Chapter 9 Opener: When a bull elk bugles, other males listen

9.1 The pseudopenis of the female spotted hyena can be erected

9.2 Concentrations of testosterone in male and female spotted hyenas (Part 1)

9.2 Concentrations of testosterone in male and female spotted hyenas (Part 2)

9.3 A cost of the pseudopenis for female spotted hyenas

9.4 Competition for food among spotted hyenas may favor highly aggressive individuals

9.5 Dominance greatly advances female reproductive success in the spotted hyena

9.6 Ultrasonic communication

9.7 Evolution of a sensory system

9.8 Arthropod gills have evolved into many different structures with different functions (Part 1)

9.8 Arthropod gills have evolved into many different structures with different functions (Part 2)

9.9 Evolutionary precursors of insect wings?

9.10 A surface-skimming stonefly

9.11 A possible evolutionary pathway from swimming to full flight in the stoneflies

9.12 An ancestral signal has been co-opted in some bowerbirds

9.13 Sensory exploitation and the evolution of a courtship signal in Neumania papillator

9.14 Two evolutionary scenarios for the evolution of male courtship trembling in Koenikea (Part 1)

9.14 Two evolutionary scenarios for the evolution of male courtship trembling in Koenikea (Part 2)

9.15 A female cichlid fish (left) is attracted to the anal fin of a male by the orange spots on the fin

9.16 Food, carotenoids, and female mate preferences in the guppy

9.17 Sexual preferences for orange spots match foraging preferences by female guppies

9.18 The response of least auklets to three novel artificial signals

9.19 Receivers can respond to an ancestral signal not present in their species

9.20 Sensory exploitation and swordtail phylogeny

9.21 Mate preferences for a novel ornament

9.22 The panda principle is evident in the sexual behavior of a parthenogenetic whiptail lizard

9.23 A group of ravens feeding on a carcass to which they were attracted by a yelling companion

9.24 Yelling is a recruitment signal

9.25 Predation risk has affected the evolution of begging calls in warblers (Part 1)

9.25 Predation risk has affected the evolution of begging calls in warblers (Part 2)

9.26 Testosterone affects begging rate and feeding rate in black-headed gull chicks

9.27 An honest signal of hunger?

9.28 The European cuckoo chick’s begging call matches that of four baby reed warblers (Part 1)

9.28 The European cuckoo chick’s begging call matches that of four baby reed warblers (Part 2)

9.29 The cuckoo’s begging calls stimulate more frequent feeding by its host parents

9.30 Illegitimate receivers can detect the signals of their prey (Part 1)

9.30 Illegitimate receivers can detect the signals of their prey (Part 2)

9.31 Great tit alarm calls

9.32 Hearing abilities of a predator and its prey

9.33 Convergent evolution in a signal

9.34 Deep croaks deter rivals

9.35 Threat displays are energetically demanding in the side-blotched lizard (Part 1)

9.35 Threat displays are energetically demanding in the side-blotched lizard (Part 2)

9.36 Convergent threat displays

9.37 Antler span in two New Guinean fly species provides accurate information about body size

9.38 An honest signal

9.39 A firefly femme fatale

9.40 A deceptive signaler