Gull Colonies Research Articles

21 000 birds in 4.5 h: efficient large‐scale seabird detection with machine learning

AbstractWe address the task of automatically detecting and counting seabirds in unmanned aerial vehicle (UAV) imagery using deep convolutional neural networks (CNNs). Our study area, the coast of West Africa, harbours significant breeding colonies of terns and gulls, which as top predators in the food web function as important bioindicators for the health of the marine ecosystem. Surveys to estimate breeding numbers have hitherto been carried out on foot, which is tedious, imprecise and causes disturbance. By using UAVs and CNNs that allow localizing tens of thousands of birds automatically, we show that all three limitations can be addressed elegantly. As we employ a lightweight CNN architecture and incorporate prior knowledge about the spatial distribution of birds within the colonies, we were able to reduce the number of bird annotations required for CNN training to just 200 examples per class. Our model obtains good accuracy for the most abundant species of royal terns (90% precision at 90% recall), but is less accurate for the rarer Caspian terns and gull species (60% precision at 68% recall, respectively 20% precision at 88% recall), which amounts to around 7% of all individuals present. In sum, our results show that we can detect and classify the majority of 21 000 birds in just 4.5 h, start to finish, as opposed to about 3 weeks of tediously identifying and labelling all birds by hand.

Maternal transfer and occurrence of siloxanes, chlorinated paraffins, metals, PFAS and legacy POPs in herring gulls (Larus argentatus) of different urban influence

Urban herring gulls (Larus argentatus) are exposed to contaminants from aquatic, terrestrial and anthropogenic sources. We aim to assess if differences in urbanisation affect ecological niche and contaminant concentrations in female herring gulls. Furthermore, we investigated maternal transfer from mothers to eggs for all the target compounds, including chlorinated paraffins (CPs) and cyclic volatile methyl siloxane (cVMSs), which to our knowledge have not been assessed in herring gulls previously. We compare concentrations of legacy and emerging contaminants and metals in blood and eggs between two herring gull colonies located 51 km apart, in the urban influenced Norwegian Oslofjord. While both colonies are within an urbanised area, the inner fjord is more so, as it is surrounded by Oslo, the capital and largest city in Norway Stable isotopes of carbon and nitrogen indicated a more marine ecological niche in the outer than the inner fjord colony, although with overlap. Persistent organic pollutant (POP) concentrations were similar in the inner and outer fjord colonies, while the short-chained chlorinated paraffins (SCCP), which are recently added to the Stockholm convention and contaminants of emerging concern (CECs) varied, with higher concentrations of SCCP and the cVMS decamethylcyclopentasiloxane (D5) in females and eggs of the inner fjord colony. Per- and polyfluorinated substances (PFAS) concentrations were higher in the outer fjord colony, likely linked to releases from a point-source (airport and waste management facility with open access to food waste). In blood, chlorinated paraffins contributed most the total lipophilic contaminants (inner: 78%, outer: 56%), while polychlorinated biphenyls (PCBs) were the most abundant lipophilic contaminants in eggs (inner: 62%, outer: 46%). Dechloranes and brominated flame retardants (BFRs) were detected in few samples. Maternal transfer, assessed by egg to blood ratios, of cVMSs were similar to the POPs with mean log ratio 0.39 (D5), while it was lower for SCCPs, with log ratios-0.77. Our results indicate comparable POP exposure of the herring gulls in the inner and outer Oslofjord, likely due to overlap in ecological niches between the colonies and wide distribution of POPs. The differences between the colonies in concentrations of PFAS, cVMS and CPs shows that point source exposures and urban influence may be more important than ecological niche for these compounds.

Seabird colonies as the main source of nutrients for the coastal ecosystems in the Atlantic Islands of Galicia National Park (NW Spain)

