Higher Song Rates Research Articles

Endocrine correlates of alternative phenotypes in the white-throated sparrow ( Zonotrichia albicollis)

Many vertebrate species exhibit alternative phenotypes (or morphs), in which one sex displays phenotypic variation equal to or greater than the variation between the sexes. Males in such species typically display differences in reproductive strategies and morphology. Steroid hormones such as testosterone are known modulators of reproductive behavior and morphology and therefore are obvious candidates for the mediation of phenotypic differences between morphs. We conducted a year-round study in the white-throated sparrow ( Zonotrichia albicollis) that exhibits alternative phenotypes in plumage coloration and behavior in both sexes: during the breeding season, white-striped males and females are more aggressive and have higher song rates than tan-striped individuals. At the beginning of the breeding season, free-living white-striped males had higher plasma testosterone concentrations than tan-striped males. However, this finding might have been due to different social experiences because captive male morphs sampled at similar times of year did not differ in testosterone concentrations. Captive white-striped males had larger testis and cloacal protuberance sizes than tan-striped males, which might be related to the divergent mating strategies of the morphs. Male morphs showed similar increases in luteinizing hormone following injections of gonadotropin-releasing hormone, but white-striped males showed larger increases in testosterone, indicating differences between morphs in gonadal testosterone production. Females had low concentrations of testosterone, and morphs did not differ. Plasma dehydroepiandrosterone (DHEA) concentrations were elevated in both sexes and morphs during the breeding and non-breeding seasons. These data do not support the hypothesis that testosterone activates behavioral differences between alternative phenotypes in the white-throated sparrow. Alternative testable hypotheses include hormonal effects during early development and direct genetic effects.

Song as a signal to negotiate a sexual conflict?

AbstractSexual conflict occurs when the optimal solution regarding e.g. a life history trait differs between co-operating individuals of different sex. When deciding a conflict is not instantaneous, some form of negotiation can be expected to evolve. In great tits, Parus major, a sexual conflict exists over the number of clutches that are reared, because the fitness costs of a second clutch are greater for females. A conflict is also likely to exist over investment in the first brood - each parent benefiting from a greater investment by the partner. Male great tits sing when rearing the first brood, and if acoustic signals play a role in the negotiation of a sexual conflict, a positive association between male song rate and maternal investment is predicted. In agreement with this hypothesis, maternal effort (in kJ/day) relative to paternal effort was positively correlated with male song rate. Furthermore, females were more likely to start a second clutch when their male had a high song rate, and high song rate was associated with shorter inter-clutch intervals. Song rate was higher when brood size was experimentally reduced and, independent of brood size manipulation, males with high song rate produced higher quality fledglings. These results indicate that song rate reflects the males' state, suggesting it may function as a handicap signal. Although song rate seems too low (<4% of time) for honesty to be maintained by production costs alone, signalling costs may be amplified by the fact that song appears restricted to the time when the male and female are both near the nest. To achieve a high song rate, the male may have to spend a large amount of time near the nest, thereby seriously restricting time available for other activities.

Seasonal Variation of Singing Activity and Relative Effect of the Advertising Behaviour of Males With Different Plumage Colour in the Pied FlycatcherFicedula hypoleuca

Abstract. From late April to the second 10-day period of June 1994–1999, in 76 unmated males the time-budget was measured during 304 hours in a 6.6 km2 area of mature mixed and coniferous forests near Moscow. In 1999, territorial males were counted at least once per pentade throughout the breeding season in a 35 ha plot with 180 nest-boxes. Dark (grades 2–3 on Drost's scale) and pale (grades 5–7) males had similar levels of singing activity, but in cold weather the former had higher song rates than the latter. The singing activity of all the males was relatively low at the beginning of the season (by the mid-May). Dark males sang mainly from open perches (67.6% of songs, compared with 23.2% for pale males). In dark males visual stimulation compensated for the relatively low acoustic activity in early spring when trees were still lacking leaves. The immediate vicinities of nest-boxes occupied by dark males were visited by females significantly more frequently than those of pale ones.

Nightingales in space: song and extra-territorial forays of radio tagged song birds

Most temperate zone passerines defend territories during the breeding season. Commonly the size of these territories is estimated by plotting the singing locations of the males. However, an individual's activities need not be restricted to the area used for singing. So far, only little quantitative information has been available to determine how the singing territory relates to the activity range of male songbirds. Here, we present a study in which we used radio-tracking techniques to collect quantitative data on the spatial behaviour of 11 male territorial Nightingales (Luscinia megarhynchos). The results show that the singing territories made up only about 50% of the activity ranges. Nevertheless, males spent over 90% of the time within the singing territory. Singing territories almost never overlapped but activity ranges overlapped in all cases with the activity range of at least one neighbour. Males intruded into neighbouring territories throughout the season but the longest excursions were made before and during the female fertile period. The time spent for forays correlated significantly with song rate and territories of males with higher song rates in turn were less frequently the object of forays by other males. Song rate can be indicative of male quality, so that our findings strongly suggest that foray behaviour is related to male quality in nightingales.

