Song production in song birds is controlled by an efferent pathway. Appended to this pathway is a “recursive loop” that is necessary for song acquisition but not for the production of learned song. Since zebra finches learn their song by imitating external models, we speculated that the importance of the recursive loop for learning might derive from its processing of auditory feedback during song acquisition. This hypothesis was tested by comparing the effects on song in birds deafened early in life and birds with early lesions in either of two nuclei--Area X and the lateral magnocellular nucleus of the anterior neostriatum (LMAN). These nuclei are part of the recursive loop. The three treatments affected song development differently, as reflected by various parameters of the adult song of these birds. Whereas LMAN lesions resulted in songs with monotonous repetitions of a single note complex, songs of Area X-lesioned birds consisted of rambling series of unusually long and variable notes. Furthermore, whereas song of LMAN lesioned birds stabilized early, song stability as seen in intact birds was never achieved in Area X-lesioned birds. Early deafness also resulted in poorly structured and unstable song. We conclude that Area X and LMAN contribute differently to song acquisition: the song variability that is typical of vocal development persists following early deafness or lesions of Area X but ends abruptly following removal of LMAN. Apparently, LMAN plays a crucial role in fostering the kinds of circuit plasticity necessary for learning.

https://www.jneurosci.org/content/jneuro/11/9/2896.full.pdf

A comparative study of the behavioral deficits following lesions of various parts of the zebra finch song system: implications for vocal learning.

This review examines how birds use the annual cycle in photoperiod to ensure that seasonal events—breeding, molt, and song production—happen at the appropriate time of year. Differences in breeding strategies between birds and mammals reflect basic differences in biology. Avian breeding seasons tend to be of shorter duration and more asymmetric with respect to changes in photoperiod. Breeding seasons can occur at the same time each year (predictable) or at different times (opportunistic), depending on the food resource. In all cases, there is evidence for involvement of photoperiodic control, nonphotoperiodic control, and endogenous circannual rhythmicity. In predictable breeders (most nontropical species), photoperiod is the predominant proximate factor. Increasing photoperiods of spring stimulate secretion of gonadotropin-releasing hormone (GnRH) and consequent gonadal maturation. However, breeding ends before the return of short photoperiods. This is the consequence of a second effect of long photoperi...

Photoperiodic Control of Seasonality in Birds

Aim We reviewed the occurrence of Bergmann’s rule in birds (ninety-four species) and mammals (149 species), using only studies where statistical significance of the results was tested. We also tested whether studies using different characters as surrogates of body size have a different tendency to conform to Bergmann’s rule, whether body size and nest type (in birds) have an influence on the tendency to conform to the rule, and whether sedentary birds conform to the rule more than migratory birds. Location Worldwide. Methods We reviewed published data on geographic and temporal variation in body size, using only studies where the statistical significance of the results was tested. We asked how many species conform to the rule out of all species studied in each order and family. Results Over 72% of the birds and 65% of the mammal species follow Bergmann’s rule. An overall tendency to follow the rule occurs also within orders and families. Studies using body mass in mammals show the greatest tendency to adhere to Bergmann’s rule (linear measurements and dental measurements show a weaker tendency); while in birds, studies using body mass and other surrogates (linear measurements and egg size) show a similar tendency. Birds of different body mass categories exhibit a similar tendency to follow Bergmann’s rule, while in mammals the lower body size categories (4–50 and 50– 500 g) show a significantly lower tendency to conform to the rule. Sedentary birds tend to conform to Bergmann’s rule more than migratory species. Nest type does not affect the tendency to conform to Bergmann’s rule. Main conclusions Bergmann’s rule is a valid ecological generalization for birds and mammals.

/pdf/on-the-validity-of-bergmann-s-rule-sf29n9xsn5.pdf

On the validity of Bergmann's rule

EXTRA-PAIR copulations (EPCs) seem to be one of the most widespread alternative reproductive behaviours by which male birds can increase their fitness1,2. In many species females actively solicit or freely engage in EPCs3–5, which suggests that they benefit from them. Of the eight hypothetical benefits proposed2,6, the most likely are genetic2. Often females engage in EPCs with more dominant males3,7 or with males with more elaborate ornaments8,9. In species in which paternity was assigned, extra-pair young were divided asymmetrically between males10–12. Here, combining detailed behavioural work with DNA-fingerprinting of an entire population, we present evidence that such an asymmetry is indeed caused by female behaviour, and that 'attractive' males do not suffer lost paternity, survive better and recruit more young. Our results support the genetic quality hypothesis.