Seabirds form large colonies during the reproductive period, producing substantial changes in coastal ecosystems. The present study quantifies the amount of N and P deposited in colonies of yellow-legged gull (Larus michahellis) in the Atlantic Islands of Galicia National Park (AINP). Based on the composition of droppings, the amount of total N (TN), total P (TP) and bioavailable P (Pbio) deposited directly on the area occupied by the colony was determined. In addition, the amount of NH3 released into the atmosphere was also estimated by applying a bioenergetic model. The results indicated that 5.35 t total N, 3.35 t total P and 1.24 t bioavailable P are deposited in the colony annually. The archipelagos that received the greatest amount of nutrients were the Cíes Islands (2.37 t TN y−1, 1.48 t TP y−1, 0.55 t Pbio y−1), Sálvora (1.94 t TN y−1, 1.22 t TP y−1, 0.55 t Pbio y−1) and Ons (1.04 t TN y−1, 0.65 TP y−1, 0.24 t Pbio y−1). Rainwater from the colonies showed higher values of nutrients than in the control plot, possibly also due to gull influence. Therefore, the yellow-legged gull colony seems to be the most important source of nutrients at a local level, exerting a clear influence on the N and P cycles in this National Park. Another aspect worth taking into consideration is that increased N and P bioavailability may have a negative effect on the conservation of rare or threatened habitats and species by promoting the expansion of non-native ruderal species.

Density-dependence of nestling immune function and physiological condition in semi-precocial colonial bird: a cross-fostering experiment

BackgroundNesting in large aggregations provides several important advantages for colonially breeding birds. However, it also imposes certain costs, associated with facilitated pathogen transmission and social stress. The cost-benefit ratio is not similar for all the birds in a colony and it might be mediated by nest density. To investigate the influence of nest density on cell-mediated immune function and on physiological condition of nestlings, we arranged a cross-fostering experiment in three breeding colonies of black-headed gulls Chroicocephalus ridibundus. First, we exchanged eggs between plots of high and low nest density. Afterwards, we performed phytohaemagglutinin (PHA) skin test and we measured blood haemoglobin concentration in nearly 350 nestlings from experimental (exchanged) and control (non-exchanged) groups.ResultsWe found that PHA response was lowest in high nest density control group, indicating that depressed immune function of offspring, likely caused by social stress, can be considered as a cost of colonial breeding. Contrastingly, body condition of nestlings was the poorest in low density control group.ConclusionNestlings hatched and raised in high nest density plots did not have higher blood haemoglobin concentration in comparison to other study groups. Furthermore, they were affected with depressed cell mediated immune function, which is possibly driven by combined maternal (corticosteroid hormones deposited in yolk) and environmental (elevated social stress) effects. These results indicate that breeders from high nest densities do not benefit by rising offspring in better quality, in terms of immune function and body condition, although, in the light of previous studies, high nest densities are occupied by birds of higher individual quality, than low density areas. Our study provides a novel insight into the mechanisms of density-dependence that govern fitness of colonially nesting birds.

Effects of a yellow legged gull (Larus michahellis) colony on soils and cliff vegetation in the Atlantic Islands of Galicia National Park (NW Spain)

Seabirds are powerful environmental modulators, generating major changes in soil properties and vegetation in areas where their breeding colonies are established. One of the largest yellow-legged gull colonies in the world is found in the Atlantic Islands of Galicia National Park. In this study, we performed seasonal monitoring, over a period of 5 years, of the flora and soil in eight subcolonies characterized by different densities of gulls. Soil nutrient concentrations differed significantly between the control site and the subcolonies, as well as between seasons; the concentrations of N-NO3- and bioavailable P were highest in samples obtained at the end of the breeding season. Principal Component Analysis (PCA) transformed the environmental variables into three main components following varimax rotation. The PCA components were used as potential predictors in distance-based Redundancy Analyses (db- RDA) to explain turnover and also nestedness patterns in plant assemblages. Species turnover was explained by both natural (salinity) and nutrient gradients, while none of the relationships were significant in the nestedness analysis. Floristics inventories clearly revealed ruderalization of vegetation in the densest subcolonies, which led to total replacement of the most representative vascular plant species by eutrophic and ruderal species. PERMANOVA analysis showed that seagull density in 1991, when the seagull population was at its highest, could be used to group similar plant assemblages; however, this relationship was not observed for seagull density in 2011, which was 70–90% lower than in 1991. The study findings indicate that the environmental effects of seabird colonies are long lasting and that disappearance of the birds does not lead to restoration of the previous vegetation. The gull colony has irreversibly transformed the soil and vegetation of cliffs, generating a new environmental system.

