Factors affecting shorebird hatching outcomes at the Ashley River/Rakahuri-Saltwater Creek estuary, New Zealand

We studied comparative microhabitat use by breeding Kelp Gull (Larus dominicanus) and the threatened Olrog's Gull (Larus atlanticus) at six colonies through the distributional range of Olrog's Gull in coastal Patagonia, Argentina. The ranges of values for most of the 13 microhabitat variables measured (related to vegetation, soil and topography) were broader for the Kelp Gull than Olrog's Gull, with those of that latter within the range of Kelp Gull, indicating potential spatial conflict between the two species. There was particular overlap in nest-site characteristics, but differences were observed between the two species. Multivariate analyses showed that the most important differences in habitat between the two species related to vegetation cover and distance to the high-tide line. Compared with Kelp Gulls, Olrog's Gulls placed their nests in sites with lower proportion of vegetation cover, lower percentages of silt-clay in the substrate, and closer to the high-tide line. For both species the patterns of nest-site selection did not vary among colonies, although the extent of differences between the two species varied with availability of habitat at each colony. Although Olrog's Gulls started laying 12–14 days earlier than the larger Kelp Gulls, the latter occupied breeding colonies earlier and may, therefore, interfere with settlement of Olrog's Gulls. Considering the increase in the numbers, colony area and nesting density of Kelp Gulls currently observed in coastal Patagonia, there is an urgent need to implement monitoring programs for both species and conduct studies to better predict the results of their interactions.

Nest site selection of Kelp gulls Larus dominicanus breeding in Conejo and Bridges islands, Tierra del Fuego, Argentina, was assessed between 14 and 30 December 2005 to describe variability in nest site features and determine variables affecting nest choice. Fourteen microhabitat variables were quantified at 40 nest sites and at 40 random points in each island during the late incubation stage. Nests at the two colonies were placed on different kinds of substrates across areas with varying degrees of cover provided either by rocks or vegetation. Despite the variability observed in nest site features, rock cover and rocky substrates were the main factors determining nest site selection. At Conejo Island, nest sites presented more rock cover, less percentage of vegetation cover and of vegetation debris substrate, and were placed further from the nearest vegetation in comparison to random points. Similarly, gulls at Bridges Island selected nest sites with more rock cover which were placed mainly on rocky and vegetation substrates. This contrasts with results previously obtained in Argentina, which indicated that vegetation is a key factor influencing Kelp gull nest site selection. Over 80% of the nests at both study colonies were placed on the northern slopes of the islands, relatively more protected from the strong prevailing southwest winds, and nests at both colonies tended to be more protected on their southern side either by rocks or vegetation. Results obtained at Tierra del Fuego confirm the plasticity of microhabitat use by Kelp gulls, and their ability to take advantage of nesting sites according to availability and local environmental factors.

Breeding success of African Black Oystercatchers (Haematopus moquini) was monitored over three austral summers on Robben Island, South Africa from 2001 to 2004. Robben Island is a busy tourist destination which has a resident population that live and work on the island in addition to tourists that visit the island daily. Potential predators of birds’ eggs and chicks include feral cats (Felis catus), Kelp Gulls (Larus dominicanus), Mole Snakes (Pseudaspis cana) and House Rats (Rattus rattus). The mean number of fledglings per pair declined from 0.74 in the first breeding season to 0.41 and 0.35 in the subsequent breeding seasons. This fledgling success slightly exceeded the threshold estimated to maintain a stable population, and is similar to fledging success observed in other oystercatcher species. The lower fledging success in the second and third breeding seasons compared to the first breeding season were increased depredation of eggs and chicks and high-tide events on 17 February 2003 and 10 February 2004. Predation can be aggravated by human disturbance, and it was found that the area with greatest resident and tourist activity had the greatest egg and chick losses in all three breeding seasons. The area adjacent to the disturbed area had reduced breeding success in the second breeding season, possibly a result of increased predation associated with the settlement. Breeding success near the Kelp Gull breeding colony decreased in the third breeding season; the period during which the greatest number of Kelp Gulls were breeding. The potential success of a breeding attempt decreased if incubation of the clutch started later in the breeding season.

