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Both language and music are universal and characteristic for humans. The evolution of the cognitive abilities underlying language and music are widely debated. A core question is whether these abilities find their origins in a modification or extension of general cognitive abilities for processing auditory input also present in other species. If so, comparative studies of nonhuman animals should reveal similarities in processing abilities. In this paper, we review some examples of such studies. We focus on whether birds (in particular zebra finches, Taeniopygia guttata , and budgerigars, Melopsittacus undulates) can detect structural patterns based on relational rather than on physical similarities among auditory stimuli – an essential ability for processing and producing language and music. We briefly discuss why birds are suitable model species. Next, we discuss three domains of pattern detection: the ability to (1) detect 'grammatical rules' underlying sound strings; (2) perceive regular rhythms and (3) spontaneously group separate sounds into a larger pattern. In all of these there is evidence that birds show some ability to detect relational patterns. However, there is also variation between species: while budgerigars show relational rule learning, zebra finches attend to local physical similarities between sound strings used for training and testing. For rhythm detection, zebra finches and budgerigars show no clear differences. However, a broader comparison indicates that here too differences are present in the extent to which different bird species attend to relational patterns or to local features. Finally, spontaneous grouping of sounds was shown in zebra finches. The clear variation among bird species in their perceptual and cognitive abilities, in combination with their accessibility for experimental studies, provides opportunities to study the variation in auditory processing mechanisms and how these evolved. This may also provide hypotheses for the evolution of these abilities in humans. • The evolution of the cognitive mechanisms underlying music and language is debated. • Comparative studies in birds provide insights in the evolution of these mechanisms. • Some species can learn grammatic rules, perceive rhythm and show perceptual grouping. • Interspecific variation provides a tool to study how mechanisms and variation evolve. [ABSTRACT FROM AUTHOR]

It has been proposed that leks arise because of increased mating benefits in aggregations of displaying males, and some evidence supports this hypothesis. But observations also indicate that lekking aggregations include only a small percentage of the males in a population, implying that certain factors limit lek size. Potential factors include increasing travel costs to find and form large but distant aggregations, greater attraction of predators and higher levels of aggression. Any one of these constraints may cause the number of females arriving at larger leks to decelerate such that per capita male attractiveness, and hence mating success, declines above an optimum lek size. None the less, relatively little empirical work has examined what determines lek size. In particular the possibility that cognitive aspects might constrain lek size has rarely been considered. We studied this question in Achroia grisella , an acoustic moth in which singing males form small aggregations that attract females. We created artificial leks in the laboratory and tested their relative attractiveness to females; we also tested male preferences to form and join such aggregations. Females preferred male aggregations over solitary singers, but the marginal per capita attractiveness of an aggregation of n + 2 males versus n males waned for n ≥ 5. Similarly we found that males were attracted to other males singing in the vicinity, but this effect disappeared for n ≥ 4. We infer that lek size is limited because the marginal per capita attractiveness of larger leks only occurs for small groups. This constraint probably arises because females distinguish leks by overall song rate but are neuroethologically incapable of discriminating rates above a threshold value corresponding to groups of four to six males. These findings emphasize the critical role that neural constraints may play in determining fundamental parameters of complex behaviours such as lekking. [ABSTRACT FROM AUTHOR]