Inferring Breeding Success Through Radiotelemetry in the Marbled Murrelet

Abstract

Demographic parameter estimates are essential for understanding population ecology and developing management plans for species of concern. We inferred measures of breeding success using radiotelemetry in the marbled murrelet (Brachyramphus marmoratus), a secretive, forest‐nesting seabird, from 1998 to 2001 in Desolation Sound, British Columbia, Canada. Our estimates of mean annual nesting success and fecundity (0.19–0.23 female offspring/adult female/yr) are among the highest reported for the species. We suspect that our estimates are high compared to previous estimates in our study area (Manley 1999), primarily because of our higher success in areas inaccessible to ground‐based human observers. We detail how behavior‐based inferences of activity at different reproductive stages did not differ between confirmed nest sites and suspected nest sites that were physically inaccessible to us. We were able to accurately predict initiations of breeding and incubation success from the duration of adults' repeated daily shifts from the ocean to their inland nest sites. Chick‐rearing success was accurately predicted by visitation rates of adults during provisioning. We discuss the assumptions and potential biases of our methods and their effects on our results. Our method may overestimate early breeding failure, but it likely provided unbiased fecundity estimates for our population. Accurately inferring breeding success through radiotelemetry is costly and labor intensive. However, radiotelemetry could provide crucial demographic information once thought impossible to obtain for secretive breeding species.

Breeding Ecology of Kittlitz's Murrelets at Agattu Island, Aleutian Islands, Alaska

“…Our Mayfield estimate of nest survival for Kittlitz's Murrelets was 6%, which was lower than the apparent nest survival of Marbled Murrelets (28%, N = 32 nests, Nelson and Hamer 1995; 48%, N = 116 nests, Bradley et al 2004). Low reproductive success at Agattu Island was due to a combination of egg predation and exposure of chicks to inclement weather.…”

“…The tribe Brachyramphini is a monophyletic lineage of alcids that contains three species: Kittlitz's Murrelets (Brachyramphus brevirostris), Marbled Murrelets (B. marmoratus) and Longbilled Murrelets (B. perdix; Friesen et al 1996a). Brachyramphus murrelets are unusual among seabirds because these small-bodied species nest solitarily, on the ground at inland sites and on large tree branches in old growth forests (Murphy et al 1984;Nelson 1997;Day et al 1999;Bradley et al 2004). Nests of murrelets are extremely difficult to locate because these birds use inaccessible sites in remote habitats, because nests are highly dispersed at distances up to 70 km from the ocean, clutch size is only one egg and because the cryptic young are left alone at the nest shortly after hatching.…”

Full Issue

“…Detecting actual fledging dates on the basis of behavior patterns from radio telemetry was difficult because estimated dates of egg laying and hatching might be off by as much as a few days, and chick-provisioning rates can differ considerably during late stages of the nestling period (Nelson andHamer 1995b, Bradley et al 2002). Consequently, we adopted the approach of Bradley et al (2004) to infer the duration of nesting attempts and defined ''successful fledging'' as adult behavior patterns consistent with chick provisioning for !20 days. This method of estimating fledging success is biased high because it does not include nests that failed late in the nestling period, but this method was the only viable option for monitoring widely dispersed nests located in inaccessible habitat.…”

Limited foraging flexibility: increased foraging effort by a marine predator does not buffer against scarce prey

“…Adult survival has been linked to large-scale oceanographic conditions; survival increased in warmwater years (Peery et al 2006). In British Columbia, Canada, annual adult survival rates are quite high (range 0.829 to 0.929, Cam et al 2003); thus, low reproductive rates (0.16 to 0.23 female offspring female adult -1 yr -1 , Burger 2002, Bradley et al 2004) are likely contributing to population declines.…”