Consequences of Nest Desertion and Inattendance for Magellanic Penguin Hatching Success

We examined microhabitat preferences and their adaptiveness for the kelp gull Larus dominicanus in one of its largest colonies in Patagonia. We quantified 13 habitat variables at 104 and 92 nest‐sites and at 70 and 60 random points in 1998 and 1999, respectively. We recorded egg laying dates, hatching success, number of chicks fledged and breeding success at 92 of these nests in each of the study seasons. Compared to random points, nest sites had more vegetation cover and were closer to the nearest available bush, but they were located further from the nearest clearing for flight take‐off, all variables included in the “vegetation” principal component. Nests were built on substrates with lower slopes and higher percentages of silt‐clay, but with lower percentages of rock. In both years, hatching success, number of chicks fledged and breeding success were related positively to the vegetation principal component. Substrate slope and composition contributed to explain the variation in hatching and breeding success in 1998 and 1999, respectively. Our study shows that some kelp gull breeding parameters are affected by nest‐site habitat characteristics. These associations were in most cases influenced by the timing of breeding, with earlier breeders being more successful. Vegetation effects and substrate characteristics were important variables in distinguishing random sites from nest sites, and in explaining variation in breeding performance, showing that their habitat preferences are adaptive and allowing us to detect both the pattern and process in kelp gull habitat selection.

Interactions between breeding gulls and monofilament lines at one of the main recreational fishing sites in Argentina

We evaluated discard consumption by Kelp Gulls (Larus dominicanus) and Black-browed Albatrosses (Thalassarche melanophrys) associated with trawlers operating at Golfo San Jorge, Argentina, and assessed differences in their feeding behaviour, prey size preferences and foraging efficiency. Observations were made onboard hake (January 2007) and shrimp vessels (November 2008). The Kelp Gull and Black-browed Albatross were the most frequent and abundant seabirds at both fisheries, while Argentine Hake (Merluccius hubbsi) dominated the composition of discards. Kelp Gulls and Black-browed Albatrosses consumed 91% of experimentally discarded hake (n = 1236). Mean sizes of prey consumed by gulls were 22.4 and 23.7 cm in the hake and shrimp fisheries, respectively, while those of prey consumed by albatrosses were 28.5 and 31.3 cm, respectively. In both fisheries, gulls selected the smaller prey available ( 25 and >30 cm in hake and shrimp fisheries, respectively). Intraspecific and interspecific kleptoparasitism were significantly more frequent than expected in Kelp Gulls and Black-browed Albatrosses, respectively. Robbing efficiency was clearly higher in albatrosses than gulls. In both species, sizes of prey consumed by direct capture were significantly smaller than those stolen, and the rate of kleptoparasitism increased with prey size. Gulls stole significantly smaller prey than albatrosses. Prey selection by Kelp Gulls is affected by the interaction with Black-browed Albatrosses, and the degree at which discards are used by both species appears to depend on the fishery considered, the food on offer and the selection of prey sizes according to seabird species-specific preferences.

