Feb 26: Song Dialects: Birds. Why Do Birds Sing?

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Joan Adams
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1 Feb 26: Song Dialects: Birds Why Do Birds Sing? Why this is an ill-posed question need to specify the correct level of analysis (for now, we are referring to the functional question of survival value) even considering it as a functional question, it is TOO GENERAL Three more specific questions about bird song Why do different species sing different songs? Why do only males sing (usually)? Are dialects (interpopulation variation within a species) adaptive?

functional question of survival value) even considering it as a functional question, it is TOO GENERAL Three more

2 Feb 26: Bird Song Dialects: Digression A Functional Perspective on Communication What communication is--a broad definition: Production of signals by one individual (sender) that change the behavior of other animals (receivers) This broad definition is TOO broad Includes signals that change the behavior of receivers to the benefit of the receiver but to the detriment of the sender (e.g., the rustling of a mouse that attracts a predator) Natural selection would not favor traits in sender that work against the interests of the sender (there is no "function" of the mouse's rustling) A narrower definition: Production of signals by one individual that change the behavior of a receiver in a way that benefits the sender This type of communication need not only occur among members of the same species Also, the receiver might also benefit by having changed its behavior in response to the signal Thus, a rattlesnake's rattle signals to potential predators that the snake is dangerous (this is good for the snake as well as for the would-be predator)

3 Feb 26: Bird song dialects: Why do different species sing different songs? Why Do Different Species Sing Different Songs? H1: Songs diverge by chance (genetic drift) after speciation (perhaps associated with selection for consistency within species) Most likely hypothesis for most species H2: perhaps differences reflect adaptation to different local conditions (e.g., different acoustical environments Some evidence of this in Great Tits (in Europe)--woodland populations have lower frequency songs than grassland populations H3: Selection for divergence of traits involved in species recognition--to prevent hybridization No evidence for more pronounced song differences in indigo and lazuli buntings where their ranges overlap (in Nebraska)

differences reflect adaptation to different local conditions (e.g.

4 Feb 26: Bird song dialects--why only males? Why Do Only Males Sing? H1: Tendency of males to sing (and females to not sing) is side-effect of sexual differentiation of reproductive behavior H2: Song involves costs (time, energy, exposure to predators); Perhaps only the males reap benefits of singing in most species

sexual differentiation of reproductive behavior H2: Song involves costs (time,

5 Feb 26: Bird song dialects--why only males? Why Do Only Males Sing? (cont d) Hypothesis 2a: Males benefit by attracting females Choosy females use song as indicator of male quality (we postpone for now the question of why females tend to be the choosy sex--see Chap. 12) Evidence: In many species, males sing only when trying to attract mates In many species, females clearly choose among males based on song--e.g., song complexity In starlings, males with larger song repertoires are chosen earlier, and have young earlier Alcock Fig. 8.3

the question of why females tend to be the choosy sex--see Chap.

6 Feb 26: Bird song dialects--why only males? Why Do Only Males Sing? (cont d) Hypothesis 2b: Males benefit by more effectively repulsing rival males Female is a resource for which males compete Any trait that enhances competitiveness would be favored Perhaps songs serve to warn other males of presence and quality of singer Evidence: In some species, males sing most when mates are fertile, hence when male has most to lose by intrusion of rival male In white-throated sparrows, removal of singing male results in intrusion by rival, but tape recording delays intrusion In starlings, recordings of complex songs are more effective than recordings of simple songs; thus, in starlings, song complexity has survival value for both mate attraction and rival repulsion Alcock Fig. 8.4

songs serve to warn other males of presence and quality of singer Evidence: In some species, males sing most when mates are fertile, hence when male has most to lose by intrusion of rival male

7 Feb 26: Bird song dialects--are dialects adaptive? Are Dialects Adaptive? H1: NO--they result from non-adaptive genetic or cultural drift? In indigo buntings, dialects do drift around over time--doesn t mean they are non-adaptive H2: YES--perhaps they represent adaptation to local physical environment Scant evidence of this H3: YES--perhaps they represent adaptation to local social environment

In indigo buntings, dialects do drift around over time--doesn t mean they are non-adaptive H2:

8 Feb 26: Bird song dialects--are dialects adaptive? Are Dialects Adaptive? - cont d H3a: Dialects are adaptive through process of female choice: perhaps females prefer to mate with male who sings like Dad (hence are adapted to same environment in which Dad was successful) Evidence: In brown-headed cowbirds, females do prefer to mate with males singing their own dialect However, ability of males to change dialect over lifetime (e.g. white-crowned sparrow) means that dialect doesn t predict place of birth H3b: Dialects are adaptive through process of rival repulsion: perhaps males are more effective in repelling rivals if they can talk the talk --indicates familiarity with habitat, staying power Song-matching in song sparrows Alcock Fig. 8.7

successful) Evidence: In brown-headed cowbirds, females do prefer to mate with males singi

9 Feb 26: Song Dialects: Birds Why Do Birds Sing? Three more specific questions about bird song Why do different species sing different songs? Apparently a combination of selection for species recognition and drift Why do only males sing? Intersexual selection (mate attraction) & Intrasexual selection (rival repulsion) Are dialects (interpopulation variation within a species) adaptive? Differences may be useful in indicating familiarity with local neighborhood

Apparently a combination of selection for species recognition and drift Why do only males sing?

Biology 1406 - Notes for exam 5 - Population genetics Ch 13, 14, 15

Biology 1406 - Notes for exam 5 - Population genetics Ch 13, 14, 15 Species - group of individuals that are capable of interbreeding and producing fertile offspring; genetically similar 13.7, 14.2 Population