Stress in the egg makes gull chicks fitter

Biologists have known for years that conditions experienced during early development can dramatically influence health and longevity through to adulthood. When the environment becomes persistently challenging or too unpredictable, mothers pass on the stress hormones produced in response to difficult conditions to their offspring developing in the womb or egg. It is commonly believed that these increases in stress exposure have detrimental consequences for developing creatures long into their futures, such as the increased risk of illness and reduced survival. However, the stress communicated to a developing embryo by its mother could also be an advanced warning, which helps the youngster to develop in ways that might improve its chances of survival later in life. In new research led by Jose Noguera and his team at the University of Vigo, Spain, they provide evidence suggesting that this might be the case.Noguera and colleagues headed out to Sálvora Island, off the Atlantic coast of northern Spain to study a wild breeding colony of yellow-legged gulls. The team stealthily monitored the birds as they laid their eggs and selected the first egg from 46 nests – the first laid egg is often the only one that hatches successfully – before injecting some with a stress hormone, corticosterone. Soon after the chicks hatched the researchers took a small blood sample to investigate how the hormone boost had affected the developing chicks by looking at the DNA packaged in the birds’ red blood cells. Knowing that the ends of each DNA chromosome are tipped with specialised structures, telomeres, which protect them from wearing down and generally shorten with age, the team decided to find out how the stress hormone in the chick's eggs affected the length of the telomeres. In addition, the team checked the enzyme, telomerase, which is responsible for building and maintaining telomeres, to find out how well prepared the youngsters were for the rigours of life after hatching.The researchers found that the chicks that were exposed to stress hormones as eggs had more active telomerase and longer telomeres compared to the chicks that had not received a corticosterone boost. These results suggest that increased exposure to stress during embryonic life leads to changes that might improve the chicks’ survival prospects. Interestingly, using data collected previously from the same population of gulls, they also showed that starting life after hatching with longer telomeres increases the chances of chicks surviving for at least up to 8 days. This time window corresponds to the period of highest mortality in this species as gull chicks face constant danger, competing with their siblings for food while predators lurk in the colony.Noguera's study suggests that maternally derived stress hormones may be a key mechanism through which mothers transmit valuable signals to their offspring that could help them to program their biology in preparation for life on the outside. More broadly, the team challenge the common view that increased levels of stress hormones in the egg inevitably incur costs for the developing chick as a consequence of poor maternal conditions. It seems, instead, that the mother's stressful gift to her offspring may provide an opportunity to make them fitter, at least during the earliest and most challenging stages of life.

Long-eared Owl Asio otus breeding in a Caspian Gull Larus cachinnans colony: Reversed roles in protective nesting association?

We describe the event of Long-eared Owls Asio otus nesting on an island within a colony of Caspian Gulls Larus cachinnans at the Mietków Reservoir (SW Poland). The owls nested in an old (possible corvid) nest in a willow and raised two owlets. They probably did not hunt gulls, neither adults nor chicks. We suggest that, in this case, the Long-eared Owls benefitted from breeding within a gull colony because of the added security against predators that the gulls provided.

The MallardAnas platyrhynchosin Slovenia: a review with an estimation of its current population

