Luis F. Baptista

Social interaction, sensitive phases and the song template hypothesis in the white-crowned sparrow

Naive 50-day-old white-crowned sparrows (Zonotrichia leucophrys nuttalli) were placed in cages with two compartments in which they could see and interact with a single social tutor. Birds were tutored with the song of their own subspecies, the song of a different subspecies, or that of an alien species, the strawberry finch (Amandava amandava). Each of the 12 birds learned the song of his social tutor. The alien song was learned even though there was abundant conspecific song present in the acoustic environment. These findings indicate that social tutoring can be effective beyond the 10–50-day sensitive phase found with tape tutoring, and that the song of an alien species can be learned from a social tutor. We conclude that neither the sensory template theory nor the current descriptions of the sensitive phase are adequate, without modification, to provide an understanding of song development in the white-crowned sparrow. Because young in the wild learn their songs from social tutors, data from studies of social tutoring provide a better basis to understand factors involved in song learning than data based on studies of tape tutoring.

Song development in the white-crowned sparrow : Social factors and sex differences

Abstract Results of earlier studies indicated that hand-raised white-crowned sparrows exposed to taperecorded songs learned conspecific song between ages 10–50 days, but not before or after that age. These studies also indicated that allospecific songs were not learned. We describe song development in 41 male and 22 female hand-raised white-crowned sparrows. Thirty males and 15 females were exposed to a live adult singing male. It was found that most male students learned the song of their live tutor even though tutoring was begun at 50 days of age, an age by which young would have dispersed from the natal to the breeding area. Male students learned allospecific song as easily as they did conspecific song, even though conspecific song was present in the laboratory. Only three females copied any part of the song of either conspecific or allospecific live tutors. Six 50-day-old males and seven females were exposed to taperecorded song and none learned the tutor song. These results indicate that there are sex differences in song learning, and that, if live tutors are used, the sensitive phase for male song learning extends beyond 50 days of age. We conclude that social interaction can override any auditory gating mechanism that prevents inappropriate stimuli from influencing song learning centres.

Song development in the white-crowned sparrow: modification of learned song

Previous research has shown that laboratory-tutored white-crowned sparrows, Zonotrichia leucophrys nuttalli, can learn tape-recorded song only until they are about 50 days of age. However, they can learn either conspecific or allospecific song after they are 50 days of age when a live tutor is used. Because the live-tutored birds had not been exposed to song during the first 50 days of life, a question regarding the reasonableness of applying these results to the natural, field situation can be raised. In the experiments reported here, hand-raised nestling white-crowned sparrows between 10 and 50 days of age were tutored in the laboratory with one song, and were then placed with a live tutor singing a different dialect when they were over 50 days of age. Eight of 13 males, and none of 10 females, adopted the song of the second tutor. Birds were also captured in the field as fledglings, and were placed with a live tutor singing a song different from that of the natal area: three of seven males, and one of five females, adopted the song of the live tutor. Four birds that had been group-isolated (two males and two females) were exposed to a live tutor when they were 100 days old, and none acquired normal song; all sang isolate song. The results of these studies indicate that there is considerable plasticity in the song learning of whitecrowned sparrows, and that, for many individuals, song can be modified quite readily. The implications of these findings for the nature of the sensitive phase and for mechanisms of song learning are discussed.

Photoperiodically induced ovarian growth in the white-crowned sparrow (Zonotrichia leucophrys gambelii) and its augmentation by song

1. 1. Ovarian growth rates were measured in White-crowned Sparrows exposed to various photoperiods and to tape-recorded male song. 2. 2. The minimum (threshold) photoperiod necessary to induce ovarian growth was slightly longer than 11L:13D. Growth rate increased linearly thereafter until the photoperiod was 16L:8D. Growth was greatest under conditions of continuous light (LL). 3. 3. The addition of song to photoperiod treatments did not affect the growth induction threshold but song did augment the rate of ovarian development when regimes were 12.5L:11.5D and 14L:10D. 4. 4. Under natural conditions song may be an important stimulus to ovarian development on both the wintering and breeding grounds.

SONG DIALECTS AS BARRIERS TO DISPERSAL: A RE-EVALUATION

Although much has been written on the subject of song dialects in birds (reviews in Thielcke, 1969; Lemon, 1975; Bitterbaum and Baptista, 1979), few data exist testing the current theories regarding the adaptive significance of these vocalizations. Two popular ideas presented by Marler and Tamura (1962) and Konishi (1965), and developed by Nottebohm (1969), are that: 1) song dialects reduce gene flow across demes by attracting birds to settle near their place of birth on hearing their familiar natal song; 2) females select males that sing their own song for mates, thus promoting deviation from panmixia. Baker (1975) and Baker and Mewaldt (1978, 1979) have tested the first using biochemical and capture/recapture techniques on sedentary White-crowned Sparrows (Zonotrichia leucophrys nuttalii). Between 1975 and 1979, we conducted a similar study on the same species at the Presidio (P) of San Francisco (see map, Fig. 1). The habitat consists of coastal soft chaparral, and is, therefore, similar to that of the Point Reyes Peninsula, 38 km to the northwest, where Baker and Mewaldt (1978) conducted their study. One might expect the local dispersal biologies of the two populations to be similar. The Presidio study area is unusual; while most birds sing the local (Presidio) dialect within the 1.5 km by 370 m area, scattered throughout this population are breeding birds singing the dialect of the adjacent San Francisco city. Additional data were gathered at a site 5.6 km south at Twin

