Captive-rearing piping plovers: Developing techniques to augment ...

ZOO 538 Zoo Biology 16:461–477 (1997)

RESEARCH ARTICLES

Captive-rearing Piping Plovers: Developing Techniques to Augment Wild Populations Abby N. Powell,* Francesca J. Cuthbert, Lauren C. Wemmer, Alice W. Doolittle, and Shane T. Feirer Department of Fisheries and Wildlife, University of Minnesota, St. Paul, Minnesota

Techniques for captive-rearing and releasing piping plovers (Charadrius melodus) were developed using a surrogate species, killdeer (Charadrius vociferus). We compared captive- and parent-reared killdeer, and parent-reared piping plovers and determined that growth and behavior were similar. After surrogate trials determined that captive-rearing was feasible, we used the same methods to raise piping plover chicks from salvaged eggs. For captive-reared chick of both species, survival to fledging was higher than and behaviors similar to parent-reared chicks in the wild. Rearing techniques were fine-tuned, and ten piping plover fledglings were released to the wild. Based on our results, we developed recommendations for captive-rearing piping plovers using salvaged eggs to enhance productivity of small populations. Zoo Biol 16:461–477, 1997. © 1997 Wiley-Liss, Inc. Key words: killdeer; piping plovers; Charadrius melodus; Charadrius vociferus; endangered species; reintroduction; surrogate species

INTRODUCTION

Piping plovers (Charadrius melodus) were listed as federally threatened (Great Plains and Atlantic Coast populations) and endangered (Great Lakes population) in 1986 [U.S. Fish and Wildlife Service, 1985]. In the years since listing, populations remained relatively stable through 1991 [Haig, 1992]. Results from the 1996 International Census indicate a significant increase in the Atlantic Coast population, a significant decrease in Great Plains plovers, and no change in the Great Lakes population [J. Pissner, pers. comm.]. Management techniques have included protection of nesting areas from human disturbance, predator management, and vegetation control [Powell, 1991; Haig, 1992]. A population model for the Great Plains determined that

*Correspondence to: Abby N. Powell, USGS-Biological Resources Division, Northern Prairie Wildlife Research Center, Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701. Received for publication March 6, 1997; revision accepted August 29, 1997.

© 1997 Wiley-Liss, Inc.

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this population is likely to be extirpated in 24 hr. In the absence of recent information about the presence of incubating plovers, abandonment of completed clutches was presumed to have occurred when: no bird was seen on or near the nest when observation of the nest was initiated, no bird appeared or began to incubate within 1 hr of the initiation of observation, and no adult appeared or defended the nest when we approached it. Partial burial of eggs by sand and the absence of plover tracks around the nest constituted additional evidence that abandonment had occurred. Asynchronous hatching of eggs within plover clutches sometimes results in continued incubation of unhatched eggs by one adult while the other adult attends and broods chicks away from the nest. Unhatched eggs were presumed to have been abandoned when both adults were observed attending hatched chicks away from the nest and neither defended the nest when we approached it. Salvaged eggs included those abandoned during the incubation stage and eggs left in the nest after the other eggs hatched. We report numbers of salvaged eggs only for years when some salvaged eggs were viable. We salvaged eggs from seven piping plover nests (total = 14 eggs) in 1992, four nests (total = 18 eggs; one nest was a 6-egg clutch) in 1993, eight nests in 1996 (total = 15 eggs), and five nests (total = 11 eggs) in 1997. Eggs were transferred to small boxes lined with cotton

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inside a small cooler containing a hot water bottle. The eggs were transported immediately to UMBS and placed in a Lyon-Marsh incubator maintained under the same conditions reported for killdeer. Chicks were removed from the incubator as they hatched and were placed in a sand-lined box maintained at 34°C with a heat lamp. Chicks were provided with water in a shallow dish, live food (pin head crickets, small mealworms, chopped earthworms, and mayflies when available), and cobble and driftwood for cover. Chicks of different ages were separated by a partition for the first few days to prevent aggressive behavior by older chicks. Dummy adults made from socks and feather dusters were provided to allow chicks to be ‘‘brooded.’’ We minimized visual contact with plover chicks by providing food from behind a blind and played tape-recorded piping plover alarm calls to chicks when we approached. After 7 days, chicks were transferred to the same 2 × 4-m outdoor pens used for killdeer rearing in 1989. Soon after transfer, the plover chicks reduced their feeding frequency and did not gain weight at the expected rate. We returned them to sand-lined boxes indoors and placed them outdoors for a few hours on days when weather conditions were favorable for exposure to direct sunlight. The outdoor pen enclosed 6.1 × 9.1 m of natural sand beach and extended approximately 1 m into Douglas Lake, UMBS, to allow bathing opportunities and the development of natural foraging behaviors. A heat lamp was provided in a corner of the pen. Commercial mealworms, crickets, and wild insects caught in sweep nets were released in the center of the pen before the chicks were placed into the enclosure. We monitored chick activities in the outdoor pen from a blind. After this change in housing, the plovers continued to gain weight. When chicks were capable of flight (~35 days) they were released. Areas used but not fully occupied by wild plovers that had minimal human disturbance and predator activity were considered appropriate release sites. In 1992, we released the captive fledglings on an isolated beach at Vermilion Station (Chippewa County, MI) where monitoring was feasible for only 2 days after release. In 1993 and 1996, fledglings were banded with individual combinations of standard USFSW aluminum bands and colored plastic bands and released at Wilderness State Park (Emmet County, MI) where we were able to observe them on a regular basis until they disappeared from the site. RESULTS Survival of Captive-reared Surrogates