AbstractAlthough the Mallard is one of the most numerous and best-studied waterbirds in the world, it received almost no attention in Slovenia. It is one of the most frequently observed waterbirds in our country, with frequency often reaching 100%. Sites with lower frequency either freeze in winter or have a low number of individuals to start with. The Mallard is also the most dominant species (17.5% and 89.0%) with higher dominance at sites less suitable for waterbirds due to the lack of available shoals. Mallards reach their maximum numbers during fall migration and winter. Spring migration has no discernible peak and has been significant only for Lake Cerknica. On shallow waters, the maximum is reached in August and September, a month before fall migration begins, indicating local movement to food-rich sites. Females make up only 36.7% of the observed Mallards and reach the maximum proportion (41.5%) in winter and the lowest in April and May (14.7%), when they nest. The breeding season in Slovenia lasts from mid-January to early December, with the majority of females rearing broods from April to July. Average brood size is 6.2 ± 2.66 and declines with season, age of young and altitude. It varies between habitat types and is highest on Treatment and Coastal Wetlands (7.3) and lowest on deep waters such as Reservoirs (5.7) and Lakes (5.6). No really high breeding densities were found in Slovenia and were similar to those in other countries. Breeding densities are higher on smaller Ponds (< 8 ha), on sites with isolated islands and breeding colonies of gulls and terns (e.g. Lake Ptuj). Breeding density also decreases with elevation. Slovenian breeding population is estimated at 1,473–3,763 bp and wintering population averages 22,237 (10,376–32,010) individuals. Data suggest a decline in the wintering population most likely due to warmer winters. The majority of Mallards winter in NE Slovenia, where eight of eleven sites have a maximum of more than 1,000 Mallards. Most Mallards winter on the Drava river with Ptuj and Ormož lakes, where the highest numbers of Mallards were also recorded (Lake Ptuj: 8,330 ind., Lake Ormož: 5,400 ind.). The highest number of individuals during spring migration was recorded on Lake Cerknica (4,581) and during autumn migration on Medvedce reservoir (3,379). Apart from standing waters, the highest density of wintering Mallards is found in urban sections of slow-flowing rivers, probably due to higher safety and food availability.72,731 Mallards were hunted between 2001 and 2018, mainly in NE Slovenia (28% in the Pomursko hunting management district). The number of Mallards hunted is declining in all hunting areas and has declined by 64% since 2001 and even more since the 1990s. According to hunt data, hunting is by far the most important cause of the Mallard mortality in Slovenia (97.4%), followed by predation (1.1%). The Mallard mortality in Slovenia is largely unstudied and natural mortality is most likely underestimated, not only because it does not include mortality in the pre-fledging period, a period with the lowest survival, but also because the detectability of natural mortality is considerably lower. In contrast to the hunted numbers, there have been only nine recoveries of ringed individuals from abroad in the last 100 years, suggesting that hunters may not be reporting recoveries to the ringing centre. Apart from the 1972–1975 period, when 87% of Mallards were ringed, the intensity of ringing of Mallards in Slovenia is low, resulting in only seven Mallards recovered abroad. The longest distance of a Mallard ringed in Slovenia comes from Ukraine (1,290 km), while the longest distance between ringing and recovery sites is 2,075 km from an individual ringed in Finland. The only colour morphs documented in Slovenia are Mallards with paler feathers, attributed to one of the colour aberrations resulting from lower melanin productivity. Only few hybrids and mixed pairings with other wild duck species were observed.

Evaluating Functional Dispersal in a Nest Ectoparasite and Its Eco-Epidemiological Implications.

Functional dispersal (between-site movement, with or without subsequent reproduction) is a key trait acting on the ecological and evolutionary trajectories of a species, with potential cascading effects on other members of the local community. It is often difficult to quantify, and particularly so for small organisms such as parasites. Understanding this life history trait can help us identify the drivers of population dynamics and, in the case of vectors, the circulation of associated infectious agents. In the present study, functional dispersal of the soft tick Ornithodoros maritimus was studied at a small scale, within a colony of yellow-legged gulls (Larus michahellis). Previous work showed a random distribution of infectious agents in this tick at the within-colony scale, suggesting frequent tick movement among nests. This observation contrasts with the presumed strong endophilic nature described for this tick group. By combining an experimental field study, where both nest success and tick origin were manipulated, with Capture-Mark-Recapture modeling, dispersal rates between nests were estimated taking into account tick capture probability and survival, and considering an effect of tick sex. As expected, tick survival probability was higher in successful nests, where hosts were readily available for the blood meal, than in unsuccessful nests, but capture probability was lower. Dispersal was low overall, regardless of nest state or tick sex, and there was no evidence for tick homing behavior; ticks from foreign nests did not disperse more than ticks in their nest of origin. These results confirm the strong endophilic nature of this tick species, highlighting the importance of life cycle plasticity for adjusting to changes in host availability. However, results also raise questions with respect to the previously described within-colony distribution of infectious agents in ticks, suggesting that tick dispersal either occurs over longer temporal scales and/or that transient host movements outside the breeding period result in vector exposure to a diverse range of infectious agents.

Yellow-legged gull eggs (Larus michahellis) as persistent organic pollutants and trace metal bioindicator for two nearby areas with different human impact

The concentration of different persistent organic pollutants (POPs including chlorinated and brominated compounds) and trace metals and metalloids (As, Cd, Cu, Cr, Pb, Hg, Ni, and Zn) was examined in eggs from two colonies of yellow-legged gulls. The two colonies are established in Ría de Vigo, Northwest Spain, with a distance between them of only 10 km, one in Vigo town (industrial and harbour activities) and the other in the Cíes Islands in a Natural Park and Marine Protected Area –MPA- (with no known anthropogenic inputs). Statistically significant differences for the two colonies were observed for Hg, the sum of 7 CBs, the sum of DDTs y and the sum of 9 PBDEs, with values that could be causing some toxic effects in the area of the most anthropogenically influenced colony. The estimated isotopic niche was also calculated, based on δ15N and δ13C, for the two colonies, pointing to a wider diet in the Cíes colony when compared to the diet in the Vigo colony. The study supports the use of the yellow-legged seagull eggs as a bioindicator of pollution capable of differentiating pollution level even in geographically close areas.

