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                                                             Matt Johnson
                                                          HSU Wildlife 365
                                                              Ornithology

                         ORNITHOLOGY
                (Humboldt State Univ. WILDLIFE 365)

            LECTURE 15 – VISUAL COMMUNICATION


I.     Introduction – birds communicate with each other and other animals
       with displays – vocal and/or visual. These displays transmit
       information from the birds (sender) to some other animal (receiver),
       which may be a potential mate, a rival, or a predator. Today’s
       lecture is on visual displays.
II.    Plumage Color. A primary mode of visual display in birds is by way
       of plumage color……
       A. Cryptic coloration…..and the principal “display” performed by
           coloration is to be inconspicuous. Cryptic coloration is animal
           camouflage. And in birds it is well developed in some species.
           Some examples:
           1. Female Eider.
           2. Others. -- common potoo (posture and plumage)
           3. Disruptive coloration – Killdeer.
           4. Countershading – basic plumage Dunlin.
       B. Other plumage coloration.
           1. Reverse countershading – alternate Dunlin.
           2. Uniform coloration is conspicuous to signal to conspecifics–
               Mt. Bluebird/Cardinal.
           3. Contrast edges enhance signal patches – Hooded
               Merganser/Hooded Oriole.
III.   How birds ID themselves.
       A. You think you have it hard IDing all these birds! Think about a
           young Herring Gull in a winter mixed flock of California,
           Western, Herring, and Glaucous-winged Gulls, all ages, all
           sexes….determining who is who is no easy task. Actually, as
           you might have guessed, birds are profoundly better at
           distinguishing subtle differences in behavior that reveal a bird’s
           species, age, and sex than we can ever dream of being. They
           don’t need field guides. Nonetheless, there DO appear to be
           some adaptations in birds to make species, age, and sex very
           obvious in some cases.
       B. Sexual differences in coloration usually reflect inequalities in
           selection pressure based on different roles in reproduction (males
           attract mates, females incubate): males are selected for bright,
           attractive colors to maximize probability of breeding. Females
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   are selected to minimize predation risk. This pattern varies as
   you’d expect when reproductive roles vary: species in which
   both sexes incubate (Ash-thr. Flyc.) are sexually monomorphic.
   Species in which females attract mates and males incubate show
   bright females and dull males (Wilson’s Phalarope). We’ll talk
   more about this in a bit when I talk about sexual selection.
C. Delayed plumage maturation – many birds have different
   plumages as young than as adult birds. These immature
   plumages are often more cryptic than adult plumages, but not
   always. These have evolved at least partly to maximize cryptic
   coloration. The obvious reason is to reduce risk of predation.
   But many immature birds are subordinate, so it also behooves
   them to be inconspicuous to dominant conspecifics. Also, many
   immature male songbirds fail to attract mates to a defendable
   territory. However, they still attempt some breeding by
   “sneaking” copulations with already paired females. Their
   cryptic coloration is multipurpose indeed. Redstart slides.
   1. Why delayed plumage maturation? 4 ideas: using cost-
       benefit analysis (these are not mutually exclusive).
   2. Cost of course is reduced reproductive success. These birds
       do NOT attain adult breeding plumage which has evolved for
       successful mate attraction. Instead, they remain cryptic. So
       what might be the benefits of remaining cryptic for an extra
       year (these benefit must outweigh the cost or this molt
       sequence would be purged from the population via natural
       selection.)
   3. First, the benefit could be enhanced survival simply because
       risk if predation on a cryptic bird is less than on a bright
       plumaged bird. This would be especially advantageous for
       long-lived bird species, because they could then reap the
       benefits of early survival for many years down the line.
       Thus, early survival contributes more to lifetime reproductive
       success for long-lived the short-lived species. We’ll talk
       more about LRS in a couple of weeks.
   4. Second, the benefit could be a reduced energy expenditure
       for growing brown (energetically cheap) feathers rather than
       bright (energetically expensive) feathers.
