Unmated Birds Research Articles

The fractal dimension of a conspicuous ornament varies with mating status and shows assortative mating in wild red-legged partridges (Alectoris rufa).

Complex body designs, such as plumage ornaments in birds, can be described by fractal geometry. These complex patterns could have a role as visual signals during courtship and social interactions, but an empirical validation in the wild is currently lacking. Here, we investigated whether the fractal dimension (FD) of a complex plumage pattern displayed by red-legged partridges Alectoris rufa could function as a potential sexual signal. We captured wild birds early in the breeding season and tested if mated and unmated birds differed in the FD of their conspicuous melanin-based black bib. We also tested if the FD of the black bib was correlated within the pair, looking for evidence of assortative mating based on the expression of this trait. We simultaneously assessed similar effects in other ornamental traits (black bib size, white throat patch and black flank band surface, redness of the eye rings and bill). Mated birds showed higher black bib FD values than unmated ones. Mated males, but not females, also displayed a larger black bib. Moreover, the black bib FD (but not the trait size) and the white throat patch surface showed assortative mating. Finally, females with higher black bib FD showed smaller black flank band surface, suggesting a trade-off in the expression of the two melanin-pigmented plumage traits. This provides unique and novel indication for the shape complexity of a pigmented trait, here described by its fractal dimension, to be potentially under sexual selection in a wild animal.

Females and males respond more strongly to duets than to female solos: comparing the function of duet and solo singing in a tropical songbird (Icterus icterus)

Abstract Both females and males of many animals possess elaborate displays, such as solo songs and duets of songbirds. We know little about the function of female song or what selects for duets. To examine their possible functions, we played female solos, duets and a heterospecific control to pairs of troupials (Icterus icterus). Both sexes responded strongly to duets by approaching the playback speaker significantly closer, faster, and more often compared to female solos or the control. Neither sex responded strongly to female solos; troupials approached closer, sang sooner, and duetted more following female solos than the control, but this difference was not significant. Our results indicate that troupial duets pose a greater threat than female solos and female troupial solos are not particularly threatening. Troupial duets may be especially threatening because they indicate the presence of a mated pair, which likely poses a greater territorial threat than lone, unmated birds.

The use of nest departure calls for surveying Swamp Sparrows

Female Swamp Sparrows (Melospiza georgiana) give a loud series of chips as they leave their nest during incubation and brooding. I tested the efficacy of basing breeding population surveys on the nest departure call (NDC). For a subset of point-count surveys designed to estimate the abundance and distribution of Swamp Sparrows in the coastal mid-Atlantic States, I surveyed singing males and (in a longer survey) the number of different females uttering NDCs. A set of 31 points was surveyed in early June and a subset of 21 in early July. The number of NDCs was well correlated with the number of singing males detected in the early season. The number of females giving NDCs was consistently smaller than the number of singing males. In part, this is because the detection distance for NDC is significantly shorter than for male song. However, even within a small fixed circular plot, more males were detected. Singing-male surveys provide more data over a shorter period of time and are appropriate for large-scale surveys. However, female NDCs provide an index of actual reproductive activity with no unmated birds included. Although a longer survey period is required, the surveys can be conducted throughout the day. It is suggested that female vocalizations related to nesting activity are more widespread than is generally appreciated and, when possible, should be used at least as complementary data to singing-male surveys.

Territory switching behavior in a sedentary tropical passerine, the dusky antbird (Cercomacra tyrannina)

Demographic data from an 8-year study of a marked population showed that switching territories and mates is common in both genders of dusky antbirds (Cercomacra tyrannina), a sedentary neotropical passerine with year-round territories and pairbonds. We conducted 22 experimental removals and followed six natural disappearances to examine territory switching. Antbirds quickly abandoned territories and mates to move to openings created by experimental removals. Pairing with the resident on a new territory was rapid. Unmated birds attracted new mates by singing a gender-specific song that differed from songs given by mated birds. There were no gender differences in replacement time or rate. Some vacancies, experimental and natural, were not filled, suggesting that floaters were rare. Territory and mate switching were not related to immediate enhancement of reproductive success because the probability of reproducing successfully was equally poor on all territories. Territory switching may be an overlooked but common tropical form of territoriality that increases individual survivorship during periods of low food abundance (dry season). We suggest that switching is favored when low annual reproductive success enhances selection for a long lifespan as the primary means to increase reproductive success. Key words: Aves (birds), removal experiments, RHP, territory switching, mate switching, mate choice, genetic monogamy, Cercomacra tyrannina, tropical passerine, antbird. [Behav Ecol 11:648–653 (2000)]