Seabirds and seals as drivers of plant succession on Surtsey

Plant colonization and succession on Surtsey have been monitored since 1965. In 2019, the 75th species of vascular plants was detected on the island, 62 species were present and about 40 species had established viable populations. Over the last decade colonization has slowed down and the number of present species not increased. The rising number of seagulls breeding on the island after 1985 had a great impact on plant colonization and vegetation development. While most parts of the island remained barren, a grassland area (13 ha in 2018) developed in the main seagull breeding colony on the southern part of the island. This development is attributed to transfer of nutrients from sea to land by the seagulls. In recent years a dense patch of vegetation, 2 ha in 2018, has also developed on the low, northern spit of the island, where a few pairs of seagulls breed in the spring and grey seals haul out and breed in the fall in considerable numbers. In a survey conducted during the grey seal pupping period in 2019, the seal abundance and spatial distribution was mapped accurately for the first time. The results show that the dense vegetation of the spit and seal distribution are clearly overlapping. The continuous shrinking of the island and its spit has led to an increasing concentration of the seals in their breeding area. Based on a literature survey we estimated the nitrogen (N) input from sea to land by the grey seals as 9-13 kg N/ha in 2019. This compares to an estimated input of 5-30 kg N/ha/yr by the seagulls breeding in the same area during 2015-2019. Within the grey seal and seagull breeding area on the spit of the island, a distinct community of shore plants has developed. Measurements of plant cover and biomass in permanent plots on Surtsey in 2018 and 2019 show that development on part of the spit is reaching a similar state as in the old gull colony on the southern part of the island. This suggests that the grey seals along with the seagulls are important drivers of plant succession on the northern spit. Further research on the effects of the seals on nutrient transfer from sea to land and ecosystem development on Surtsey is recommended.

Short report on probable case of Caspian Gull predation on migrating swallows observed at first time

AbstractAt Mietków Reservoir (SW Poland), during the breeding season of 2019, we found 52 dead swallows in Caspian Gull(Larus cachinnans)colony. Most of them were Barn Swallows(Hirundo rustica). The bodies of swallows were fresh and torn with traces of bill. We assume that swallows might have been in weak condition and hunted by gulls. They also could die because of bad weather conditions and hypothermia, fell into the water and then were taken. However, to our knowledge, it was the first mass event of feeding on migrating birds by Caspian Gull.

Stable isotopes reveal year-round sexual trophic segregation in four yellow-legged gull colonies

Sexual segregation in trophic ecology is widespread among sexually dimorphic marine vertebrates. The degree of such segregation can change throughout the annual cycle, however, year-round data on seabird inter-sexual differences are scarce. Here, we investigated sexual trophic segregation in yellow-legged gulls Larus michahellis evaluating two hypothetical drivers of such segregation: the different nutritional requirements hypothesis and the sexual size dimorphism hypothesis. We used stable isotope analyses of blood and feathers to estimate year-round gull trophic ecology in four colonies along the western Iberian coast. δ15N and δ13C values were consistently higher in males than in females throughout the year and in all four study colonies, suggesting consistent sexual differences in trophic level prey as well as in foraging habitats. Significantly wider isotopic niches of females in the innermost primary and eight secondary feathers suggest that they are more generalists than males during most of the annual cycle. In accordance, isotopic mixing models estimated a higher proportion of marine invertebrates in female diet, while males consumed a higher proportion of fish, which could indicate that males foraged more in association with fisheries, having major implications in view of the newly implemented discard ban policy. Overall, our results revealed a clear pattern of sexual trophic segregation in yellow-legged gulls that was maintained throughout the year in four colonies along the western Iberian coast, arguing against the different nutritional requirements hypothesis and suggesting that sexual size dimorphism plays an important role in driving sexual segregation in trophic niches.

Tetrabromobisphenol-A-Bis(dibromopropyl ether) Flame Retardant in Eggs, Regurgitates, and Feces of Herring Gulls from Multiple North American Great Lakes Locations.

