Age-Related Differences In Foraging Ability Among Clam-Dropping Herring Gulls (Larus argentatus)
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Abstract:
Juvenile birds are generally less efficient foragers than adults, and this can lead to reduced survival or delayed reproduction. Feeding on hard-shelled nuts and mollusks after breaking them open by dropping is particularly challenging. To determine whether juvenile birds are as proficient as adults at this complex foraging task, we compared juvenile and adult Herring Gulls (Larus argentatus) feeding at low tide by dropping clams (Rangia cuneata) at a coastal estuary in Virginia, USA. Juvenile (first-winter) gulls were less successful than adult (2 years old) birds at finding clams to drop. Moreover, the clams they selected were of a wider range of sizes, more often being difficult to handle or of lower nutritional value. Juveniles did, however, drop clams with the same degree of success as adult birds. Together these results suggest that learning to find and recognize profitable clams is the developmental bottleneck in this complex behavior.Keywords:
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Juvenile birds are generally less efficient foragers than adults, and this can lead to reduced survival or delayed reproduction. Feeding on hard-shelled nuts and mollusks after breaking them open by dropping is particularly challenging. To determine whether juvenile birds are as proficient as adults at this complex foraging task, we compared juvenile and adult Herring Gulls (Larus argentatus) feeding at low tide by dropping clams (Rangia cuneata) at a coastal estuary in Virginia, USA. Juvenile (first-winter) gulls were less successful than adult (2 years old) birds at finding clams to drop. Moreover, the clams they selected were of a wider range of sizes, more often being difficult to handle or of lower nutritional value. Juveniles did, however, drop clams with the same degree of success as adult birds. Together these results suggest that learning to find and recognize profitable clams is the developmental bottleneck in this complex behavior.
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The history of herring gull (Larus argentatus) populations nesting along the North Shore of the Gulf of St Lawrence and the commercial fishing activities there are closely related. Coastal cod (Gadus morhua) supply the main fishery in this part of the Gulf and traditionally have resulted in significant amounts of fish offal being discarded at sea and in fishing ports. Using commercial catch data of cod landings, and information from herring gull surveys conducted in the migratory bird sanctuaries on the North Shore from 1925 to 1993, the relationship between the cod fishery and herring gull populations was investigated. Between 1925 and 1975 the fisheries harvested a mean of 5 234 t of cod annually, with high and low catches of 11 000 and 1 700 t, respectively. During the same period, the herring gull population in the sanctuaries increased from 650 to 8 000 pairs. After 1975, and until 1993, the annual mean harvest was 5771 t peaking in 1983 at 11 500 t. There was then a steady decline until a complete fishery collapse in 1993. During the same period, the herring gull population increased from 8 000 pairs in 1975 to 14 000 pairs in 1988, but then dropped dramatically in most sanctuaries and was estimated at only 3000 pairs in 1993. This general decline of gulls appears to be related to the decrease in commercial fishing activities in the region, but not uniformly so.
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Commercial fishing
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Common Eider (Somateria mollissima dresseri) breeding success and gull-eider interactions were studied at Stratton Island, Maine in 2004 and 2005. Eiders suffered little nest predation, and most egg losses to gulls were either facilitated by researcher intrusions or confined to newly initiated, unattended nests. Despite high nest success (>80%) in both study years, predation watches indicated that few, if any, ducklings survived to fledging as a result of extreme harassment and predation by Great Black-backed Gulls (Larus marinus). Gull attacks were opportunistic, involved one to 36 gulls, and often resulted in complete crèche destruction. Herring Gulls (L. argentatus) also took occasional young and eggs. Although Stratton Island is managed as a tern restoration site, and gull control measures to enhance tern productivity include nest destruction and shooting of tern predators, gulls continued to congregate around crèching areas and to prey on ducklings. We suggest that additional gull control measures, particularly at a nearby gull colony, may enhance duckling survival. We also recommend monitoring of other eider colonies in the region to better assess duckling survival and recruitment rates.