Long-Term Viability of the Re-Introduced Population of the White-Tailed Eagle Haliaeetus albicilla in Scotland

The white-tailed eagle became extinct in Scotland early in the twentieth century after persecution by humans. A population has been re-established in western Scotland by the release, mainly as juveniles, of 82 wild-bred birds imported from Norway between 1975 and 1985. Some released immatures wandered widely, but birds settled on fixed home ranges within 100 km of the release site on Rum, usually at 3-4 years old. In 1992 there were c. 19 individuals, including eight pairs, occupying fixed home ranges. There was also an unknown number of immature birds. Annual survival rates were estimated at 73% for young birds prior to settlement and 94% thereafter from the observed numbers of released and established birds. However, estimates were imprecise because of the small size of the population and the lack of reliable individual marks. By 1992 a total of 29 young had been fledged in the wild from five home ranges. None of these young have yet bred. The mean breeding success of released birds increased with age up to 0.465 fledged young/pair/year at about 6 years old. There was significant variation in breeding success among individuals and/or home ranges. 13% of bird-years of occupation of fixed home ranges involved either unmated birds or supernumeraries in the home ranges of pairs, creating trios. A simulation model indicated that the observed proportion of unmated birds was similar to that expected from differences in the numbers of males and females arising by chance. It was estimated from the available demographic data that the population would be more likely to grow slowly than decrease if stochastic effects due to small population size did not operate. However, the 95% confidence interval for the estimated population multiplication rate encompassed decline at 11% per year and growth at 11% per year. Simulation models indicated that, with realistic assumptions about variation among individual birds or ranges and demographic parameters set at their maximum-likelihood values, there was a probability of about 0.6 that the present population would become extinct within 100 years. Only conditions which would permit population growth at 2-3% per year in the absence of stochastic, small-population effects would reduce the probability of extinction within 100 years to less than 0.1. Simulation of supplementary releases of imported juveniles indicated a substantial reduction in extinction risk from the release of a further 60 juveniles. Variation in the rate of release, within a range considered feasible (10 birds per year -1 or 20 birds year -1 ), had little effect on this result.

Effect of Mating Activity on the Ability of Salmonella enteritidis to Persist in the Ovary and Oviduct of Chickens

Experiments were undertaken to determine whether female leghorn chickens that had been mated had a lower incidence of salmonellae colonization in the ovary, oviduct, internal organs, and eggs than did unmated birds from the same flock when both were inseminated with Salmonella enteritidis-contaminated semen. Eggs were sampled at approximate 3-day intervals, and fecal samples were taken at 24 hours and 7 days after insemination. Fourteen days following insemination, hens were euthanatized and the ovary, oviduct, liver, spleen, gall bladder, and ceca were removed. None of the previously mated hens had salmonellae present at any sampling time. Virgin birds showed salmonellae colonization in all samples. This indicates that mating activity and the environment of females offers some protection against salmonellae colonization in the reproductive tract.

Do common ravens yell because they want to attract others?

The formation of groups at food bonanzas results from a variety of mechanism, which include recruitment by signalling and information parasitism. Recruitment is distinguished from information parasitism on functional grounds: attraction of a crowd is termed recruitment if the signaler's fitness is enhanced by the attraction of others but termed parasitism if the signaler's fitness is reduced by the attraction of others. We here show, however, that in Common Ravens, Corvus corax, the proximate reasons for giving recruitment signals are probably other than for attracting a crowd. In the forests of the northeastern United States, non-breeding, vagrant ravens commonly aggregate in large numbers at carcasses where they neutralize the defense of territorial adults. We attempted to mimic this situation with a captive flock of juveniles and a pair of resident adults in order to determine the proximate factors triggering “yells”, vocalizations which attract nearby ravens to large animal carcasses. Our experiments indicate that yells are given primarily by hungry birds. However, yelling is strongly modified by status. Within the vagrant crowd, status is labile. When successive dominants were removed, replacements immediately took their place. Furthermore, when the dominants were re-introduced to the flock they always suffered significant losses of status and ceased yelling. The territorial male has, and constantly maintains, the highest status within (but not necessarily outside) his territory, and here he rarely yells. In sharp contrast, within the vagrant crowd of unmated birds it is the highest-status birds that are the most likely to yell when approaching food. Furthermore, the dominant vagrants (as well as adults) suppress yelling in subordinates. We conclude that ravens yell proximately to advertise their status at food, and that recruitment is only one of several ultimate advantages of the behavior.

