicated that sexual plumage dichromatism is a result of four proximate mechanisms: estrogen, testosterone, luteinizing hormone, and nonhormonal factors. In estrogen‐dependent dichromatism, dull plumage coloration develops in the presence of estrogen, while bright coloration develops in its absence. In testosterone‐dependent and luteinizing hormone–dependent plumage dichromatism, bright plumage develops in the presence of these hormones, while dull plumage develops in their absence. Placing the proximate control of plumage dichromatism in a phylogenetic context suggests that estrogen‐dependent plumage dichromatism, found in the avian orders Struthioniformes, Galliformes, and Anseriformes, is likely to be ancestral in extant birds, while plumage dichromatism dependent on testosterone, luteinizing hormone, or nonhormonal factors is a more derived condition. An examination of the possible pathways leading to estrogen‐dependent plumage dichromatism suggests that the fewest evolutionary steps are to begin from a condition in which both sexes are more brightly colored, followed by selection for duller coloration in one sex. The fact that estrogen‐dependent dichromatism is ancestral in extant birds suggests that more brightly colored monochromatism may have been ancestral in modern lineages of birds.

Sexual Differences in Foraging Behavior in Two Species of Dendrocopos Woodpeckers

Two recent studies on woodpeckers (Kilham, 1965; Selander, 1966) support the hypothesis of Rand (1952), which states that within a species sexual dimorphism may aid in reduction of competition for food. In an extensive discussion of intraspecific differences in foraging, Selander (1966: 143-145) diagrams the solutions open to birds faced with decreased availability of food, and Kilham (1965) discusses possible causes, other than those directly related to food supply, for the evolution of traits that reduce intersexual competition for foraging sites. Neither author discusses in detail the problem of origin of stereotyped behavioral differences between the sexes. Sexual differences in foraging behavior of two species of Dendrocopos, the Red-cockaded Woodpecker (D. borealis) and the Arizona woodpecker (D. arizonae), are described in this report, and a discussion of the possible origin of this phenomenon in woodpeckers is presented. These two species differ greatly in the degree of sexual dimorphism of body size and bill length, to which much importance has been attached (Selander and Giller, 1963; Selander, 1965, 1966). The Red-cockaded Woodpecker inhabits open pine forests of the southeastern United States. It is found only in areas where pines predominate and is probably most common on the Atlantic coastal plain. The range of this species extends northward to Virginia and Kentucky, and westward to Oklahoma and Texas (A.O.U., 1957). The range of the Arizona Woodpecker extends from extreme southern Arizona and New Mexico, where it is associated with oak woodland, south into Michoacan (Davis, 1965: 537).

Parasites and male ornaments in free-ranging and captive red jungle fowl.

The morphology and parasite burdens of culled free-ranging red jungle fowl (Gallus gallus) from the San Diego Zoo were compared with those of captive roosters used previously in sexual selection experiments, to determine if results obtained with the captive birds were relevant to more natural situations. Zoo roosters had three helminth gut parasites: Ascaridia galli, tapeworms, and Heterakis. Parasite distribution was generally over-dispersed, with most individuals having none or few worms and some having heavy parasite burdens. These levels were comparable to those artificially induced in test roosters. The appearance of the zoo birds was similar to test roosters as well. Higher parasite burdens in the zoo birds was negatively related to hackle feather redness, comb length, and especially testis volume. The latter finding is discussed in light of information about the relationship between testosterone levels, sexual selection, and the immune system. A new analysis of female choice of uninfected controls versus experimentally infected roosters suggests that females prefer a multivariate array of traits perceived as a continuous, rather than categorical, variable.

