Heron Diet Research Articles

Foraging Habitat Availability and the Non-Fish Diet Composition of the Grey Heron (Ardea cinerea) at Two Spatial Scales.

Habitat structure on foraging ground is one of the crucial factors determining diet diversity in colonially breeding avian predators. Quantifying the habitat and diet composition at different spatial scales (regional and local inter-colonial) can help provide understanding of the drivers of diet composition. In this study, we examined the composition of the non-fish diet of an opportunistic predator, the Grey Heron (Ardea cinerea), based on pellets. We compared pellets from 21 colonies in two different regions of Poland that differing in composition of foraging habitats. Multivariate statistical techniques were used to analyze the relationship between diet and habitat compositions in a 20 km radius around these colonies. Significant inter-regional and inter-colony differences in Grey Heron diet and habitat composition were detected in foraging areas. However, some prey were present in the diet only from one of the regions. Around the heronries with a predominance of farmland habitats, the European water vole (Arvicola amphibius) and terrestrial invertebrates were present in relatively low frequencies, and the striped field mouse (Apodemus agrarius) was present in high frequencies. Voles (Microtus sp.) were more frequent in colonies with prevalence of non-irrigated arable land around the colony, in contrast to the bank vole (Myodes glareolus), which was less common in heronries with a higher contribution of this habitat type. Remains of aquatic invertebrates were less abundant in colonies surrounded by extensive forests. The results of our research indicate the opportunistic character of the non-fish part of the diet of the Grey Heron adapted to the local foraging habitat and prey availability.

Shifts in Great Blue Heron Habitat use Following Nest Site Usurpation: Implications for Salmonids

Abstract Interactions among predators can have important consequences for lower trophic levels. Here, we use individual tag data on juvenile salmonids to quantify how their geographic, taxonomic, and life-history representation in the diets of great blue herons (Ardea herodias) changed after a pair of bald eagles (Haliaeetus leucocephalus) usurped the colony's nesting site, forcing the colony to relocate. Heron diet composition changed significantly despite the short relocation distance (4.1 km). This was driven by a shift in space use, as herons to a greater extent began consuming fish from a river basin farther away from the bald eagle nest. As a consequence the species composition in heron diets changed significantly, with the largest increase in coho (Oncorhynchus kisutch) and largest decrease in Chinook salmon (O. tshawytscha). The representation of Chinook life-history types in the diets also shifted. Fall Chinook was the numerically dominant life-history type in the diets but decreased relative to ...

Trophic peculiarities of the Great Cormorant, Grey Heron and Long-tailed Duck on the Baltic Sea Lithuanian coast: a stable isotope approach

The stable isotopes of nitrogen (δ15N) and carbon (δ13C) were analysed in the feathers of the Great Cormorant (Phalacrocorax carbo), Grey Heron (Ardea cinerea) and Long-tailed Duck (Clangula hyemalis) staying in the different seasons at the Lithuanian Baltic Sea coast. Stable isotope ratios in bird feathers represented dietary variations and foraging habitats during the feather growth period. Adult Great Cormorants fed juveniles by smaller fish at the beginning of fledging, switching later to larger prey. The stable isotope analysis indicated that the Grey Heron diet did not change significantly during the fledging period of their juveniles. The calculated trophic levels of Great Cormorants and Grey Herons were similar (3.55 ± 0.12 and 3.57 ± 0.41, respectively). The isotopic values in Grey Herons and Great Cormorants were 14.6–16.0‰ for δ15N and –27.3–(–24.9)‰ for δ13C. These values are typical of piscivorous bird species mostly feeding in freshwater bodies, i. e. in the Curonian Lagoon. The δ15N values found in the feathers of Long-tailed Ducks ranged from 7.7 to 13.9‰ and the δ13C values ranged from –33.6 to –24.9‰ showing high variation of feeding habitats during the moulting period: from freshwater to marine environment.

Stable isotope tracing of trout hatchery carbon to sediments and foodwebs of limestone spring creeks

Limestone springs support productive ecosystems and fisheries, yet aquaculture may modify or impair these ecosystems. We determined trout hatchery organic contribution to spring creek sediments and foodwebs with natural abundance stable isotope methods. Hatchery feed, waste, and trout were significantly enriched in δ 13C relative to autotrophs and wild fish. Spring creek sediments were enriched in δ 13C toward the hatchery endmember relative to reference streams without hatcheries and relative to a larger larger-order, spring-influenced stream. Contribution of hatchery C to spring creek sediments was greatest during March and associated with greatest sediment %C. Contribution of hatchery C to pollution-tolerant isopod diet was 39–51% in a stream receiving limestone spring water via hatchery effluent. Isopods of one spring creek also relied on hatchery-derived C within one month of hatchery closure. Four years later, less pollution pollution-tolerant amphipods dominated and consumed non-vascular over vascular autotrophs (86%). Isopods of a second spring creek with an active hatchery did not appear to be using hatchery matter directly, but were enriched in δ 34S relative to a spring creek tributary with no hatchery influence. Isopods in both of these streams were relatively enriched in δ 15N, indicating general nutrient enrichment from surrounding agricultural land use. The contribution of hatchery vs. wild fish in diet of herons and egrets was traced with δ 13C of guano. These birds were strongly dependent on stocked trout in a spring creek with a recently closed state trout hatchery, and also near another large, state-run hatchery. Heron dependence on hatchery fish in the spring creek decreased with time since hatchery closure. Use of stable isotope natural abundance techniques in karst spring creeks can reveal stream impairment due to aquaculture, specific C sources to bio-indicating consumers, losses of farmed fish to predation, and potential exposure of higher order consumers to contaminants associated with aquaculture.