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Animal ecology
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Dietary specialization, exploiting a small fraction of available food resources, is commonly reported for gulls and skuas. Predation of birds by these species is usually considered a specialist strategy employed by the minority of the population but non-specialists also predate birds and may actually have a greater impact on the prey species. To date, most studies have focused on predatory bird-specialists, down-playing the possible importance of opportunistic predation by non-specialists. We addressed this by studying diet (regurgitated pellets and prey remains) and behavior of breeding Herring Gulls (Larus argentatus) over three summers at Gull Island, a mixed-species breeding colony in Lake Ontario. One-third of all pellets analyzed contained bird remains, primarily the most numerous breeding bird: Ring-billed Gull (L. delawarensis) chicks (51%) and adults (36%). Although all but one pair of Herring Gulls ate birds, all pairs maintained broad and mostly similar diets, with birds accounting for at most one-third of prey. Behavior also indicated that Herring Gulls at Gull Island were not predatory bird-specialists because predation was too infrequent to meet energetic requirements, was largely unsuccessful and was only ever observed when Ring-billed Gulls strayed into Herring Gull breeding territories. Instead, bird predation appeared mainly opportunistic, increasing with seasonal availability, access to shoreline, proximity to nesting Ring-billed Gulls and breeding territory size. Compared with predatory specialist Herring Gulls in the same region, individuals that predated birds at Gull Island did not display specialist behaviors and killed six times fewer birds (0.1–0.4 per day, on average) but were over 20 times more numerous (98% of the population versus 4%). Thus, our results indicate that opportunistic predation by non-specialists may have important consequences for prey species. Since opportunistic predation cannot be effectively managed using techniques widely advocated for specialist predators, it is essential to investigate cause of predation by large gulls prior to lethal management.
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Abstract White phosphorus (P4) has been identified as the cause of mortality for dabbling ducks and swans at an estuanne salt marsh in Alaska Predation of ducks poisoned by P4 was monitored to assess the extent and range of predator exposures to P4 Avian tissues were analyzed for P4 by gas chromatography We observed that both sick and dead dabbling ducks were common prey of bald eagles (Hahaeetus leucocephalus), herring gulls (Larus argentatus), and common ravens (Corvus corax) Frank signs of P4 intoxication attracted predators and rendered the ducks easy prey White phosphorus was found in the tis sue remains of ducks that had been preyed upon, thus providing positive evidence that predators were exposed to P4 Although P4 varied widely among individuals, P4 was generally highest in the gizzard contents followed by fatty tissues such as fat depots and the skin White phosphorus was identified in fatty tissues of one eagle and in one herring gull egg, thus providing direct evidence of absorption of P4 by predators
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Herring gull
Antigenicity
Charadriiformes
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Kleptoparasitism is a foraging strategy whereby an individual steals a procured food item from another individual. Individuals can optimize their kleptoparasitic foraging strategy by modifying their behaviour to expend less energy than they would by foraging independently or by attacking more profitable hosts. Individuals vulnerable to becoming a host to a kleptoparasite can modify their behaviour to reduce the risk of losing prey to a kleptoparasite by using tactics such as handling food in areas inaccessible to the kleptoparasite or landing in groups. Observations of individual herring gulls (Larus argentatus) and approaches to the burrow slope by Atlantic puffins (Fratercula arctica) were conduced in summer 2018 on Gull Island, Newfoundland and Labrador. The findings of this study suggest that herring gulls optimize their kleptoparasitic foraging strategy by targeting more profitable hosts, and that puffins at risk of kleptoparasitism effectively mitigate their risk by engaging in evasive behaviour.
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We studied egg loss in Herring Gulls Larus argentatus on the Dutch Frisian Island of Terschelling. Conspecific egg predation was the main cause of egg loss. Late breeding, a small inter-nest distance and a low vegetation cover enhanced egg predation. Predation was more frequent in nests with small eggs than in nests with large eggs. The effect of egg volume on predation was experimentally investigated by exchanging clutches between pairs. Increasing differences in egg size between original and adopted clutches increased progressively the predation rate. Egg predation was strongly correlated to the original clutch volume (control and experimental pairs combined). No correlation was observed between egg predation and the volume of the adopted clutches. This excludes a possible predator-linked selection mechanism. It is suggested that lower quality birds not only lay smaller eggs but also exhibit less efficient parental care during the incubation period, resulting in an increased predation risk. DLO Institute for Forestry and Nature Research (IBN-DLO), Department of Animal Ecology, P.O. Box 23, NL-6700 AA Wageningen, The Netherlands.
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Avian clutch size
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