Summary
O'Connor (1978) generated behavioral predictions from Trivers's (1974) theory of parent-offspring conflict (POC) in relation to avian brood reduction, especially for species using escalated sibling aggression. In general, when daily mortality rates fall between certain values (the “mortality difference thresholds” for parents and surviving offspring: O'Connor 1978), POC is expected. At such times parents and the early-hatching “senior” offspring are expected to disagree on the necessity, or at least timing, of the “victim” chick's death. Because that death is promoted directly by the senior chicks and because parents have realistic means of nullifying those efforts, behavioral conflict is expected. I examined the activities of all family members in one siblicidal (great egrets, Casmerodius albus) and one nonsiblicidal brood-reducing species (great blue herons, Ardea herodias) of ardeidae in Texas nesting colonies. Daily mortality rates over two breeding seasons approximated the predicted POC zone for four-chick (“B/4”) heron broods and three-chick (B/3) egret broods. As predicted, egret sibling aggression was significantly lower in two-chick broods. Herons seldom fought, regardless of brood size. Special attention was paid to the egret B/3 data for behavioral manifestations of POC. Parents did not interfere overtly with sibling fights (99.2% of 2,829), but parents seemed to have a subtle mollifying effect on the aggression (fewer “sever” fights occurred when parents were present). Parents showed no favoritism in food distribution to dying victim chicks. The mixed results are consistent with two rather different POC interpretations: (1) that significant conflict exists and the offspring are “winning” or (2) that there is no significant evolutionary conflict. In the latter case, parents are regarded as creating asymmetries among offspring (e.g., via hatch asynchrony), then leaving competition among siblings to run its course without further intervention (“laissezfaire” policy). This view explicitly recognizes that siblicide and other investment-skewing selfish chick behaviors may serve parental interests well-i.e., that equal allocation of resources is not likely to be the parental optimum. Using the relative reproductive values of each nestling as an index of the parent's unequal parental investment optimum produces a closer fit to the observed food distribution skew, but does not resolve the question of whether conflict remains.
Similar content being viewed by others
References
Alexander R (1974) The evolution of social behavior. Ann Rev Ecol Syst 5:325–383
Altmann J, Altmann S, Hausfater G (1978) Primate infant's effects on mother's future reproduction. Science 201:1028–1030
Bengsston H, Rydén O (1983) Parental feeding rate in relation to begging behavior in asynchronously hatched broods of the great tit Parus major. Behav Ecol Sociobiol 12:243–251
Blaker D (1969) Behaviour of the cattle egret Ardeola ibis. Ostrich 40:75–129
Braun B, Hunt G (1983) Brood reduction in black-legged kittiwakes. Auk 100:469–476
Cash K, Evans R (1986) Brood reduction in the American white pelican (Pelecanus erythrorhynchos). Behav Ecol Sociobiol 18:413–418
Charnov E, Krebs J (1974) On clutch-size and fitness. Ibis 116:217–219
Clutton-Brock T, Guinness F, Albon S (1982) Red deer. Behavior and ecology of two sexes. University of Chicago Press, Chicago
Drummond H (1987a) Parent-offspring conflict and siblicidal brood reduction in boobies. Proc 1986 Int Ornithol Congress, Ottawa (in press)
Drummond H (1987b) Parent-offspring conflict and brood reduction in the Pelecaniformes. Colonial Waterbirds (in press)
Drummond H, Gonzalez E, Osorno J-L (1986) Parent-offspring cooperation in the blue-footed booby (Sula nebouxii): social roles in infanticidal brood reduction. Behav Ecol Sociobiol 19:365–372
Eickwort K (1973) Cannibalism and kin selection in Labidomera clivicollis (Coleoptera, Chrysomelidae) Am Nat 107:452–453
Fujioka M (1985a) Food delivery and sibling competition in experimentally even-aged broods of the cattle egret. Behav Ecol Sociobiol 17:67–74
Fujioka M (1985b) Feeding behaviour, sibling competition and siblicide in asynchronous hatching broods of the cattle egret Bubulcus ibis. Anim Behav 33:1228–1242
Gargett G (1978) Sibling aggression in the black eagle in the Matapos, Rhodesia. Ostrich 49:57–63
Graves J, Whiten A, Heinzi P (1984) Why does the herring gull lay three eggs? Anim Behav 32:798–805
Hahn D (1981) Asynchronous hatching in the laughing gull: cutting losses and reducing rivalry. Anim Behav 29:421–427
Hausfater G, Hrdy S (eds) (1984) Infanticide: comparative and evolutionary perspectives. Aldine NY
Henderson B (1975) Role of the chick's begging behavior in the regulation of parental feeding behavior of Larus glaucescens. Condor 77:488–492
Horsfall J (1984) Brood reduction and brood division in coots. Anim Behav 32:216–225
Kahl MP (1964) Food ecology of the wood stork (Mycteria americana) in Florida. Ecol Monogr 34:97–117
Kluyver H, Van Balen J, Cave A (1977) The occurrence of timesaving mechanisms in the breeding biology of the great tit Parus major. In: Stonehouse B, Perrins C (eds) Evolutionary ecology. MacMillan, London, pp 153–169
