PSY 2364 Animal Communication. Courtship and mating systems. Mating systems. Mating systems. Mating systems. Mating systems 11/12/2018

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1 PSY 2364 Animal Communication Courtship and mating systems Mating system refers to the extent and manner in which males and females associate during mating. Mating systems Monogamy One male mates with one female Polygyny One male mates with more than one female Polyandry One female mates with more than one males Polygynandry More than one male, more than one female Mating systems Monogamy One male mates with one female Most common reproductive system in birds (90%) Relationship to habitat quality (sparseness or abundance of resources) Mating systems Polygyny One male mates with more than one female Overall this is the most widespread mating system in the animal kingdom (e.g., lions, deer, horses, ) Why? Mating systems Polyandry One female mates with more than one male Relatively rare (1% of all bird species; Jacana, Phalaropes) Often associated with reverse pattern of sexual dimorphism (female is larger or more showy than the male) 1

2 Anisogamy Sex cells (gametes) differ in size and quantity in males and females Female produces larger reproductive cells (eggs) Males produce a greater quantity of smaller reproductive cells (sperm) Parental investment is unequal Anisogamy This difference is especially pronounced in birds Females produce relatively few eggs; limited number of offspring Survival depends on successful mate choice Males invest less to produce a single embryo Natural selection favors strategies that maximize the number of offspring Therefore males should be less discriminating and attempt to mate as often as possible Mating with a less fit partner has a smaller impact on males than females Lek formation Lek: small arena where males set up and defend a temporary territory specifically for mating. Females approach the lek and select a mate from the males that are present. Sometimes a single male is responsible for a large (>80%) proportion of all matings (polygyny). Common Raven (Corvus corax) Kingdom: Animalia Phylum: Chordata Class: Aves Order: Passeriformes Family: Corvidae Genus: Corvus Species: Corvus corax World s largest passerine Heinrich (1989). Ravens in winter. Ravens have a large repertoire of sounds. Yelling sound made by ravens when feeding on the carcass of a moose or deer in winter. Yelling sounds like a dog whose tail has been caught in a slammed door. 2

3 A raven yelling can be heard up to a mile away on a clear winter day. Ravens use this call only when they find a rich and scarce food source (carcass of a dead animal, like a moose or deer in winter). Yelling attracts other ravens to the carcass. Why do ravens yell? Why attract competitors when food is scarce? Maybe yelling helps the group as a whole (group selection account)? Maybe yelling attracts family members (kin selection account)? Maybe yelling helps the individual somehow? Ravens yell more when they are hungry. If yelling is directed at family members, then most of the members of the flock should be related. Heinrich found up to 15 ravens at a single carcass, but raven families produce at most six offspring in the breeding season. Later, genetic fingerprinting confirmed that most members of the flock were unrelated individuals. Could yelling be directed at other predators, like coyotes or bears, who could open the tough-skinned carcass of a dead moose? No: ravens do not always yell when they find a carcass. Sometimes they yell even when the carcass is already ripped open. Does yelling dilute the risk of predation for an individual bird by attracting others? No, because ravens continue to yell even after the flock has reached its largest size. 3

4 Does yelling provide a benefit for ravens who are not members of the resident, territorial group? Adult ravens maintain year-round territories. Non-resident wanderers (unmated young birds) are driven out by resident, territorial birds Yelling might be a strategy to attract other nonresidents to gang up on the residents. Gang-up-on-territorial-residents hypothesis Resident territory owners never yell Non-resident, non-territory holders yell Yelling attracts other non-residents to the carcass Residents are unable to drive off non-residents Gang-up-on-territorial-residents hypothesis Ravens at a carcass are either (1) a small group of exclusively residents or (2) a large flock of residents + non-residents. Mobile roosts as information centers Marzluff and Heinrich (1996) reported that ravens form temporary roosts near newly discovered food sources (a large animal carcass). Hypothesis: these mobile roosts serve as information centers to provide roost-mates with the opportunity to share their knowledge of food sources. Mobile roosts as information centers Marzluff and Heinrich (1996) found that roosts contained both informed and naïve individuals. But every morning the entire flock tended to go in the same direction. The synchronized behavior suggests they had communicated about the food source. Mobile roosts as information centers Are the informed ravens leading the group? When captured (naïve) ravens were allowed to rejoin the group they always followed the others. When captured ravens were given knowledge of new food sources (by releasing them at new carcasses) they joined roosts and sometimes led the others to the food source. 4