The occurrence of tetrabromobisphenol-A-bis(2,3,-dibromopropyl ether) (TBBPA-BDBPE) flame retardant is generally unknown in wildlife. A highly sensitive, gas chromatography-mass spectrometry-based method was developed for TBBPA-BDBPE with optimized parameters for large volume injection. We report on TBBPA-BDBPE and temporal and spatial trends in herring gull egg pools and individuals from 14 colony sites across the Laurentian Great Lakes of North America. TBBPA-BDBPE identification was confirmed using liquid chromatography time-of-flight mass spectrometry and quantification with liquid chromatography tandem mass spectrometry analysis. TBBPA-BDBPE was quantifiable in 95% of egg pools from all colonies sampled in 2013-2017, and retrospective analysis of archived eggs (2001-2017) at 3 of the 14 colonies indicated that TBBPA-BDBPE concentrations were greater in pools from eggs collected in more recent years (<MLOD to 42.8 ng/g wet weight (ww)). For individual eggs, the concentration range was <MLOD to 497 ng/g ww. Individual eggs from 2 other herring gull colonies, north and south Pukaskwa National Park, Lake Superior, were analyzed for TBBPA-BDBPE, and dietary markers (fatty acids) revealed possible exposure pathways. Selected colonies with known dietary differences (i.e., terrestrial versus aquatic) indicated that TBBPA-BDBPE exposure was associated with terrestrial origin. Herring gull regurgitates and feces were collected from several colonies with TBBPA-BDBPE ranging from <MLOD to 21.7 ng/g dry weight (dw) and <MLOD to 16.3 ng/g ww, respectively. Typical of many alternate flame retardants in wildlife, TBBPA-BDBPE levels in the gull samples were low with a few high values and increasing prevalence through time.

Multiple factors associated with nest-site selection in a wetland-specialist, the Wren-like Rushbird (Phleocryptes melanops)

ABSTRACTDiverse factors may limit nest-site selection; however, nest predation has long been considered a main factor driving nest-site selection in birds. Marsh-nesting birds face a particularly important trade-off between habitat features that impede their vision of the approach of potential predators and nest concealment from predators. Here, we analyse how different ecological variables influence nest-site selection in the habitat-specialist Wren-like Rushbird (Phleocryptes melanops) breeding in three different wetlands of the Pampas region of Argentina over 3 years. Rushbirds selected nest sites with higher heights and denser vegetation, compared to random sites. Nest height was positively associated with vegetation height and lower visibility from the point of view of aerial predators, and the nest entrance was oriented towards the region with greatest visibility of the nest from the point of view of Rushbirds. Rushbirds seem to flexibly adjust their nest location in response to high predation risk, building their nests under structures built by other birds when breeding colonies of herons and gulls (potential nest predators) are present. Initial nest-site selection is performed by males, which then attempt to attract females to a rudimentary nest. Females sometimes reject such sites and the male then selects a new nesting location. Our study highlights the potential for flexible sex differences in nest-site selection.

Predator-prey dynamics of bald eagles and glaucous-winged gulls at Protection Island, Washington, USA.

Bald eagle (Haliaeetus leucocephalus) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous‐winged gull (Larus glaucescens) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers.To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka–Volterra‐type predator–prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other.The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics.Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction.Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator–prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

Great Crested Grebe (Podiceps cristatus) synchronies egg laying with protective species

Great crested grebes (Podiceps cristatus) are opportunistic breeders nesting in colonies or solitarily in different biotopes with varying nesting dates in different circumstances. On the northern coast of the Neva Bay in the eastern part of the Gulf of Finland, great crested grebes breed solitarily, in colonies situated in reed beds and in a colony on the open water in direct vicinity of a colony of black-headed gulls (Larus ridibundus) and black terns (Chlidonias niger). In the vicinity of the larid colony, grebes profit from the protecting behaviour of gulls and terns in a similar way as they do in their mixed colonies with larids. Despite the fact that small larids have a shorter incubation period than great crested grebes, the latter synchronize their beginning of incubation with the gulls and terns. The incubation of all three species in two adjoining open-water colonies started on the same dates. The incubation of grebes nesting in the reed beds began significantly later. The average clutch sizes did not differ significantly between the colonies situated on the open water near larids and those in the reeds. The average lowest distances between the nests of great crested grebes in the open water colony were larger than in the reed bed colonies. The ability to synchronize the beginning of incubation with a small protecting species helps great crested grebes to occupy otherwise unsafe habitats.

