available, in Chaffinches about 1 in 150 nests contains a SUPERNORMAL CLUTCH of 7—8 eggs. In many species such larger-than-average clutches are laid by female pairs, and this may also be true in Chaffinches (although their specific association with same-sex pairing has not yet been demonstrated).
Nonreproductive and Alternative Heterosexualities
A variety of nonprocreative heterosexual behaviors are found in Chaffinches and Scottish Crossbills. Chaffinch couples sometimes copulate during incubation (i.e., after fertilization has occurred), and only 40—50 percent of all matings during the fertilizable period involve full genital contact. Some pairs may attempt to mate more than 200 times for each clutch of eggs they produce, as often as 4 times an hour. Mounts are often not completed for a variety of reasons: the male may slip off the female’s back or mount in a reversed head-to-tail position, or (more commonly) either partner may flee from the other out of fear or because of provocation from its mate. In fact, heterosexual courtship and mating in this species often entails a considerable amount of aggressive behavior between the sexes. Many birds do not participate in breeding at all: there are surplus flocks of single birds in many populations (males in Scottish Crossbills, both sexes in Chaffinches), as well as nonbreeding pairs in Scottish Crossbills. Interestingly, outside of the breeding season sexual segregation is also the rule. Males and female tend to migrate separately (wintering flocks are often same-sex), and females generally travel farther than males, often resulting in local populations with more males than females. In fact, this phenomenon has lent the Chaffinch its scientific name: coelebs means “bachelor” in Latin.
Scottish Crossbills frequently engage in “symbolic” matings early in the breeding season, in which the male mounts the female but no genital contact occurs. Sometimes these mounts are promiscuous: several males other than the female’s mate may participate. Nonmonogamous matings are also fairly common in Chaffinches, often between neighboring birds. About 8 percent of all mating activity involves nonmates, and 17 percent of all offspring (in a quarter of all broods) result from such copulations. Occasionally, a pair will separate or “divorce” during the breeding season, after which the single female may copulate with several already paired males. Eventually, a polygamous trio may develop if one of these males forms a pair-bond with her in addition to his own mate. Some Scottish Crossbills are also polygamous, forming trios of one male with two females. In this species, parents (in monogamous pairs) regularly become single parents: they separate when their young are able to fly, dividing the young between them and raising them on their own. Because the mother and father often travel to widely separated feeding grounds, youngsters belonging to the same family may be raised in very different environments. Occasionally, unrelated birds—both males and females—help feed and “foster-parent” the young birds after their biological parents have separated.
Adkisson, C. S. (1996) “Red Crossbill (
Halliday, H. (1948) “Song of Female Chaffinch.”
Hanski, I. K. (1994) “Timing of Copulations and Mate Guarding in the Chaffinch
Kling, J. W., and J. Stevenson-Hinde (1977) “Development of Song and Reinforcing Effects of Song in Female Chaffinches.”
Knox, A. G. (1990) “The Sympatric Breeding of Common and Scottish Crossbills
*Marjakangas, A. (1981) “A Singing Chaffinch
*Marler, P. (1956)
———(1955) “Studies of Fighting in Chaffinches. 2. The Effect on Dominance Relations of Disguising Females as Males.”
*Nethersole-Thompson, D. (1975)
Sheldon, B. C. (1994) “Sperm Competition in the Chaffinch: The Role of the Female.”
Sheldon, B. C., and T. Burke (1994) “Copulation Behavior and Paternity in the Chaffinch.”
Svensson, B. V. (1978) “Clutch Dimensions and Aspects of the Breeding Strategy of the Chaffinch
Voous, K. H. (1978) “The Scottish Crossbill
RED-BACKED SHRIKE
IDENTIFICATION: A small (61/2 inch) bird with a thick, hooked bill, grayish brown plumage, and a darker facial mask (black in males). DISTRIBUTION: Throughout Eurasia and northeast Africa; winters to southern Africa. NABITAT: Savanna, woodland, scrub, farmland. STUDY AREA: New Forest, Hampshire, England.
BLUE TIT
IDENTIFICATION: A tiny (41/2 inch) chickadee-like bird with a bright blue crown, black-and-white face, bluish green plumage, and yellow underparts. DISTRIBUTION: Europe, Middle East, North Africa. HABITAT: Woodland, human habitation. STUDY AREA: Marley Wood, Oxfordshire, England; subspecies
EASTERN BLUEBIRD
IDENTIFICATION: A sparrow-sized bird with bright blue plumage, white underparts, and a chestnut throat and breast. DISTRIBUTION: North and Central America. HABITAT: Open woodland, orchards, farmland, pine savanna. STUDY AREA: In the town of Washington, Michigan.
Social Organization
Red-backed Shrikes generally establish monogamous pair-bonds during the mating season and occupy partially overlapping territories. Outside of the breeding season, the birds are more solitary, and males and females typically occupy segregated habitats (males in more open bush country, females in more dense woodland). Blue Tits and Eastern Bluebirds are also territorial and form pair-bonds, but may associate in flocks outside of the breeding season.
Description
