The following article is reprinted from Vol. 18, No.2 (Summer 1995) of the IWRC Journal of Wildlife Rehabilitation with the permission of the author and the International Wildlife Rehabilitation Council (IWRC). The IWRC is a membership organization dedicated to furthering and disseminating knowledge in the field of wildlife rehabilitation. Membership and literature may be obtained by contacting the IWRC, 4437 Central Place, Suite B-4, Suisun, CA, 94585, or by calling (707) 864-1761.

Abstract

Black-chinned Hummingbird mothers and their nestlings are very quiet during feeding. After leaving the nest, however, the hungry young make a loud call to attract their mother's attention. The following is a discussion of silence as a possible security strategy to protect nestlings. Rehabilitators may use calling from the nest as an indication of abandoned young.

Key Words: Black-chinned Hummingbird, Archilocus alexandri, nestling behavior

Introduction

Skutch (1976) noted that feeding rates of parents in many altricial birds seems to be regulated by the level of noise generated by hungry nestlings. Nestling begging behavior is not always essential to stimulate the bringing of food, however. Skutch (1976) also recorded parents offering food to eggs, and even to long dead nestlings. He suggested that during the incubation and nestling period parental focus is on the nest and its contents, rather than the individual offspring. Examples of this focus are parents that ignore offspring separated from the nest or clutch. Many birds also fail to respond to an increased number of nest inhabitants (e.g., as by cowbird and cuckoo). After fledging, parental focus seems to switch from nest to individual offspring.

Behavioral Observations

Loud vocalizations by nestlings have been associated by Skutch (1976) and others, with birds such as woodpeckers, tanagers, and flycatchers. Many rehabilitators report observing stimulus evoked nestling vocalizations in kestrels, doves, cuckoos, swifts, woodpeckers, flycatchers, swallows, nuthatches, wrens, finches, old world sparrows, starlings, and others, both in the wild and in rehabilitation circumstances (England, Hamburg, Harden, Kyle, pers. comm.).

The author's observations of the behavior of Black-chinned hummingbirds (Archilocus alexandri) during the period of raising young, suggest that these nestlings remain absolutely silent. Neither nestlings nor the mother seem to vocalize prior to or during feeding episodes. This silence is also observed when orphaned Blackchinned nestlings are being raised in captivity (pers. obs. N=>50).

Fledging in juvenile Black-chinned hummingbirds is usually sudden and complete. After several days of wing exercise, while holding on to the nest tightly with the feet, the young bird lets go, and flies to a perch a meter or more from the nest. At this stage the fledgling begins to practice flight and feeding behaviors. It extends its tongue to everything within reach. As flight capabilities improve, and tongue placement produces some nutrient reward, the bird begins to learn how to forage. While still dependent on maternal care, the young bird signals its location to its mother by the use of a high, thin peep, sometimes called a squeak (Bent 1940, Schuchmann, 1988). This location call is easily heard, but as Cogswell (1949) observed, locating the source of the sound is usually circumstantial, as the call is highly nondirectional.

Fledglings in captivity use this call when they are hungry or distressed. During the two weeks after fledging the call is used less and less frequently as the bird develops its foraging capabilities.

Black-chinned hummingbirds often build nests in vulnerable places easily seen and reached by predators. They are particularly easy prey for avian predators. Johnsgard (1983) suggested that the low rates for fledging young reported by Stiles (1972) and others may be largely due to predation. He pointed out that Carpenter (1976) attributed the high nest success rate of 88.9% to the Andean Hillstar, speculating that they may avoid high predation losses due to their inhospitable and secluded nesting environment. Baltosser (1986) observed jays, orioles, and tanagers involved in predation and mobbing of nest sites. The author has seen roadrunners take birds about to fledge and has watched a female Black-chin, busily refurbishing a nest which had been successfully used for three years, abandon it after a starling's close examination. Here it is suggested that the unusual silence of nestling hummingbirds decreases the likelihood that the young will be taken by predators.

If the silence of the parent and nestlings is a behavioral strategy to increase security, calling from the nest, or strategic override, can be viewed by rehabilitators as a signal of extreme distress.

Wildlife Rescue of New Mexico receives many calls each year from people who have been watching "their" hummingbird nest, and have suddenly noticed that the mother isn't returning at night. Whether or not to recommend intervention is the question. Unless one can maintain a full hour of uninterrupted observation of the nest, one is likely to miss a 15-45 second visit from the adult. Vocalization by the nestlings is a good indication of abandonment. We recommend that the nest be left alone if the youngsters are silent. However, if the young birds call, the nest can be immediately cut down for delivery to a rehabilitator. Rarely does the mother show up the next day. If the female parent does appear, the author's 15 years of experience indicates that the nest can be successfully replaced at the original location, as female Black-chinned hummingbirds are tenacious parents.

Security Strategy Data

Two levels of observation were made. The first was observation of nestlings in the wild. No calling was heard from any of them until the birds fledged and left the nest. In older nestlings (18-20 days) a little chipping chatter was sometimes heard as they exercised their wings. Though this sound may jeopardize the security of the nestling, it is not the same call as the fledgling hunger call described above and seems to be made only in the enthusiasm of preflight practice (N=27). The second was that of calling nestlings arriving at Wildlife Rescue in the original nest. These birds were clearly in various stages of starving, some having been documented abandoned for as much as 40 hours. When their needs were met they stopped calling and did not resume that behavior until fledging (N=10). A variation of the above are the nests that we received before the birds showed evidence of acute distress. These were brought in when they were pruned out of a tree or when mother wasn't coming back to feed. These birds never called while in the nest. On leaving the nest they immediately vocalized, as though a switch had been thrown (N=6).

Acknowledgments

I thank the many individuals who made these observations possible by bringing abandoned hummingbird nestlings to Wildlife Rescue of New Mexico for care. Many thanks also go to David J. Ligon and William H. Baltosser for reviewing earlier drafts of this manuscript. Appreciation is expressed to the 'Share With Wildlife' Program of the New Mexico Dept. of Game and Fish (NMG&F) for financial assistance to Wildlife Rescue, and to NMG&F and The US Fish and Wildlife Service for permitting the activity.

Literature Cited

BALTOSSER, William H. 1986. "Nestling Success and Productivity of Hummingbirds in Southwestern New Mexico and South Eastern Arizona." The Wilson Bulletin 98(3):353-367.

BENT, Arthur Cleveland 1940. Life History of North American Cuckoos, Goatsuckers, Hummingbirds, and Their Allies, Part 11. New York, NY: Dover Publications Inc.

CARPENTER, P.L. 1976. "Ecology and Evolution of an Andean Hummingbird (Oreotrochilus estella)", Univ. Calif. Pub. Zool. 106: 174.

COGSWELL, Howard L. 1949. "Alternate Care of Two Nests in the Black-chinned Hummingbird." Condor 51:176-78

JOHNSGARD, Paul A. 1983. The Hummingbirds of North America. Washington, D.C.: Smithsonian Institution Press.

SCHUCHMANN, Karl. 1988. "Birds of the Air." Pacific Discovery. Summer, pp. 32-39.

SKUTCH, Alexander F. 1976 a. Feeding the Young in Parent Birds and Their Young. Univ.of Texas Press, Austin, TX pp. 261-280.

SKUTCH, Alexander F. 1976b. Education of Young Birds in Parent Birds and Their Young. Austin, TX Univ. of Texas Press. pp. 311-327.

STILES, F.G. 1972. "Food Supply and the Annual Cycle of the Anna Hummingbird." Univ. Calif. Pub. Zool. 97:1-109.