Social Attraction in Nesting Least Terns: Effects of Numbers, Spacing, and Pair Bonds

These experiments examined the role of colony numbers, spacing pattern, and mating status on the social attraction of Least Terns (Sterna antillarum). Decoys were used to simulate different social conditions. Least Terns were more attracted to larger rather than smaller groups of terns, to terns spaced out at 1.5 m intervals rather than at 0.5 m intervals, to solitary rather than paired terns, and to plots containing single birds together with paired terns rather than to either alone. Taken together, these experiments suggest that colony size, spacing patterns, and mating status contribute to the relative social attraction of conspecific Least Tern groups. The specific choice of larger groups, larger interbird distances, and pairs plus singles allows (1) males to establish territories within the center of a colony, (2) both sexes to court unmated birds, and (3) both sexes to obtain maximum vigilance and antipredatory benefits from being in a larger group.

Plasma concentrations of prolactin during the breeding cycle in the Cape gannet ( Sula capensis): A foot incubator

Plasma prolactin was measured in the Cape gannet ( Sula capensis) which differs from most other avian species in that although both sexes share equally in incubation duties, neither sex possesses an incubation patch but rather incubates a single egg with its foot webbing. Five main categories of birds were studied: (1) nonbreeders, (2) unmated birds which were nevertheless defending a nest site, (3) recently mated birds, (4) incubators, and (5) brooders with nestlings. Prolactin titers in the plasma were 8–9 ng/ml in nonbreeding gannets, increasing to 17.7 ± 1.6 and 16.7 ± 1.2 ng/ml in incubating females and males, respectively. Plasma concentrations of prolactin progressively increased in nonbreeding gannets from 5.5 ± 0.4 ng/ml in 1-year-old birds to 8.7 ± 1.6 ng/ml in birds defending a nest site but without an egg. Blood samples taken from both incubators and nonincubators every 3 hr over 27 hr did not reveal any significant daily cycling in prolactin titers. Plasma osmolarity did not vary significantly between nonincubators and incubators, being 300.1 ± 3.2 and 298.2 ± 3.0 mOsm/kg, respectively. No positive correlation was found between possible osmotic stress during incubating and plasma concentrations of prolactin. Plasma concentrations of luteinizing hormone and testosterone increased while prolactin decreased, significantly, 24 hr after clutch loss. The putative inhibition of the pituitary-gonadal axis by prolactin is discussed together with other possible roles of prolactin during the breeding season in gannets.

