Male Shrikes Research Articles

Effects of habitat use on food acquisition and food caching during a nonbreeding season in a winter-breeding, food-storing passerine

ABSTRACT Capsule: Wintering male Bull-headed Shrikes Lanius buchepalus preferred vegetable fields with perch sites to search for and detect terrestrial prey, and males occupying territories with large areas of vegetable fields acquired more prey and cached more food. Aims: To better understand effects of habitat use on food acquisition and food caching of the Bull-headed Shrike, we investigated relationships between habitat quality (measured through foraging-site selection and foraging success) and food caching during the non-breeding season. Methods: We monitored 66 territorial male shrikes during the non-breeding season from 2014 to 2016, and collected data on foraging-site selection, foraging success, and food caching. Results: Our field observations showed that male shrikes preferred to forage over vegetable fields and that males occupying territories incorporating large areas of that habitat were able to acquire more food items and store more food caches in their territories during the nonbreeding season. Conclusion: We suggest that for male Bull-headed Shrikes, a winter-breeding food-storing passerine, the quality of habitat in the nonbreeding season has the potential to affect their subsequent fitness.

Unmasking Zorro: functional importance of the facial mask in the Masked Shrike (Lanius nubicus)

The facial mask is a prominent feature in the animal kingdom. We hypothesized that the facial mask of shrikes allows them to hunt into the sun, which accords them detection and surprise-attack capabilities. We conducted a field experiment to determine whether the mask facilitated foraging while facing into the sun. Male shrikes with white-painted masks hunted facing away from the sun more than birds with black-painted masks, which are the natural color, and more than individuals in the control group who were not painted. Furthermore, individuals with white-painted masks hunted at a greater angle in relation to the sun during the experiment than after the paint had eroded from the masks. Mean hunting success was significantly reduced in birds with white-painted masks compared with individuals with black-painted and natural masks. Moreover, individuals with white masks hunted with lower success during the experiment than in the following week when they reverted to their natural mask. We conclude that the facial mask of the Masked Shrike helps overcome the glare of the sun, perhaps allows better identification of prey from their larger shadow, and allows the shrike to approach the prey without alerting it to the stealth attack.

Hand-Reared Loggerhead Shrikes Breed in Captivity

Many continental populations of the Loggerhead Shrike (Lanius ludovicianus) have been declining in abundance for a number of years (Robbins et al. 1986, Brooks and Temple 1990, Lowe and Butcher 1990), and the San Clemente Island subspecies (L. 1. mearnsi) in California is highly endangered (Scott and Morrison 1990). Consequently, biologists have become increasingly interested in using manipulative techniques to study factors underlying the decline and to augment or restore wild populations. These techniques include the release of captive-raised and captive-bred shrikes, the translocation of adults, their eggs and young, and related manipulations (Kuehler et al., in press). It seems worthwhile, therefore, to report some details on the successful breeding of this species in captivity in 1971, especially as the loggerhead has not previously bred in captivity, and the few successful attempts with Eurasian species (L. collurio, L. excubitor, L. schach, and L. vittatus) have, with one exception (Giinther 1904), involved wild-caught, adult pairs (England 1970, 197 la, 1971b; Weischner 1989). The breeding pair of loggerheads came from a group of eight young shrikes taken from nests in northeastern Colorado in June, 1970, and hand-reared from the age of 8-9 days. These shrikes were transported to Dryden, New York as nestlings and were kept together until late September, when increasing aggression necessitated separation. During this period the birds were trained (Cade 1962, 1967) and allowed daily flights outside their cage as part of a study of the development of their hunting and impaling behavior. During fall and winter, individuals were housed indoors in separate, wire-mesh cages measuring 1.2 m in each dimension. The cages were arranged so that all the birds could see and hear each other. Five birds contracted avian pox and died during the winter; the three survivors were two males and a female. In mid-April, 1971 one of the male shrikes began a daily routine of singing and displaying in an extreme upright posture, leaning somewhat backward with its beak pointed straight up, and often turning slowly to one side or the other in this extreme upright posture while quivering its wings and singing. The behavior appeared identical to that of captive Northern Shrikes (Lanius excubitor) observed previously (Cade 1962). On 19 April, this bird was transferred to the Behavioral Ecology Building (Hawk Barn) at the Cornell University Laboratory of Omrnithology and placed in a chamber measuring 3 m wide by 6 m long and varying from 4.2-6 m high. The room had been provided with several freshly cut, leafless willow (Salix sp.) shrubs and hawthorns (Crataegus sp.) ranging from 2-3 m high to simulate a natural environment. Some branchlets were broken and sharpened to provide convenient impaling devices. Throughout the breeding season, laboratory mice, nestling sparrows and starlings, and dayold cockerels were provided for food. In addition, some insects (beetles, wasps, flies) entered the room from an open, wired front and were eaten. Later, an old but well-formed nest of the Brown Thrasher (Toxostoma rufum) was affixed 1.5 m up against the trunk of a hawthorn, and twigs, dry grass, cotton tufts, and wool yarn were placed on the floor for nesting materials. In a few days, the male appeared at ease in his new chamber, singing and displaying from several prominent perches. On 27 April, the female shrike was let loose in the chamber. She perched low in the middle of a hawthorn and did not move. The male flew down and hopped all around in branches near her. She did not flee, vocalize, or attempt to fight but sat still in a I Received 13 April 1992. Accepted 27 July 1992. SHORT COMMUNICATIONS 1027