Seasonal Diet of the Grey HeronArdea cinereaon an Oceanic Island (Tenerife, Canary Islands): Indirect Interaction with Wild Seed Plants

A total of 7 460 prey items were counted in the 199 pellets analysed, of which 96.2% corresponded to arthropods. Aeshnidae larvae (Odonata) made up 66.1% of total prey items and were the main invertebrate group. Vertebrates constituted 3.8%, while reptiles and mammals were the main prey (1.8%, respectively). Despite the small size of the invertebrates, this group reached > 60% in terms of biomass. All main prey items varied significantly among seasons. Odonata was the most important group for all seasons, reaching its maximum value in summer. In the case of vertebrates, reptiles were mainly captured in spring and mammals in winter. With regards to indirect interaction with seeds, a total of 901 seeds associated with lizard remains were found in 77 pellets; indicating that they were previously consumed by these reptiles. External visual damage of seeds was low and only 1.1% was destroyed. No seeds germinated after the four month germination experiment and practically all of them were unviable. In conclusion, these results indicate that Grey Heron diet on islands varies in comparison with continental zones, includ- ing an important number of invertebrates and reptiles. Furthermore, this bird acts as an opportunistic secondary seed disperser, although its ecological effect does not seem to be very significant for the dynamics of the Canarian ecosystems.

Selective Foraging of Grey Heron (Ardea cinerea) in Relation to Density and Composition of the Littoral Fish Community in a Submontane Dam Reservoir

Abstract Grey Herons foraged in a high number only in one of three preferred foraging areas in the Dobczyce Reservoir, S. Poland: (1) the backwater area at the main tributary inlet (MTI), (2) the shore of the near-dam pool (NDP), and (3) shallow lateral bay (SLB). Median value of the fraction of herons foraging in MTI was 64% of all counted in the reservoir in 2001-2002 despite the smallest fish density there (2 times smaller than in NDP, and by one order of magnitude than in SLB). Roach (Rutilus rutilus) was the most abundant both in the heron diet (13 species) and in littoral fish communities (8 species). Total length of prey ranged within 4.2-26.5 cm. The individual size range of littoral fish was similar (4.6-31.5 cm). However, the size distributions in three foraging areas and in heron diet were different. Fish longer than the median total length of heron prey, i.e. ≥8 cm in total length constituted 51.9% of heron diet, 34.7% of the fish community in MTI, 8.5% in the psammolittoral of NDP, and only 5...

The Response of the Grey Heron to a Rapid Increase of the Round Goby

Abstract The fish community of the Gulf of Puck in the Baltic Sea has changed in recent years following the successful introduction of the Round Goby (Neogobius melanostomus). The first specimen of Round Goby was caught in 1990 and now is estimated in millions of individuals. The Round Goby was a main component of the Grey Heron diet in the colony at Mosty and made up 95% of regurgitated prey items. During chick rearing period, herons mostly flew to the coast to forage in shallow waters and feed on the Round Goby. The numbers of Grey Herons at Mosty have increased recently, especially since 1999 (from 238 in 1999 to 493 nests in 2003; an increase of 107%). The indirect evidence suggests that the rapid expansion of the Round Goby has influenced the Grey Heron and affected both the diet and the numbers of birds feeding and breeding in the vicinity of the Puck Gulf.

Wading Bird Depredations on Channel Catfish Ictalurus punctatus in Northwest Mississippi

Abstract.We interviewed farm managers about their perceptions of wading bird problems and conducted preliminary surveys of wading bird populations at 67 randomly selected channel catfish Ictalurus punctatus pond complexes in northwest Mississippi during December 1995. At a subsample of 24 complexes and 10 other complexes previously surveyed in 1990, we surveyed wading bird populations bimonthly throughout the year in 1996 and observed great blue herons Ardea herodias and great egrets Ardea alba feeding at catfish ponds. Seventy‐five percent of farm managers questioned felt that wading birds were causing losses to their fish stocks, and 74% believed the problem was increasing. Consistent with interview results, 88% of the pond complexes surveyed had one or more wading birds present. Despite reported harassment programs by producers, great blue heron densities at 10 complexes previously surveyed in 1990 had increased by more than eightfold in 1996. Great blue heron densities varied with location, season and time of day, but the average 127‐ha farm supported about 78 herons and 56 great egrets. Despite similar populations, the potential impact of these two species was quite different. Live catfish, averaging 10.3 cm in length (circa 10 g) comprised only 8% of the egret diet by weight, and most of the fish were obtained from fingerling ponds during periods when these fingerlings may be weakened by the bacterial disease, enteric septicemia of catfish. In contrast, live catfish, averaging 16 cm in length (circa 34 g), comprised 44% of the great blue heron diet by weight. Herons foraged from both fingerling and food fish ponds, primarily in the early morning and evening. Based on average population densities and foraging rates, herons at the average 127‐ha farm in northwest Mississippi consumed 114,000 (circa 3,900 kg) catfish, annually. However, further studies are recommended to document production losses.

Analysis of pellets of the Grey heron, Ardea cinerea, from colonies in Belgium

Analyses of the contents of pellets of Grey herons from different breeding colonies and breeding seasons indicated that the mammal and invertebrate species included in the heron diet varied between colonies and between years. The large differences in mammal species found in neighbouring heronries suggested the existence of important small‐scale variability in the exploitation of mammals. Almost no fish and bird remains were found in the pellets. We believe that most invertebrates, even the smallest ones, were actively taken by the herons. Identification of mammal species composition by means of skulls and hair remains gave different results. The shape of a pellet seemed to be dependent upon the (moisture?) conditions during its formation.