Lack D (1954) The natural regulation of animal numbers. Clarendon Press, Oxford UK
Metcalf R (1980) Sex ratios, parent offspring conflict, and local competition for mates in the social wasps Polistes metricus and polistes variatus. Am Nat 116:642–654
Milinski M (1978) Kin selection and reproductive value. Z Tierpsychol 47:328–329
Mock D (1984a) Siblicidal aggression and resource monopolization in birds. Science 225:731–733
Mock D (1984b) Infanticide, siblicide, and avian nestling mortality. In: Hausfater G, Blaffer Hrdy S (eds) Infanticide: comparative and evolutionary perspectives. Aldine, New York, pp 3–30
Mock D (1985) Siblicidal brood reduction: the prey-size hypothesis. Am Nat 125:327–343
Mock D, Parker G (1986) Advantages and disadvantages of egret and heron brood reduction. Evolution 40:459–470
Mock D, Ploger B (1987) Parental manipulation of optimal hatch asynchrony in cattle egrets: an experimental study. Anim Behav 35:150–160
Mock D, Lamey T, Ploger B (1987) Proximate and ultimate roles of food amount in regulating egret sibling aggression. Ecology (in press)
Morris D (1986) Proximate and ultimate controls of life-history variation: the evolution of litter size in white-footed mice (Peromyscus leucopus). Evolution 40:189–181
Nuechterlein G (1981) Asynchronous hatching and sibling competition in western grebes. Can J Zool 59:994–998
Nur N (1984) The consequences of brood size for breeding blue tits II. Nestling weight, offspring survival and optimal brood size. J Anim Ecol 53:497–517
O'Connor R (1978) Brood reduction in birds: selection for fratricide, infanticide and suicide? Anim Behav 26:79–96
O'Gara B (1969) Unique aspects of reproduction in the female pronghorn (Antilocapra americana). Am J Anat 125:217–232
Parker G (1985) Models of parent-offspring conflict V Effects of the behaviour of the two parents. Anim Behav 33:519–533
Parker G, Macnair M (1979) Models of parent-offspring conflict IV Suppression: evolutionary retaliation by the parent. Anim Behav 27:1210–1235
Parker G, Mock D (1987) Parent-offspring conflict over clutch size. Evol Ecol (in press)
Parsons J (1976) Factors determining the number and size of eggs laid by the herring gull. Condor 78:481–492
Ploger B, Mock D (1986) Role of sibling aggression in distribution of food to nestling cattle egrets (Bubulcus ibis). Auk 103:768–776
Pugesek B (1981) Increased reproductive effort with age in the California gull (Larus californicus). Science 212:822–823
Røskaft E (1985) The effect of enlarged brood size on the future reproductive potential of the rook. J Anim Ecol 54:255–260
Russell E (1982) Parental investment and desertion of young in marsupials. Am Nat 119:744–748
Rydén O, Bengsston H (1980) Differential begging and locomotory behaviour by early and late hatched nestlings affecting the distribution of food in asynchronously hatched broods of altricial birds. Z Tierpsychol 53:209–224
Salfert I, Moodie G (1985) Filial egg-cannibalism in the brook stickleback Culaea inconstans (Kirtland). Behaviour 93:82–100
Siegfried R (1972) Breeding success and reproductive output of the cattle egret. Ostrich 43:43–55
Slagsvold T, Sandvik J, Rofstad G, Lorentsen O, Husby M (1984) On the adaptive value of intraclutch egg-size variation in birds. Auk 101:685–697
Smith C, Fretwell S (1974) The optimal balance between size and number of offspring. Am Nat 108:499–506
Smith J, Roff D (1980) Temporal spacing of broods, brood size and parental care in song sparrows (Melospiza melodia). Can J Zool 58:1007–1015
Sokal R, Rohlf J (1981) Biometry. 2nd edn. Freeman, San Francisco, CA
Stamps J, Metcalf R (1980) Parent-offspring conflict. In: Barlow G, Silverberg J (eds) Sociobiology: Beyond nature-nurture? Westview Press, Boulder, CO, pp 598–618
Stamps J, Clark A, Arrowood P, Kus B (1985) Parent-offspring conflict in budgerigars Behaviour 94:1–40
Stearns S (1976) Life-history tactics: A review of the ideas. Qu Rev Biol 51:3–47
stinson C (1979) On the selective advantage of fratricide in raptors. Evolution 33:1219–1225
Tepedino V, Frohlich D (1984) Fratricide in Megachile rotundata, a non-social megachilid bee: impartial treatment of sibs and nonsibs. Behav Ecol Sociobiol 15:19–23
thornhill R (1980) Rape in Panorpa scorpionflies and a general rape hypothesis. Anim Behav 28:52–59
Trivers R (1974) Parent-offspring conflict. Am Zool 14:249–264
Trivers R, Hare H (1976) Haplodiploidy and the evolution of social insects. Science 191:249–263
vom Saal F (1981) Variation in phenotype due to random intrauterine positioning of male and female fetuses in rodents. J Reprod Fert 62:633–650
Werschkul D (1979) Nestling mortality and the adaptive significance of early locomotion in the little blue heron. Auk 96:116–130
Wittenberger J (1981) Animal social behavior. Duxbury Press, Boston, MA
Young EC (1963) The breeding behaviour of the South Polar Skua. Ibis 105:203–233
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Mock, D.W. Siblicide, parent-offspring conflict, and unequal parental investment by egrets and herons. Behav Ecol Sociobiol 20, 247–256 (1987). https://doi.org/10.1007/BF00292177
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00292177