Flight Song and Song Flight in the Orange-Crowned Warbler

Birds of many species commonly sing while flying. The behavior is characteristic of many open-country species, such as larks, pipits, and Bobolinks (Dolichonyx oryzivorus) and also occurs among some woodland species, including several wood warblers (Parulidae; Ficken and Ficken 1962). In some of these warbler species, both the given during flight, and the itself, are distinctly different from perch and direct flight. Ficken and Ficken described such as a variable warbling [accompanied by a] rising on slowly flapping or quivering wings [and] typically a direct and silent descent. Workers have reported flight songs and song occurring in several species of Vermivora, including the Tennessee Warbler (V. peregrina; Bowdish and Philipp 1916), Nashville Warbler( (V ruficapilla; Bowles and Bowles 1906, and Thayer, reported in Chapman 1907), Bachman's Warbler (V. bachmanii; Howell 1924, reported in Bent 1953), and Blue-winged Warbler (V. pinus; Pitelka 1939). The and flights described for these species, however, appear to be less modified than those described by the Fickens for nonVermivora warblers. I observed and flights occurring in the Orange-crowned Warbler (V. celata) during behavioral studies of the species in its typical nesting habitat in Contra Costa County, central coastal California. I followed the behavior of unmated territorial males prior to 12:00, during March, April, and May of 1980, 1981, and 1982. Although I may have overlookQd the behaviors, I did not observe and flights in unmated birds during late February, June, and early July, nor among mated birds during any month. Populations of these warblers were relatively dense in my study areas, with all males having at least two territorial neighbors. Territorial disputes were common. Most I heard were begun in mid-flight, and completed on a perch. Occasionally the entire was rendered in the air. I could detect, by ear, no difference between sung during and those sung entirely while perched. When in flight, the wings of a warbler characteristically fluttered or quivered in a way I never saw in normal direct flight. I observed nothing resembling the rising and direct descent described by the Fickens. I noted nine instances of birds singing while in during 260 min of observation in which the individual Orange-crowned Warblers were in sight. Since these birds usually sang four to six per minute, it is apparent that occurred much less frequently than perch songs. Flight and flights apparently occurred at random, and I noticed no associated special circumstances, such as the presence of a female or a competing male. The and flights I observed in Orangecrowned Warblers differed from those described by the Fickens. They generally resembled those described for other species of Vermivora, although the fluttering in has hitherto been reported only for the Nashville Warbler (Bowles and Bowles 1906). I am aware of only two reports of and behavior resembling those I have reported here occurring in parulids other than species of Vermivora. The American Redstart (Setophaga ruticilla) apparently has an and often associated with encounters with females or rival males (Ficken 1962). The Kirtland's Warbler (Dendroica kirtlandii) also has such and flights, but they do not seem to be associated with any special environmental context (Mayfield 1960:133). Relatively unmodified and now are reported for the majority of North American Vermivora, suggesting that these forms of behavior are characteristic of the genus.

Relationship Between Fat in Breast and Thigh Muscles and Skin with Abdominal Fat from Mated and Unmated Female Coturnix Quail

Coturnix quail chicks were hatched from randomly selected eggs and grown to adulthood. Forty-two mated and 13 unmated females were killed at 107 days of age. Correlations between abdominal, fat and fat measured at different locations (breast, thigh, crop collar) were high. Percentage thigh fat was 1.3 times that of breast fat. There was no difference (P>.05) between mated and unmated female quail for percentage fat and moisture content of breast muscle and skin and percentage fat content of thigh muscle. A highly significant difference was found for percentage fat and percentage moisture content of wet thigh skin between mated and unmated birds. The phenotypic correlation between percentage moisture and fat content in the breast muscle was −.76 and was −.94 in the breast skin in both mated and unmated females.Coturnix quail may be used as a pilot animal in body composition research provided due caution is taken because of the difference between species.

INTRASPECIFIC NEST PARASITISM IN BIRDS

Summary(1) The incidence of intraspecific nest parasitism in birds is reviewed. This phenomenon can be identified by various methods, ranging from biochemical examination of protein and enzyme polymorphisms to observations on the sequence of appearance of eggs in the nest as well as on the shape and colour of the eggs. The phenomenon has been reported for at least 53 species (Table I), mostly among precocial birds.(2) The evidence suggests that the parasites are (a) young, unmated birds, (b) females which have lost their nests and (c) mated females which also lay in the nests of other females. High proportions of such females, and scarcity of suitable nest sites increase the rate of parasitism.(3) Breeding success in parasitized nests is reduced by factors such as egg loss, desertion, inefficient incubation, reduced clutch size and late layings. The upper limit of the rate of intraspecific parasitism is discussed. It is argued that its incidence will be higher in the tropics than in extreme zones, for example, high latitudes and deserts, because there is higher synchronization of breeding in the latter, and increased predation in the former zones. Also, it will be more common in species which lay large clutches, such as precocial species.