Mate choice by female red junglefowl: the issues of multiple ornaments and fluctuating asymmetry

The significance of multiple ornaments of male birds and other animals is currently not well understood. Male red junglefowl, Gallus gallus, possess a number of morphological traits that appear to be ornamental in nature. These traits include components of the colourful plumage and fleshy structures on the face and head, the single, medially-located comb, paired wattles and ear lappets. Some studies have implicated the comb in the mate choice decisions of female junglefowl, and some have also indicated that plumage of males is not important in this regard. To test for a possible role of other male morphological ornaments in female mate choice, and to evaluate the earlier counterintuitive findings concerning male plumage, we controlled comb size, and experimentally manipulated plumage, wattles and ear lappets of male red junglefowl. We also tested responses of female junglefowl to asymmetry of bilaterally paired male ornaments by manipulating the symmetry of the paired wattles, ear lappets and the ornate hackle feathers of the neck. None of these manipulations provided evidence that female red junglefowl are sensitive to asymmetry of paired ornaments of males. A series of tests involving a male with pronounced body asymmetry likewise produced negative results. In contrast to some other studies on birds, we obtained no evidence that female red junglefowl use symmetry of either ornamental or non-ornamental traits in mate choice decisions. Comb size, the only male trait shown to be used by females, both in the present study and in some earlier ones, did not correlate significantly with natural asymmetry in any of several measured traits. Copyright 1998 The Association for the Study of Animal Behaviour.

Reciprocity in the green woodhoopoe (Phoeniculus purpureus)

Abstract Green woodhoopoes ( Phoeniculus purpureus ) exhibit behaviours that appear to meet all the criteria of reciprocity. In this species social units typically are composed of one breeding pair plus a variable number of helpers. A helper (X) that feeds nestling Y often is repaid by Y via Ys critical assistance in the acquisition of territorial ownership and breeding status by X; Y later also feeds the offspring of X. This pattern follows whether or not X and Y are related. Unrelated adult woodhoopoes of the same sex also may merge to form new social units, with the younger, lower ranking bird helping the older to acquire and retain territorial space. Later, it also provides care for the older birds offspring. It is here suggested that a population structure based on a combination of cooperatively-breeding groups and high rates of mortality have favoured the evolution of reciprocal exchanges between unrelated individuals.

ECOLOGICAL ENERGETICS OF THE PUERTO RICAN TODY: HETEROTHERMY, TORPOR, AND INTRA‐ISLAND VARIATION

The extremely small size (5–7 g) of todies, together with their taxonomic affinities (Order Coraciiformes) and tropical distribution, suggest that the thermoregulatory physiology of these birds merits detailed investigation. Here, we present results of a study on body temperature regulation and metabolic rate of one species, the Puerto Rican Tody (Todus mexicanus). Basal metabolic rate (BMR) was 3.24 ± 0.59 mL O2·g−1·h−1 (mean ± 1 sd), ∼33% higher than predicted on the basis of mass, but within the range of BMRs reported for other small birds. However, many other aspects of the todys thermoregulatory physiology are unusual. (1) Average active-phase body temperature (Tb) was 36.7 ± 1.2°C, well below the avian norm of 40–41°C. (2) Todies exhibited heterothermy; over a range of ambient temperatures (Ta) from 15° to 40°C, body temperatures varied from 27.9° to 42.9°C. At low Tas, Tb of some individuals decreased by as much as 10–11°C during nocturnal hypothermia; these birds remained active and alert, indic...

The Role of Phylogenetic History in the Evolution of Contemporary Avian Mating and Parental Care Systems

Although adaptation via natural selection is accepted by evolutionary biologists as the primary basis for the great diversity of functional traits exhibited by organisms, its potency does have limitations. Wilson (1975:32) refers to the limits to evolutionary change or the relative difficulty of altering rates of evolutionary change as phylogenetic inertia and points out that this inertia imposes constraints on the evolution of new adaptations. Some biologists have viewed “phylogenetic constraint” as a weak explanation either for why particular traits are present or for the absence of characters that would appear to make the organism in question better adapted (e.g., Alcock, 1979:174). However, over the past few years it has become increasingly apparent that a consideration of the evolutionary history of many traits, including social and reproductive behavior, is essential to the development of a comprehensive understanding of the relationships between organisms and their environments.