Wetland birds on 11 rivers of the Upper Waitaki Basin, South Island, New Zealand were surveyed annually between 1991 – 1994. Diversity, minimum abundance and density of birds were compared. In total 26 species of wetland birds were recorded. Minimum estimated river bird numbers were: 3566 Black-backed Gulls (Larus dominicanus), 3302 Black-fronted Terns (Sterna albostriata), 3260 Banded Dotterels (Charadrius bicinctus), 793 Black-billed Gulls (Larus bulleri), 789 Wrybills (Anarhynchus frontalis), 788 South Island Pied Oystercatchers (Haematopus ostralegus), 421 Pied Stilts (Himantopus himantopus), 85 Black Stilts (Himantopus novaezelandiae), 51 Caspian Terns (Hydroprogne caspia), and 3680 waterfowl and cormorants. Densities of birds ranged from 0.17 birds ha-1 on the Pukaki River to 0.95 birds ha-1 on the Lower Ohau River. The Cass, Lower Ohau, Godley, Tekapo and Ahuriri Rivers had higher densities of one or more species than the Upper Ohau and/or Pukaki Rivers. Densities of Black-fronted Terns, Black Stilts, Pied Stilts and Caspian Terns were negatively correlated with altitude, and in general birds preferred river sections with low or moderate flows, and low or moderate vegetation cover. Eight of the 11 rivers surveyed had more than 1% of estimated total populations of one or more of three globally vulnerable or endangered species, and in combination rivers of the Upper Waitaki Basin support almost all known Black Stilts, 15% of all Wrybills and 32% of all Black-fronted Terns. We suggest that the Upper Waitaki Basin may now provide half of all remaining suitable braided river bird habitat in New Zealand.

Seabirds frequently nest in mixed-species colonies (Burger 1985). Several studies have shown differences in habitat and nest-site use among seabirds (Buckley and Buckley 1980, Croxall and Prince 1980, Fasola and Canova 1992). However, some degree of overlap in habitat and nest-site requirements may exist between species, resulting in interspecific competition that often leads to nest-site displacement or even the replacement of one species by another (Buckley and Buckley 1980, Burger 1985). Spatial interactions between seabirds can be more intense in areas where habitat is limited or when the population of one of the species is expanding (Burger and Shisler 1978, Trivelpiece and Volkman 1979, Duffy 1983, Ainley 1990). At many mixed colonies of larids, larger species often displace smaller species from their territories, occasionally forcing them to abandon the breeding area (Burger and Shisler 1978, Burger 1985). In addition, larger larids generally arrive at breeding sites earlier (Morris and Hunter 1976, Burger 1985), which gives them a competitive advantage over smaller species. Gulls (Larus spp.) frequently have been involved in the displacement of other species from breeding habitats (Thomas 1972, Burger 1979, Bradley and Monaghan 1986, Furness and Monaghan 1987). Terns appear to be one of the most affected seabirds, and some tern populations have decreased as a result of population expansion by gulls (Thomas 1972, Nisbet 1973, Greenhalgh 1974, Courtney and Blokpoel 1983, Parnell et al. 1988, Ainley and Hunt 1991, Blokpoel and Scharf 1991). At Punta Le6n, Argentina, Royal Terns (Sterna maxima) and Cayenne Terns (S. eurygnatha) breed intermingled in a dense cluster of nests within a Kelp Gull (Larus dominicanus) colony. The Kelp Gull colony increased in size from 3,200 pairs in 1982 to 6,500 in 1995, and gulls currently occupy almost all of the available nesting space (Yorio et al. 1994). Given the overlap in nest-site use and the current expansion of Kelp Gulls, we expected that competition for nesting space could result in negative effects on both species of terns. In this paper, we document spatial interactions between Kelp Gulls and Royal and Cayenne terns at Punta Le6n, Patagonia. We

A total of 1,177 lice of four species were collected from 124 kelp gulls (Larus dominicanus) and 137 lice of the same four species from 60 Franklin's gulls (Larus pipixcan). The louse Saemundssonia lari (O Fabricius) (Phthiraptera: Philopteridae) was the most numerous on both gull species, with infestation rates of 4.9 on kelp gulls and 1.8 on Franklin's gulls. The second most abundant louse was Quadraceps punctatus (Burmeister), with a high infestation rate but low prevalence on kelp gulls; those parameters were much lower among lice from Franklin's gulls. The composition and community structure of the lice were similar on both host species, but not their infestation rates. In addition, the feather mite Zachvatkinia larica Mironov (Acari: Avenzoariidae) is recorded from kelp gulls and Franklin's gulls for the first time, while the gamasid mite Larinyssus sp. is recorded from kelp gulls, also for the first time. The population parameters of all species of ectoparasites are discussed.