Extra-pair paternity results from female preference for high-quality males in the blue tit.

Two timely evolutionary issues concern the potential for sexual selection in mating systems characterized by substantial parental investment by both sexes and the occurrence and significance of mate preferences for aesthetic characteristics. Here F explore these issues at their interface. First, I hypothesize two processes that may generate differential reproductive success (RS) resulting from the possession of aesthetic traits in species with parental investment (PI) by both sexes. The differential-access hypothesis posits that attractive individuals have preferential access to high-quality mates. The differential-allocation hypothesis states that mates of attractive individuals are "willing" to contribute greater than average PI to obtain and/or maintain their attractive mates. Second, I report on experiments that investigate the impact of aesthetic traits on fitness (long-term RS). The test organism is the zebra finch (Poephila glittata), a sexually dimorphic, typically monogamous estrildid. The aesthetic traits are plastic leg bands of various colors. Previous research has shown that zebra finches prefer oppositesex adults wearing certain colors (attractive traits) and avoid those wearing other colors (unattractive traits).

Sexual Selection for Aesthetic Traits in Species with Biparental Care

The frequency of extra-pair parentage in a wild population of zebra finches Taeniopygia guttata was examined by DNA fingerprinting. A total of 25 families, comprising 16 pairs of parents and 92 offspring (in broods of 1 to 6) were examined. Ten cases of extra-pair parentage, presumed to constitute intraspecific brood parasitism, were detected (10.9% of offspring or 36% of broods), including one possible instance of ‘quasi-parasitism’ (parasitism by a female fertilized by the male nest owner). The average number of parasitic eggs per clutch detected by fingerprinting was 1.10±0.32 SD, very similar to the one egg difference in average clutch size between parasitised (6.0±0.82) and unparasitised nests (5.0±0.95). Two cases of extra-pair paternity (EPP) were detected among 82 offspring whose maternity was confirmed: 2.4% of offspring, or 8% of broods. In both cases EPP accounted for only a single offspring within a brood. Behavioural observations show that EPP occurs through extra-pair copulation rather than rapid mate switching. The results are discussed in the light of what is known about the fertile period and sperm precedence patterns in this species.

https://www.jstor.org/stable/pdfplus/4600485.pdf

Extra-pair paternity and intraspecific brood parasitism in wild zebra finches Taeniopygia guttata, revealed by DNA fingerprinting

Zebra Finches Taeniopygia guttata are renowned for breeding opportunistically in arid Australia and for their ability to nest immediately in response to rain at any time of year. However, this conclusion has rested on short-term and incidental observations. We monitored breeding of Zebra Finches at Alice Springs, central Australia, over a seven-year period by estimating the month of hatching of free-flying subadults caught at a walk-in trap. Capture-mark-recapture analysis suggested that the monitored population was open and highly mobile and exploited a large home range. Despite gaps in the sampling a multiple regression analysis found a significant statistical relationship between breeding and the incidence of rainfall. When conditions were favourable in a given year Zebra Finches had a very long reproductive period with 10.6 equally good consecutive months for breeding. Breeding was possible in every month of the year but was least in April and greatest n October. Low winter temperatures did not prevent breeding. The heavier the rainfall, the more intense and the longer the breeding episode. Once a breeding episode began, surges of breeding activity corresponded with follow-up rains. We did not observe the immediate response to rainfall described by earlier authors. On the contrary, the statistical analysis revealed that rain had a negative effect on breeding in the month in which it fell, and in the following month. There was a lag between the onset of the first rains and the onset of breeding, ranging from one to two months in summer to two to three months in winter. The statistical analysis revealed that rain four months previously had the most profound positive effect on breeding. Hatching of the first clutches coincided with the first availability of ripening grass seeds. The artificial supply of abundant dry seed, on its own, did not stimulate breeding. The timing of seed set by grasses in central Australia is complex, depending on the species composition, the prevailing temperatures immediately after rain, and the amount and timing of previous falls of rain. We suggest that Zebra Finches track these factors and breed opportunistically as soon as new supplies of seed are available.