Song Learning as Evidenced from Song Sharing in Two Hummingbird Species (Colibri coruscans and C. thalassinus)

ABSTRACr.-We have demonstrated that male hummingbirds in the genus Colibri share song types. The Sparkling Violet-ear (C. coruscans) from an Ecuadorian population and Green Violetear (C. thalassinus) from populations in Costa Rica form aggregates or neighborhoods. Males of a neighborhood sing the same song type and those of distant neighborhoods have different song types. The resultant geographic variation in song, we suggest, is due to cultural drift acquired through song learning. Song sharing was determined not only by traditional, visual examination of spectrograms of song but with a relatively new, digital cross-correlation method that permits statistical treatment. The statistical procedures included cluster analysis that reflects the distribution of songs in geographic space and an evaluation for randomness of that distribution by use of the Mantel test. Received 13 May 1993, accepted 30 September 1993.

Vocal “Dialects” in Nuttall’s White-Crowned Sparrow

The White–crowned Sparrow (Zonotrichia leucophrys) is a common breeding species on the west coast of North America, ranging from southern California to Alaska, although it is restricted to more northerly latitudes in the central and eastern part of the continent (Banks, 1964). Vocalizations of the several recognized subspecies (including Z. l. pugetensis, Z. l. oriantha, Z. l. gambelli, Z. l. leucophrys, and Z. l. nuttalli) have been examined, but it is the song of Z. l. nuttalli that has been the greatest focus of studies. Unlike the other subspecies, Z. l. nuttalli is nonmigratory and the characteristic song of the male is an ever present trademark of the coastal chapparal in central California during the summer breeding season.

Singing and its functions in female white-crowned sparrows

. Singing by female oscines is thought to be rare in north temperate latitudes. Colour-marked female white-crowned sparrows in two subspecies populations were studied: sedentary coastal Zonotrichia leucophrys nuttalli at San Francisco and migratory montane Z. l. oriantha at Tioga Pass, Sierra Nevada, California. Female Z. l. nuttalli sang regularly during the autumn, winter and early spring months prior to the onset of nesting activity. This extended period of singing during the non-breeding season suggests that female song is not an epiphenomenon related to hormonal changes just prior to the reproductive period. Females both produced spontaneous song and responded to playback with singing. Female songs differed from those of males in various frequency and temporal parameters. Female Z. l. nuttalli appeared to sing to defend territories against inserting birds-of-the-year, or to advertise for mates. A few females sang more than one song type and matched themes with mates during countersinging bouts. Females of Z. l. oriantha were observed singing in early summer upon arrival on their breeding grounds and during periods of late snow melt when nest sites were in short supply. Female songs in this subspecies were more male-like than those of the sedentary Z. l. nuttalli females. Due to the short breeding season, females of the migratory subspecies defend territories more intensely than do females of the sedentary form, which may account for the use of more male-like song in this subspecies.

SONG DEVELOPMENT AND TERRITORY ESTABLISHMENT IN NUTTALL'S WHITE-CROWNED SPARROWS

Song development and territory establishment were studied in the permanently resident Nuttalls White-crowned Sparrow (Zonotrichia leucophrys nuttalli). Hatching-year birds (juveniles) begin subsong in July, and the first crystallized songs are heard in late September. Social interaction with territorial adults accelerates song development so that song crystallizes earlier in wild juveniles than in hand-raised laboratory birds. Some juveniles begin staking out territories in September and October. At this time individuals may sing up to four song types. As time progresses settling juveniles use only one or sometimes two song types which match those of neighbors with whom they interact. Singing is performed circumannually, even during the molt in this subspecies, reflecting its year-round territo- riality.

Avian epidermal differentiation. II. Adaptive response of permeability barrier to water deprivation and replenishment.

Zebra Finches are the epitome of desert-adapted avian species; i.e. they are able to survive without drinking water for over a year. Whereas transepidermal water loss (TEWL) in naked Zebra Finch nestlings is lower than in adults, and desert adaptation is accompanied by intercellular deposition of epidermal multigranular body (MGB) contents, MGB secretion is reduced as nestlings mature into feathered adults, indicative of less stringent barrier requirements. Here, removal of drinking water resulted in increased intercellular deposition of MGB contents, and TEWL progressively decreased. In contrast, MGB intercellular deposition decreased when birds were rehydrated, with TEWL returning towards normal within 5 days of rehydration. Finally, water-deprivation caused significant changes in epidermal lipid composition that returned toward control levels with rehydration. These studies show that adult Zebra Finches adapt to xeric stress by increased secretion of multigranular bodies resulting in reduced TEWL.