Bill Length of Herons and Egrets as an Estimator of Prey Size

Bayer, Range D.

doi:10.2307/1521059

Cited by 34 publications

(7 citation statements)

References 15 publications

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“…In this way fish were divided into prey sizeclasses (Table 1). We did not practice estimating fish lengths with captive or model birds in the field as suggested by Bayer (1985) forArdeidae. However, there are bill size differences (approximately 0*5 cm) between males and females (Piersma 1985) and there could be problems with estimating the size of large prey (2-4 times bill length) (Bayer 1985).…”

Section: Fish Size and Weightmentioning

confidence: 99%

“…We did not practice estimating fish lengths with captive or model birds in the field as suggested by Bayer (1985) forArdeidae. However, there are bill size differences (approximately 0*5 cm) between males and females (Piersma 1985) and there could be problems with estimating the size of large prey (2-4 times bill length) (Bayer 1985). If a grebe caught a fish larger or smaller than the size-class initially stocked, fish wet weight was estimated from fish length, using standard relationships between fish weight and length based on an OVB report (Baarda & Kampen 1988).…”

Section: Fish Size and Weightmentioning

confidence: 99%

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Foraging of the Great Crested Grebe in Relation to Food Supply

Ulenaers¹,

Vessem²,

Dhondt³

1992

The Journal of Animal Ecology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. Foraging data for great crested grebes (Podiceps cristatus L.) feeding in shallow fish-ponds (0 8-1 m deep) were used to test whether pond characteristics, fish density, mean wet weight of the fish or fish species influenced foraging behaviour and success in this fish-eating grebe. 2. When fishing for roach/rudd (Rutilus rutilus L.IScardinius erythropthalmus L.), the number of prey eaten per unit time foraging was positively influenced by the proportion of successful dives, and negatively by the mean diving time. The proportion of successful dives increased as fish weight decreased. Mean diving time, however, was not related to any component of the food supply, nor to pond characteristics. 3. The overall mean diving time was low in comparison with other studies, probably because the study ponds were so shallow. Since the water depth was equal in each pond, mean diving time is not an accurate measure of fish densities in shallow waters. 4. When roach/rudd were the prey, handling time above the water did not constrain the number of prey eaten per unit time foraging at any fish density. With roach/rudd and carp (Cyprinus carpio L.) as prey, the above-water handling time increased with the size of the fish consumed. The total handling time under and above the water surface together constituted on average 4-7% of the time required to consume one fish. 5. When fishing for roach/rudd, successful dives lasted significantly longer than unsuccessful ones. As the mean duration of successful dives increased with fish weight, we suggest that this can be explained by handling prey under water. For carp, however, this could not be shown. Furthermore, unsuccessful dives lasted significantly longer when fishing for carp than for roach/rudd. This is probably related to behavioural differences between the fish species. In roach/rudd ponds, it seemed that grebes took on average the smaller fish.

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Section: Fish Size and Weightmentioning

confidence: 99%

Section: Fish Size and Weightmentioning

confidence: 99%

Foraging of the Great Crested Grebe in Relation to Food Supply

Ulenaers¹,

Vessem²,

Dhondt³

1992

The Journal of Animal Ecology

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“…To estimate size, we used heron culmen length as a reference (14 cm; e.g., Bayer 1985;Parkhurst et al 1992;Pitt et al 1998) and recorded prey lengths to the nearest one-quarter bill length (3.5 cm). Some prey items were too small to identify and were recorded as having lengths of less than 3.5 cm.…”

Section: Methodsmentioning

confidence: 99%

Great Blue Heron Predation on Stocked Rainbow Trout in an Arkansas Tailwater Fishery

Hodgens¹,

Blumenshine²,

Bednarz³

2004

North American Journal of Fisheries Management

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Fisheries managers seldom have adequate information to assess their stock losses to avian piscivores, which function as apex predators in many aquatic food webs. Our primary objective was to estimate the number of stocked rainbow trout Oncorhynchus mykiss consumed by great blue herons Ardea herodias on the Bull Shoals and Norfork tailwaters of north‐central Arkansas. Between November 2000 and December 2001, we periodically surveyed great blue herons along 150.7 river km on the tailwaters of the Bull Shoals and Norfork dams. Heron density (number/km) in or along the river ranged from 0 to 4/km per survey, with the highest mean number located near the Bull Shoals Dam (2.31 herons/km). We recorded 467 prey captures by herons during 202 observation hours. Sculpin Cottus spp. were the most common prey (N = 120). Most prey (87%) measured 14 cm or less in length, and most captured live trout (85.4%) fell between 10.5 and 28.0 cm in length. While live trout represented only 48 of 359 identifiable prey items (13%), they comprised an estimated 62.8% of heron diet biomass. We developed a bioenergetics model that combined our observations with published metabolic coefficients and relationships to estimate heron energy demand during breeding and nonbreeding seasons. This analysis revealed that trout comprised an estimated 67% of heron daily energy demand in the study area. Heron daily energy demand peaked during the breeding season (March–May). Based on a mean monthly population estimate of 227 great blue herons requiring 156 million kJ of total energy/year, we calculated that herons consumed just under 50,000 catchable‐sized stocked trout annually. This loss to great blue herons represents an estimated 2.4% of the approximately 2 million trout stocked in the study area. Thus, great blue heron predation likely represents only a minor source of trout mortality in the Bull Shoals and Norfork tailwaters.

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“…fish, frog or tadpole). Prey size was estimated by comparing prey length to the length of a Snowy Egret bill (7.9 cm) (Bayer 1985;Brzorad et al 2004). A length weight regression (R 2 > 0.90) previously established by measuring a random sample of 113 fish collected at this site (Maccarone and Brzorad 2007) was used to convert body lengths into weights.…”

Section: Foraging Activitiesmentioning

confidence: 99%