Year-round use of anthropogenic food sources in human modified landscapes by adult and young Kelp Gulls

The southern black-backed gull (Larus dominicanus) is a common species throughout New Zealand, and has a significant presence in Auckland City. Large colonies are present on Rangitoto Island only 8 km from the city’s centre. The proximity of these colonies to the anthropogenic resources of the city may have influenced breeding locations and local populations. Using field data from the 2012/13 breeding period, we compare the current status of the breeding population on Rangitoto Island with historical data collated from literature. The Rangitoto population exhibited rapid growth throughout the early 20th century, a pattern attributed to environmental changes associated with European settlement and development. Since the 1980s, the colony sizes have declined, a change that is consistent with other gull populations both nationally and globally. The driver of the population changes is likely to be the availability of food and the expansion of vegetation into the colonies. Human disturbance and predation are discounted as impacting on population change.

During five reproductive seasons, we documented the presence, extent and origin of perineal wounds in South American fur seal pups (Arctocephalus australis) on Guafo Island, Northern Chilean Patagonia. The seasonal prevalence of perineal wounds ranged from 5 to 9%, and new cases were more common at the end of the breeding season (February), when pups were on average two months old and were actively expelling hookworms (Uncinaria sp). Histologically, wounds corresponded to marked ulcerative lymphoplasmacytic and histiocytic dermatitis with granulation tissue and mixed bacterial colonies. In 2015 and 2017, kelp gulls (Larus dominicanus) and dolphin gulls (Leucophaeus scoresbii) were observed picking and wounding the perineal area of marked pups. This behaviour occurred more frequently after the pups' defecation, when sea gulls engaged in consumption of pups' faeces. The affected pups usually had moderate to marked hookworm infections along with bloody diarrhoea and anaemia. Pups with severe wounds (23% of affected animals) had swollen perineal areas and signs of secondary systemic bacterial infection. We propose that seagulls on Guafo Island have learned to consume remains of blood and parasites in the faeces of pups affected by hookworm infection, causing perineal wounds during this process. We conclude that this perineal wounding is an unintentional, occasional negative effect of an otherwise commensal gull–fur seal relationship.

We analyzed habitat requirements and selection of Kelp Gulls (Larus dominicanus) breeding at 68 colonies along 2,500 km of coastline in Patagonia, Argentina. Kelp Gulls use a wide range of nesting habitats that include areas with shrub, grass, and herbs which provide different degrees of cover; open ground of various substrate types; and slopes of widely different gradients, confirming the plasticity of the species with respect to habitat recorded elsewhere in the Southern Hemisphere. Eighty percent of the colonies were on islands, the probability of occupation of which increased with distance from mainland and availability of vegetation. Vegetation cover was a key component of nesting habitat for Kelp Gulls in Argentina. Gulls occupied areas with higher cover than random areas; but within vegetated areas, they showed preference for sparser cover that increased visibility and facilitated escape. Kelp Gulls often nested with other species of seabirds and seals and had a positive association with the Olrog's Gull (L. atlanticus).

The introduction of species can have negative effects on species, communities, and ecosystems, although native predators may profit from the introduced prey. We present an evaluation of the consumption of the introduced Green Crab (Carcinus maenas) by Kelp Gulls (Larus dominicanus) during the austral winter in Patagonia, Argentina. Green Crab remains were present in 9.4% (n = 416) of the Kelp Gull pellets collected between June and August of 2021, at four coastal sectors distributed along more than 400 km of coastline. Frequency of occurrence of Green Crabs in Kelp Gull pellets varied between 0 and 66.7% depending on the location, and being similar for the three studied months. Overall, Kelp gulls included at least 35 food items in their diet with variable contributions from different food categories, again depending on the location. This is the first report on the winter consumption of Green Crabs by Kelp Gulls and provides baseline information for understanding the role of this introduced species in newly invaded coastal ecosystems.