The immediate effects of ditching a saltmarsh on nesting herring gulls Larus argentatus

We examined the effects of water management for mosquito control on the behaviour and breeding success of a resident colony of herring gulls. The colony resided on three close islands, one of which was ditched in March before the start of the second breeding season. The number of breeding pairs on the ditched island remained the same before and after ditching although the breeding number increased by 46% and 90% on the other two islands. Breeding chronology was similar on all three areas. However, birds nesting on spoil laid eggs a mean of 8 days later than non-spoil nesting birds. Behavioural observations on aggression and display rates indicated that birds on spoil behaved similarly to those in open grassy areas but differed from those nesting in the bushes. Nest site selection, breeding densities, and breeding success were similar on all three islands. Thus the differences noted were attributed to the appearance of the marsh. We postulated that pairs having nested on the experimental island in the previous year continued to do so after the island was ditched. However, pairs searching for new territory did not move onto the island that was ditched, but instead colonised the nearby islands. Similarly, those pairs breeding on spoil nested later because of the need to defend their nest sites which were situated in areas used for displaying by unmated birds.

The effects of ingested petroleum on oviposition and some aspects of reproduction in experimental colonies of mallard ducks (Anas platyrhynchos).

Compared to unmated mallard ducks fed an uncontaminated diet, unmated birds given food contaminated with 3 ml South Louisiana crude oil per 100 g dry weight showed an 84% decline in the daily rate of oviposition, a 33% decrease in egg-shell thickness and at autopsy more than 82% of the ovarian mass consisted of atretic follicles. Similar studies on groups of mated females showed that although the addition of 1 ml South Louisiana crude oil/100 g dry food had no effect on the daily rate of oviposition, none of the eggs had been fertilized while a concentration of 3 ml South Louisiana crude oil/100 g dry food suppressed the daily rate of oviposition significantly. Less than 25% of these eggs had been fertilized and only 40% of the fertilized eggs yielded viable ducklings. In both of these groups of mated birds, normal patterns of oviposition, fertilization and hatchability were restored after removal of petroleum from the diet. The addition of 1 ml Kuwait crude oil/100 g dry food had no effect on the rate of oviposition, the incidence of fertility or the hatchability of the fertilized eggs. The addition of 3 ml oil/100 g dry food completely abolished oviposition, but a normal rate of oviposition was restored when the concentration of the crude oil was reduced from 3 to 1 ml/100 g dry food. However, the incidence of fertilization remained low and none of the fertilized eggs gave rise to viable ducklings. Kuwait crude oil had no effect on shell thickness.

Home range structure of a population of Aegithalos caudatus

1. The structure and distribution of pair territories of Aegithalos caudatus in breeding season was studied. Then, the winter flock territory was discussed in comparison with them. The field studies were made at foot zone in 5 breeding seasons during 1964 and 1968. The habitat was mixed woods of middle Honshu, Japan, consisting of Quercus serrata, Castanea creata, Larix leptolepis and Pinus densifrora.2. Breeding territorialism was discussed with analyses on pair behaviors, distribution of activity loci, movements, fighting behavior and helpers.3. The pair formation behavior was not observed in spring but was confirmed in summer and autumn of the previous year. Pairs split from winter flock, and at interval stage of pair formation, one or several pair flocks existed. These flocks were involved within their common range of winter flock. The range of pair flock was communally defended by members of the same flock against adjacent such flocks. Pairs occur in the winter flock and gradually become isolated with each other, but never go out of the winter flock range.4. At night, all the pairs assemble to one winter roost, but during the day each of them is engaged in nest-building at separate place. In early spring, nesting is done only in the morning, returning to flock life in the afternoon, especially when the weather is bad.As breeding season advances, pairs remain more of the time in their own territories.5. Pair ranges established by dividing a winter flock range are considerably overlapped, especially at their previous center of the flock. The pair of dominant male first become independent against the group of pairs of subordinate males, which settle at or near the flock center.6. During early stage, all the pairs splitted from a common winter flock make a group and communally fight against the members of other such groups. At the stage of completion of outerwall of the nest, pairs roost in it and completely isolate themselves from the flock.7. The highest frequency of fighting is seen in nesting period when copulation occurs, and thus the territoriality in this species becomes the most evident and its territorialism is perfectly established. After that, the fighting frequency and territory size markedly decrease.Under such condition, the social structure settles and production of the next generation is under way. But, in reality, this stable condition is greatly disturbed by predation on their nests and various behaviors of renesting are resumed.8. A pair has a few central areas with highest activity density which never overlap with those of adjacent pairs. The patrolling course for maintaining the pair range starts from the central area and return to it. On patrolling along the periphery of the pair range, the pair would fly against the adjacent pair when they meet.9. The male show many available nest sites to the female who determines one of them as their nest. The male after this event performs several nest-invitation displays which remind behavior patterns of courtship and mating. The nest is not necessarily located at the central area, though in most cases it is found in or near it. Although the nest is made often in a branch of pine, typically it is concealed in a dense bush.10. Pairs renest when the first nest is destroyed, often beyond a few adjacent pair ranges. However, the site of renesting is never selected outside of the winter flock range and tend to be correlated with the previous activity range.11. In nestling and fledgling periods, the helpers are observed, but never before that. The helpers consist of unmated birds and unsuccessful breeding pairs. As soon as young birds become independent from the parents, the helpers and young birds make a family flock with the parent birds.