Four of the 22 killdeer eggs collected were infertile. All the fertile eggs hatched, and 14 chicks survived to fledging (Table 1). Mortality occurred within the first 3 days of hatching when the chicks failed to thrive. Captive-reared killdeer chicks responded to taped alarm calls by crouching and freezing in place when less than 2 weeks old; they gave alarm calls and ran to cover after age 2 weeks. Captive-reared fledglings remained together at the release site for 3 days after release and then dispersed. One of the 14 captive killdeer fledglings that was released returned to the study area as a 1-year-old bird. The captive-reared killdeer was of unknown sex and was seen among a flock of wild killdeer on the mainland ~50 km from its release site. Survival of Parent-reared Killdeer and Plovers in the Wild

We located 22 killdeer nests and 11 piping plover nests. Hatching rates were higher for wild piping plovers than killdeer during the years that behavior was re-

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TABLE 1. Reproductive success of captive- and wild-reared killdeer and piping plovers

Killdeer Wild Captive Piping plovers Wild (this study) Wild (1988–97)a Captive a

No. nests

No. eggs

% Hatched

% Fledged

22 6

90 22

54 82

27 78

11 196 21

41 736–748 22b

85 79–86 59

37 50–55 77

Michigan piping plovers, unpublished, Michigan Department of Natural Resources. Potentially viable eggs (58 eggs salvaged).

b

corded (Table 1). Fledging rates were higher for wild piping plovers than killdeer both during the study years and over an 8-yr average (Table 1). No piping plovers eggs were destroyed by predators, but one incomplete clutch was destroyed by wave action during a storm. Killdeer eggs were eaten by coyotes (Canis latrans), American crows (Corvus brachyhynchos), and possibly ring-billed gulls (Larus delawarensis). In one case, a killdeer egg was broken by children but the three remaining eggs subsequently hatched. Known predation on piping plover chicks was due to avian predators. Chick mortality occurred before age 1 week for all piping plover chicks and 76% of killdeer chicks that died. Behavioral Comparison of Parent-reared Surrogates and Parent-reared Piping Plovers

From hatching to fledging, we observed eight wild killdeer and eight piping plover families, for a total of 1,560 observation-hours during 1987–1989. Families that lost all chicks within 1 day after hatching were discounted from the analysis. Adults of both species brooded their chicks on the nest on the day of hatching. Nonbrooding parents remained close to their nests (usually within 5–10 m) during this time. Both killdeer and piping plover families left nest sites within 24 hr of hatching. Diurnal brooding activity continued for the first 2 weeks after hatching and was associated with weather conditions and the age of chicks. In cases where the sex of parents was known, male piping plovers spent 23% less time brooding than females during the day (39% males; 62% females; n = 8 pairs). Adults and chicks of both species initiated brooding events. Chicks initiated brooding by approaching the attending adult. Parents responded to chick approaches with a soft brooding call and stood so chicks could move underneath them. Chicks foraging nearby often responded to the brooding call and joined the sibling being brooded. Adults initiated brooding by crouching, fluffing their feathers, and giving brooding calls. During daylight hours, killdeer brooded chicks younger than 10 days and piping plovers brooded chicks less than 14 days old. Killdeer did not maintain distinct brood-rearing territories, but defended areas around the chicks as they traveled over large areas. Killdeer used a broad range of habitats for brood rearing including beach shorelines, mowed yards, pastures, and plowed cornfields [Powell and Cuthbert, 1993]. Killdeer families exposed to human disturbance moved frequently, and over longer distances, than families rearing young in remote areas. In one case, a killdeer family with 5-day-old chicks moved over 1 km within 48 hr. In contrast, piping plovers led their chicks to beach shorelines for

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brood rearing, and defended brood-rearing territories along the lakeshore [Powell and Cuthbert, 1992]. Piping plover families remained within 100 m of a line perpendicular to their original nest site. However, two piping plover families exposed to human activity remained within 200 m of their nest site and returned to a general brood-rearing area after being displaced by disturbance. Parents of both species remained with their broods until fledging or loss of chicks in all cases. In two piping plover families, the female parent disappeared 30 days after hatching and the males remained with their broods for several weeks after fledging. Adults that lost their chicks left the study areas within 5 days; renesting only occurred after egg loss. In contrast, killdeer occasionally renested after raising a brood. Killdeer and piping plover adults exchanged duties as brood attendants. Attending parents stood or sat in a location where their young were visible and oriented toward the chicks (piping plovers 88%; killdeer 84% of time observed). Attending parents of both species maintained close contact to their broods by gathering them using vocalizations and physical means. Parents were seen chasing and leading young in response to disturbance by humans and predators. Although attending parents occasionally fed alongside chicks, these foraging bouts lasted