5 Mobile roosts as information centers The same individual would act as a leader when provided with knowledge of a new food source, and as a follower when it was denied knowledge that other birds in the roost knew. Remaining questions: How do ravens share this information? Vocalizations? How do they decide which individuals have reliable information? Calls of young birds Chicks pip a small hole through the inside membrane of the egg to provide an air bubble, start breathing and make vocal sounds. Chicks may synchronize their time of hatching based on the sounds made by their brothers and sisters. Parent birds anticipate hatching by listening to the peeping sounds made by chicks 1-2 days before hatching. Calls of young birds Cross-species variation in parental investment Precocial species need little parental care Altricial species need lots of parental care No parenting invertebrates Begging calls Parent birds of altricial species are stimulated to feed their offspring not only by brightly coloured gape patterns flashed at them by hungry young, but also by begging cries. of need for food Food provision is critical to a young bird s survival. The hungrier they are the greater the intensity of begging (honest signalling). of need for food But why don t they always beg at maximum intensity (dishonest signalling)? Nest parasites (e.g., European Cuckoo) Begging intensity Begging intensity maximum intensity Need for food Need for food 5

6 Cost-benefit analysis Begging is beneficial (stimulates food provision; well-fed chicks more likely to survive). Begging sounds induce parents to bring more food to the nest. Studies of Pied Flycatchers have shown that when one parent hears (tape-recorded) begging calls from the vicinity of the nest, they bring more food than the other parent (who doesn t hear them). Cost-benefit analysis Begging is costly (energy required to make sounds, increased risk of nest predation) Artificial nests are more likely to experience predation if tape recordings of begging sounds are played. Ground nesting birds are more susceptible to predation than tree nesters. Chicks raised in tree nests make louder begging sounds; those raised in ground nests use higher frequencies that do not travel as far. Cost-benefit analysis Trade-off between cost and benefit depends on the circumstances: a hungry chick benefits more from begging than a well-fed chick. The cost is the same, so the optimal course of action is to adopt the strategy of honest signalling (beg in proportion to hunger level). Predation may cost the chick its life, but also the lives of its siblings. Begging intensity is higher in brood parasites (European Cuckoo, Brown-headed Cowbird) that are unrelated to their host. Alarm calling in chickadees "Chick-a-Dee" Calls The number of syllables and acoustic structure of these syllables is highly variable among different "chick-a-dee" calls. Some of this variation apparently communicates information about individual and flock identity. This call is also used to communicate about predators, some of the acoustic variation also serves to code information about the type or level of threat of the predator being mobbed. Chickadee alarm calls encode information about predator size and risk. Alarm calling in chickadees Templeton C N, and Greene E PNAS 2007;104: by National Academy of Sciences 6

7 Alarm calling in chickadees Alarm calls in Tufted Titmouse Chickadees often form mixed flocks with other species of small song birds (especially in winter). Recent research suggests that other species of birds in the flock eavesdrop on chickadee mobbing / alarm calls and respond to the perceived threat level. Mean duration (±standard error) of mobbing responses (in seconds) of tufted titmice responding to raptors and controls during 6-min presentation periods. When presented with raptors of varying size, the number of total D-notes uttered per titmouse in the first 2 min of the trial period decreased with increasing body length of raptors. Courter J R, and Ritchison G Behavioral Ecology 2010;21: The Author Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please journals.permissions@oxfordjournals.org Courter J R, and Ritchison G Behavioral Ecology 2010;21: The Author Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please journals.permissions@oxfordjournals.org Bar graph showing the mean time (±standard error) before tufted titmice returned to normal feeding behavior after playback of chick-a-dee calls previously given to a small raptor (eastern screech-owl), a large raptor (red-tailed hawk), and a control (American robin mobbing calls). Social Eavesdropping hypothesis Beecher et al. (2006) found that young song sparrows learned more songs from adult song tutors they overheard singing with another bird ( eavesdropping ) compared to adult song tutors with whom they interacted socially ( direct interaction ). Courter J R, and Ritchison G Behavioral Ecology 2010;21: The Author Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please journals.permissions@oxfordjournals.org 7

8 Juvenile male song sparrows approach playback speakers broadcasting two birds singing interactively more than they do for solo song or control playback trials (p < ). Elephants Kingdom: Phylum: Class: Order: Family: Animalia Chordata Mammalia Proboscidea Elephantidae Genus: Species: Elephas maximus Templeton C N et al. Proc. R. Soc. B 2010;277: Asian Elephant 2010 by The Royal Society An Asian Elephant Imitates Human Speech Angela S. Stoeger, Daniel Mietchen, Sukhun Oh, Shermin de Silva, Christian T. Herbst, Soowhan Kwon, W. Tecumseh Fitch, An Asian Elephant Imitates Human Speech, Current Biology, Available online 1 November 2012) 8