TERRITORY IN THE THICK‐BILLED NUTCRACKER NUCIFRAGA CARYOCATACTES.

Summary. The main features of the territory in the Thick‐billed Nutcracker are:‐ (a) the territory is kept for life and inhabited throughout the year; (b) the special food, nuts, is stored in the territory; (c) song, copulation, nest‐site selection and nest‐building take place only in the territory; (d) territories examined were 11.2–14.9 hectares, averaging 32.7 acres, believed to be the normal size in Sweden. There is no clear evidence that the territory has the function of securing more than a certain amount of food other than stored. The territory is respected by other Nutcrackers as to its main functions, while simple visits by other Nutcrackers and ceremonial gatherings in the territory are tolerated. Both territory‐holders attack intruders that try to take nuts but as they do not chase them out the behaviour is not regarded as truly territorial behaviour. The territory is proclaimed by the calls, the song being exclusively sexual. Unmated birds have not been recorded with territorial behaviour. When the special food is limited and the nesting habitat ample, the population is limited by the amount of the special food; but when the special food is abundant and the nesting habitat limited, over‐crowding seems to be prevented by territorial behaviour. It is suggested that the function of territory in the Nutcracker is to give the holders a well‐known refuge from predators, to serve as a food storing place, and by spacing out to prevent these positive qualities from reduction by overcrowding.

The Migrant Loons of Western Pennsylvania

BENT (1919: 48) says of the Common Loon (Gavia immer), loons are apparently paired when they arrive on their breeding grounds, and I believe they mate for life. The implication would seem to be that they migrate as mated pairs. Todd (1940: 32) says, loon is a rather solitary bird in our region (Western Pennsylvania), and a number together have a common interest rather than a sociable disposition. In the spring, however, presumably mated pairs may sometimes be encountered and on one occasion (May 1, 1932) Professor Seiple saw as many as twelve together on Conneaut Lake. This might be interpreted to mean that Todd construed Seiple's dozen as comprising six mated pairs, though I do not think Todd so intended it. However, in conversation, Dr. Parkes of Carnegie Museum expressed the opinion that a considerable proportion of migrant loons may be moving in mated pairs, along with a lesser number of unmated birds. My own observations seemed to lend no support to this view, and on the contrary, tended to the opposite view, that all loons migrate as independent voyageurs, though sometimes assembling into fortuitous flocks of various sizes. It seemed advisable to submit the full evidence to such mathematical treatment as might be helpful on this point. Material.-Western Pennsylvania from the West Virginia border north for a hundred miles or more, including the Pittsburgh area, contains few bodies of water attractive to loons: it is an upland country, much of it wooded, ranging in elevation from roughly 1,000 to 2,000 feet. None the less, the loons pass over it in some numbers, but they fly high, fast, and apparently silently, and are not often observed. I have seen one or two, traveling singly at a great height. The best opportunity to observe them is when they have alighted on some body of water, which happens frequently enough to give some idea of their behavior. The materials used in the present analysis are five years' observations at Oneida Dam, Butler County, in the years 1949 to 1953, inclusive. Most of the observations are my own, but some are by Mrs. Preston and others. An account of the water birds of Oneida Dam, including all migrant species, for the first four of these years has been given elsewhere (Preston, in press), and a map of the area is there included. It is shown that in the four years in question, the peak of the loon migration came at April 22, the standard deviation (of the timing) was 11.6 days,