Does the vicinity of the Black-Headed Gull colony (Chroicocephalus ridibundus) increase the breeding success of the Common Tern (Sterna hirundo) on the islands of the middle Vistula?

We conducted our study in the Common Tern colony (STH) located on an island in the middle Vistula River course, at the height of the city of Dęblin (km 393–394 of the waterway), in 2017. Our goal was to investigate some aspects of the biology and reproductive ecology of this species. Due to the fact that STH breeds both in single-species as well as in two- or multi-species colonies, in associations with Little Terns (Sternula albifrons), Black-Headed Gulls (Chroicocephalus ridibundus) (LAR) and/or Mew Gulls (Larus canus), we wanted to investigate whether the neighborhood of other species (in this case LAR) affected hatching success and chick survival in STH. Our results clearly show that the presence of breeding terns in the neighborhood of the LAR colony was not accidental and/or caused by the lack of space on the island and/or the possibility of nesting elsewhere. The height of nesting site, type of nesting habitat, clutch size, mean egg volume and mean egg mass of these STH pairs did not differ significantly from those that formed a single species colony, on the same island but several hundred meters away. However, STH nests in the neighborhood of the LAR colony were established much earlier and both the hatching success and chick survival of STH during the early-chick stage were twice as high. Thus, we can conclude that the LAR colony could provide an effective protection against predation of crows, magpies and gulls, dangers which accounted for the vast majority of STH nest failures in the year of our study.

Collapse of a protector species drives secondary endangerment in waterbird communities

Interactions and dependence between species can transmit the effects of species declines within and between trophic levels, resulting in secondary endangerments and, in some cases, extinctions. Many mixed-species avian breeding aggregations commonly have a protector species whose aggressive nest defense is used by other species to defend their nests. Disappearance of the protector species may have population demographic consequences on the dependent species. Aggressive nest defense behavior of small colonial gulls, such as the black-headed gull (Chroicocephalus ridibundus), is used by many waterbird species to gain protection against predators. We used data from 15 local waterbird communities in Finland to study long-term changes and dynamics of breeding numbers of other waterbirds as a response to long-term changes and dynamics of black-headed gull colonies. We found that breeding numbers of many species tracked long-term changes in the size of black-headed gull colonies. This was true even after controlling for a common trend in the size of the black-headed gull colony and the breeding numbers of the other species. The trend-controlled positive temporal association with black-headed gull was relatively stronger in species that nest in similar habitats of a lake as the black-headed gull, and in species that have a more critical conservation status due to drastic population decline. Our results suggest that the overall decline of black-headed gull colonies has resulted in secondary endangerment of many other species in waterbird communities.

Can drones count gulls? Minimal disturbance and semiautomated image processing with an unmanned aerial vehicle for colony-nesting seabirds.

Accurate counts of wild populations are essential to monitor change through time, but some techniques demand specialist surveyors and may result in unacceptable disturbance or inaccurate counts. Recent technological developments in unmanned aerial vehicles (UAVs) offer great potential for a range of survey and monitoring approaches. They literally offer a bird's‐eye view, but this increased power of observation presents the challenge of translating large amounts of imagery into accurate survey data. Seabirds, in particular, present the particular challenges of nesting in large, often inaccessible colonies that are difficult to view for ground observers, which are commonly susceptible to disturbance. We develop a protocol for carrying out UAV surveys of a breeding seabird colony (Lesser Black‐backed Gulls, Larus fuscus) and subsequent image processing to provide a semiautomated classification for counting the number of birds. Behavioral analysis of the gull colonies demonstrated that minimal disturbance occurred during UAV survey flights at an altitude of 15 m above ground level, which provided high‐resolution imagery for analysis. A protocol of best practice was developed using the expertise from both a UAV perspective and that of a dedicated observer. A GIS‐based semiautomated classification process successfully counted the gulls, with a mean agreement of 98% and a correlation of 99% with manual counts of imagery. We also propose a method to differentiate between the different gull species captured by our survey. Our UAV survey and analysis approach provide accurate counts (when comparing manual vs. semi‐automated counts taken from the UAV imagery) of a wild seabird population with minimal disturbance, with the potential to expand this to include species differentiation. The continued development of analytical and survey tools whilst minimizing the disturbance to wild populations is both key to unlocking the future of the rapid advances in UAV technology for ecological survey.