The Timing of Breeding by Zebra Finches in Relation to Rainfall in Central Australia

We investigated song development in the pre-independent zebra finch (aged 15-35 d), a period when neural pathways for song learning and production are forming and social influences outside the family are limited. Expt 1 investigated the onset and the minimum duration of tutoring needed for song learning in fledglings. We found most begin to learn song from 25 d of age and need about 10 d contact with the father tutor to make accurate copies. This onset corresponds with major developments in the formation of the neural circuitry implicated in song acquisition. Subsong also begins on day 25 suggesting that the sensory and motor phases of song learning fully overlap in the zebra finch. Our findings support the hypothesis that the song circuitry is fully functional by 35 d of age and the sensitive phase for zebra finches extends therefore from about days 25-65. However, only the first 10 d of this period are necessary to learn a tutor's song with fair accuracy. Expt 2 investigated the role of the paternal bond, spatial proximity and mating status in a fledgling's choice of song tutor where the father was the sole parent. Young chose the father over single unrelated males (expt 2a) or unrelated males in company with their female partners (expt 2b). Given the close spatial proximity of both potential tutors to the fledglings it is probably the filial bond, established via paternal care that is the cause of this preference. Zebra finches sing the same song phrase in two contrasting contexts: female-directed song during pre-copulatory courtship and undirected song where no female or display is involved. In expt 3 we tested the song learning preference of pre-independent young for two categories of non-paternal tutors: those singing predominantly female-directed song and those singing exclusively undirected song. There was a small, but significant, preference for fledgling zebra finches to copy songs from males that sang female-directed song. This preference is consistent with the hypothesis that young males not only learn the acoustic features of their tutor's song but also the visual and dynamic movements that constitute the courtship display.

The Onset of Song Learning and Song Tutor Selection in Fledgling Zebra Finches

Song and call learning in wild zebra finches in south-east Australia

Summary


1
Opportunistic breeding (i.e. breeding whenever favourable conditions occur, regardless of interval or periodicity) is a strategy often adopted by animals breeding in habitats where food resources important for offspring survival are unpredictable.

2
One putative adaptation for this breeding strategy is the maintenance of a partially activated reproductive system year-round. Breeding readiness is assumed to be the default state and reproduction is therefore suppressed only when environmental conditions become inhibitory.

3
We tested this assumption in an opportunistic archetype, the Australian zebra finch Taeniopygia guttata, by comparing reproductive activation and suppression in free-living zebra finches in two climatically different habitats: (1) an unpredictable habitat of arid central Australia, where breeding is closely tied to aperiodic rainfall and can occur during any month of the year, and (2) a more predictably seasonal habitat in southern Australia, where breeding occurs during approximately the same months each year. We quantified reproductive activation by measuring gonad size and circulating gonadotrophin concentration during the breeding and nonbreeding seasons in the predictable habitat and within a nonbreeding period during drought in the unpredictable habitat.

4
We found reproductive readiness changed consistently between the breeding and nonbreeding state in the predictable habitat, but more nonbreeding birds in the unpredictable habitat maintained an activated reproductive system even though they had poorer body condition. We found no evidence for suppression of reproductive activity by stress hormones (i.e. elevated glucocorticoids). Furthermore, birds were able to activate the reproductive axis quickly when removed from inhibitory field conditions and responded equally well to various stimulatory cues.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2006.01237.x

Richard Zann

Papers

Extra-pair paternity and intraspecific brood parasitism in wild zebra finches Taeniopygia guttata, revealed by DNA fingerprinting

The Timing of Breeding by Zebra Finches in Relation to Rainfall in Central Australia

The Onset of Song Learning and Song Tutor Selection in Fledgling Zebra Finches

Song and call learning in wild zebra finches in south-east Australia

Opportunism at work: habitat predictability affects reproductive readiness in free‐living zebra finches