Sexual selection in the zebra finch Taeniopygia guttata : condition, sex traits and immune capacity

The aim of this study was to test two hypotheses: (1) that condition-dependent secondary sexual traits reflect an individual's immune capacity and (2) that immune capacity and secondary sexual traits covary with primary sex traits, specifically ejaculate quality. We used the zebra finch Taeniopygia guttata as a study species, since the traits that females find attractive in males of this species, song rate and beak colour, are well established. A paired experimental design comprising 31 pairs of brothers was used; for each pair, one male was assigned to a control group provided with ad libitum food and no additional exercise, and the other male was assigned to an experimental group which experienced additional exercise and a reduced rate of food intake. After 11 weeks, the experimental group differed significantly from the control group in a range of variables, including body mass, haematocrit, granulocyte:lymphocyte (G:L) ratio and several primary sex traits, indicating that condition in this group was reduced. Birds in the experimental group showed a differential response to the treatment. We used the rank order in which birds could be captured by an experimenter as an index of condition. Birds easily caught were assumed to be in poorer condition than those which were more difficult to capture. Rank capture order was repeatable and was significantly correlated with the G:L ratio in the experimental group, but not in the control group. In the experimental group, rank capture order was correlated significantly with both secondary sex traits: birds in better condition had redder beaks and a higher song rate. However, beak colour and song rate did not covary significantly, suggesting that these two traits provide different types of information. Secondary sex traits did not covary with primary sex traits or any sperm features. Thus, there was no evidence for Trivers' sexual-competence hypothesis or the phenotype-linked fertility hypothesis. We used four assays of immune capacity, two general (G:L ratio and spleen mass) and two specific [antibody titres to sheep red blood cells (SRBCs) and Brucella abortus (BA)]. The G:L ratio was significantly higher in the experimental group, spleen mass (absolute and relative) did not differ between the groups, anti-SRBC antibody titres were significantly higher in the control group (contrary to expectation), and anti-BA antibody titres were close to being significantly lower in the experimental group. Within the experimental group, there was no evidence that antibody titres covaried with secondary sex traits. Although we demonstrated that beak colour and song rate were condition dependent, our experiment provided no evidence that either of these traits covaried with immune capacity or sperm features.

Song Rate Correlates With Paternal Care and Survival in Willow Tits: Advertisement of Male Quality?

Abstract Dawn song in birds may advertise male quality in terms of parental care and/or survival. Males who sing most may also be the best parents, and eager singing may also reflect good chances of a male's or his mate's survival. These relationships were studied in the willow tit Parus montanus, a species with a simple and relatively non-variant song. Song output was expressed as the proportion of time a male spent singing at dawn. Later in the breeding season, two aspects of parental care, nest defence and feeding effort, were measured in the same males. High song output was associated with more intense nest defence behaviour (eager singers attacked the predator model more often and approached closer to it) and high nestling feeding effort. However, reproductive success was not associated with song output, although males with high song rates tended to be more likely to produce recruits. Males who survived to the next year had higher song intensity than males who did not survive, while female survival was not correlated with song output of her mate. The results suggest that dawn song in the willow tit advertises male quality. Some aspects of honest advertisement and female choice are discussed.

Female mate choice in the zebra finch ? the effect of male beak colour and male song

Studies of female mate preference in zebra finches (Taenopygia guttata) have shown that male beak colour and song rate are important. However, the two characters are correlated. Here the effect of beak colour and song rate on female choice are examined independently. In mate choice tests involving two males, beak colour was manipulated artificially using nail varnish. The results showed that females showed a significant preference for males with a high song rate, but not with a red beak. Females did not prefer males with a red beak if song rate was low and females preferred males with orange beaks who expressed a high song rate. Female preference for males with red beaks was not found when beak and song characters were no longer correlated.

Diurnal song pattern in the Great Reed Warbler Acrocephalus arundinaceus

The diurnal song pattern of the Great Reed Warbler Acrocephalus arundinaceus was studied at Lake Kvismaren in South Central Sweden between 1985 and 1989. Males sing two types of song, a long song when attracting females and a short song when guarding fertile females. Seven males were studied over full 24-hour periods. The diurnal song pattern of males singing long song was characterized by a sharp peak in song rate at sunrise when they sang 70% of the time. In late morning song rate reached a plateau of about 55% of the time up till noon whereafter it slowly dropped to cease almost completely at sunset. An average male produced between 7,000 and 8,000 song strophes in a day. The song rate of individual males in noon and afternoon was clearly predictable from morning values, i.e. a male that had a high song rate in the morning was also likely to have a high song rate later the same day. In contrast to the long song, the short song was produced at a rather steady low level throughout the day and also appeared to be more variable in intensity over short time periods (i.e. showed a higher variance). The decline in the rate of long song over the day seemed to be paralleled by a decline in number of unmated females, suggesting that profitability of singing is highest during early morning whereafter it levels off. These results are discussed in relation to several hypotheses explaining diurnal song pattern in birds.