   5. Or, there could be more subtle benefits. For many birds,
       their likelihood of reproducing successfully in their first year
       is poor (regardless of plumage) because of their lack of
       experience. Thus, they are in a bad situation, and perhaps
       delayed plumage maturation has evolved simply to make the
       best of an already bad situation. Two hypotheses in this line
       of thinking.
   6. Third, a dull plumage could reduce intra-specific
       competition from breeding adults (e.g., males) by sending the
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                plumage signal that the dull bird is in its first year and thus
                less of threat than other adult birds. The cryptic plumage
                could tell other adults, “I’m a pee-on, don’t pick on me.”
            7. Fourth, birds (especially males) in their first year of life may
                be unlikely to successfully breed on their own. But as we
                study birds that we previously thought were largely
                monogamous more and more, we’re gradually learning that
                there is a lot more “extra-pair copulations” out there than we
                previously thought. A female-like plumage may increase an
                immature birds chances of obtaining “sneak copulations”
                with other females because they will both more
                inconspicuous and less imposing to adult males than if they
                were to be adorned with bright adult breeding plumages.
        D. Individual recognition. Redstart overhead? (not covered)
IV.     Evolution of displays. In text, see Pelicaniformes and Manakins.
V.      Rituals.
        A. What are rituals? – Ritualization is the evolution of stereotyped
            signals and displays from “normal behavior” movements. For
            example, a bird pecking another bird is clearly sending a signal,
            but it is not a ritual, it is real. A bird that cocks its head as if to
            peck another is sending a signal via a ritual whether or nor that
            behavior is actually ever followed by a peck.
        B. From where do they originate? Rituals usually develop from
            incomplete locomotor movements – called intention movements.
            For example the head-throw display of courting male Common
            Goldeneyes probably evolved from the initial movements
            associated with leaping out of the water. OVERHEAD
        C. Why do they evolve?
            1. To increase efficiency of communication. Much information
                can be transferred without going through entire motions.
            2. To increase clarity of intent. Rituals are usually very
                stereotyped, this is, they don’t vary much. They are often all-
                or-nothing. This makes them clear.
            3. Graded displays. But some are in fact, graded. But these still
                may communicate information clearly. Steller’s Jay crests
                OVERHEAD.
VI.     What do displays mean?
 Deciphering the information transferred in behaviors is a huge challenge
    in ornithology.
 Often, a single display can vary in subtle ways with dramatic changes in
    purpose. Crouch in female redstarts (submission posture for breeding) --
    vs. wing droop (aggressive posture between males).
VII. Agonistic behavior.
        A. When two birds interact, it is important to remember that each
            individual has selfish purposes that can foster either hostility or
            cooperation. A male bringing food to a female looks “nice” but
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   we all know why he does it. Other examples abound in nature of
   cooperative behaviors that clearly confer advantage on both
   participants. Thus these behaviors are, at their core, selfish
   behaviors.
B. In this light, the nature of interactions between rivals and
   partners are especially interesting.
   1. Rivals. Competitive encounters are complex mixtures of
       aggressive (threat and attack) and submissive (submit, flee)
       displays. These are called agonistic interactions.
       a. Threat displays usually mimic initial attack movements,
            and they serve to transmit intent while diminishing risk of
            injury to both parties.
       b. Threatening birds usually sleek their postures and look
            directly at the other bird, submissive birds often fluff-up
            their feathers and turn away.
   2. Partners. Interactions between sexes often start agonistically.
       Males are aggressive toward female – if she does not flee,
       she sends the signal that this interaction is not a rival
       interaction, and her/his displays usually shift from hostility to
       appeasement, to mutual subordination, and to solicitation.
       Then they form their bond.
C. For years biologists assumed rituals evolved for clarity –
   meaning they were “true.” But it is becoming increasingly clear
   that many times, birds are being deceitful. They bluff, they even
   act like females when they are males. Escape signals are usually
   more reliable. It’s the aggressors that are often fibbing.
   1. It’s been demonstrated that a purely “honest” signaling bird
       society is not a so-called “evolutionarily stable strategy.”
       That is, if one bird began to cheat by bluffing (e.g., acting
       like it was the strongest bird in the group but was in fact one
       of the weakest) it would obtain a disproportionate amount of
       resources because the other birds would react subordinately
       to its displays, even though many of them may be stronger.
       Thus, this “cheater” or “bluffer” strategy would be more
       evolutionarily successful than the honest strategy and it
       would proliferate in the population.
   2. Ah, but a society of all cheaters is not stable either.
   3. In the end, what IS stable is a bird society made up primarily
       of honest signalers, with a equilibrium reached between a
       smaller number of “cheaters or bluffers” (those that display
       dishonestly) and “checkers or callers” (those that will test a
       display regardless of its intensity).
   4. How surprising is that? Not very. Our own societies (and in
       fact even in ourselves) work the same way. Most people are
       relatively honest, a few cheat, and a few are paranoid
       (thinking everyone is cheating). It’s stable.
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VIII.   Sexual selection
        A. Dramatic differences between male and female plumage and size
           are commonplace in birds. A few of these may result from real
           differences in their ecologies, but most result from what Darwin
           called “sexual selection.”
        B. Sexual selection is evolutionary pressure stemming from contests
           among males (usually) for mates and among females (usually)
           for preferences for particular traits in mates. Easiest to see in
           polygynous birds.
        C. Females, generally, are much more “choosy” than males. This is
           because, ultimately, they have more invested per reproductive
           event because female sex cells (eggs) are larger, more
           energetically costly, and therefore more rare and valuable than
           male sex cells (sperm). Thus, females have more at risk in a
           particular reproductive event -- their evolution favors quality
           over quantity; males favor quantity over quality.
        D. The result is that males usually compete for mates, whereas
           females do less so; and therefore males’ reproductive success
           varies more than does females (especially for non-monogamous
           mating systems).
        E. Thus, traits that enhance a male’s ability to attract a mate are
           quickly and efficiently selected – often to extreme ends.
        F. Examples.
           1. Red-wing Blackbirds.
               a. Females choose mates based on the quality of the
                   territories they defend.
               b. Males that had their epaulettes experimentally blackened
                   get attacked more often than control males, and usually
                   lost their territories (and reproductive potential). Those
                   that did manage to retain their territories still bred. Thus,
                   the epaulettes were important signals to rival males, but
                   were unimportant to females (they were interested in the
                   territories). This is still sexual selection because the
                   epaulettes serve no purpose other than to maximize
                   reproductive output by indirectly procuring mates.
           2. Long-tailed Widowbird.
               a. They are marsh birds like the red-wings.
               b. But here, evolution has favored the extension of the tail.
                   Experimental manipulations have demonstrated that birds
                   with short tails attract fewer females. OVERHEAD
           3. Bowerbirds.
               a. The most elaborate sexual selection of all is perhaps in
                   the Bowerbirds of Australia/New Guinea. OVERHEAD
               b. Males construct elaborate displays of sticks, shells, parrot
                   feathers, etc. to attract females.
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       c. The duller the male (by species) the more elaborate the
          bower.
       d. Females clearly choose the most well-maintained
          decorative bowers.
       e. This probably serves as an accurate indicator of a male’s
          vigor, because it takes considerable effort to collect,
          defend, and/or pilfer the items. Only a male adept at
          gaining food and avoiding predation can manage the time
          and energy for the most impressive bower.
G. Good genes vs. fashion icons. -- This brings up the idea of what
   sexual selection really signals to females. Two hypotheses exist
   (not mutually exclusive)
   1. Good Genes.
       a. Some displays are best performed by superior (strong
          etc.) males. Thus, the best performer is probably very fit.
       b. Other sexual characteristics may signal fitness by serving
          as “handicaps.” Having an extremely long tail or very
          conspicuously bright plumage but still being alive may
          signal that the male is adept at avoiding predation or
          obtaining enough food to enable rapid feather growth.
   2. Arbitrary choice (fashion icon).
       a. These may often start as signals for good genes. But if
          for some reason…any reason…females just prefer longer
          and longer tails, then only males with long tails will
          reproduce and the pattern will be perpetuated.
       b. This may be the case for extreme sexual
          plumages/displays such as those found in the birds of
          paradise. SLIDE