The Relationship Between Individual Differences in Male Song Frequency and Parental Care in Blackcaps

Abstract Song rates in male blackcaps were examined over the course of the breeding season and compared with various aspects of mating and later parental behavior in individual birds. Song rates decreased steadily over the breeding season although relative individual rates remained constant. Early territory holders sang more and mated faster than late-comers. Song frequency was positively related to alarm call frequency during nesting but negatively related to male incubation and offspring feeding rates. Surprisingly, under the conditions studied, higher song rates were indicative of higher nesting success. This demonstrates the potential role of song frequency in the advertisement of territorial quality. There may well be either environmentally dependent differences in parental care as adaptations to temperature, food or predation pressure or simply a trade-off for males between singing and parental care, where early arriving males derive greater fitness benefits from singing, while late arriving males benefit more from engaging in parental care.

Female zebra finches choose extra-pair copulations with genetically attractive males

One way that sexual selection for genetic benefits could operate in monogamous species is through female choice during extra-pair copulations (EPCS). EPCS are common in monogamous species, and field studies are consistent with the hypothesis of females choosing genetically attractive males for EPCS. Here I show that female zebra finches actively solicit and perform EPCS with males that are more attractive than their mates. Attractive males have higher song rates, have sons with higher song rates, and fledge heavier offspring. This provides a mechanism for sexual selection in monogamous species, and is consistent with `good genes' models of sexual selection.

Mate choice in the willow warbler ? a field experiment

Females may choose a mate on his own quality or on the quality of his resources, i.e., his territory. We removed willow warbler males and allowed new males to settle, before the arrival of females, in order to test whether the proximate cue for female choice was any male trait or territory characteristics. The experiment indicates that females base their choice on some male trait. No correlation was found between male settlement order and size (tarsus length, wing length), but males arriving early were in better body condition than males arriving late. The most likely male trait for female choice was singing rate, which was a good indicator of male settlement date. The duration of time between mating and egg laying was shorter in early territories, both in the observational and the experimental data. Since male song rate was correlated with territory quality (e.g., food abundance) the ultimate benefit to females choosing males with high song rates could be a high quality territory.

Basal song rate variation in male red-winged blackbirds: sound and fury signifying nothing?

Male red-winged blackbirds (Agelaius phoeniceus) vary substantially in how much they sing. We tested whether song rate reflected the male’s quality, the quality of his territory, or his frequency of interaction with potential competitors. Song rate declined with the seasonal decline in nest initiations, suggesting that song is used to attract females. However, males with higher song rates did not obtain larger harems. This suggests that females do not use male song rate to assess either male quality or territory quality. If song rate signals male quality to male rivals, and if territory owners are of higher quality than floaters, then owners' song rates should be higher than those of floaters. However, when we removed territory owners temporarily, the song rate of their floater replacements was similar to that of the original owners. Finally, a male’s song rate was not affected by how frequently he chased intruders, or by the proximity or number of neighbors he had. In short, the only information that basal song rate of redwinged blackbirds appears to provide to conspecifics is that the territory is occupied. In simulated territory takeover attempts, however, song rate was significantly higher than the basal rate. Thus, more may be revealed by the singer in these situations. [Behav Ecol 1991;2:123-132]

Variation in the song rate of the male pied flycatcher Ficedula hypoleuca: causes and consequences

The natural song rate of the pied flycatcher, Ficedula hypoleuca, was highly correlated with both air temperature and time of day as well as with date of season. The average song rate at different temperature levels rose as the season advanced. When temperature, time of day and date were held constant, males were found to slightly increase the song rate during the premating period. The average song rate did not correlate with age, tarsus length (body size) or colour type of the male. Males provided with extra food considerably elevated their song rates at low temperatures in relation to controls which indicates that song rate is limited by food resources. Under natural circumstances, females selected males that had been the longest in the area and also males with the highest song rates, even after the correction for augmented song rate with duration of premating period. It is suggested that the female, in selecting a male with a high song rate, in fact may select either the food content of his territory and/or the quality of the male directly. Alternatively, female mate choice may be based on territorial cues, and song rate and/or male quality may merely be correlatives of territory quality.