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Storm-induced shifts in optimal nesting sites: A potential effect of climate change

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Extreme storm events encountered during any stage of the annual cycle can result in increased mortality and influence population dynamics. Storms during the reproductive season, when birds are tied to fixed nesting locations, can be particularly problematic. Given predicted changes in the frequency and intensity of storms in a changing climate, studies examining the impacts of storms on reproductive success in model systems are important. Island-nesting seabirds may be particularly vulnerable to changes in storm frequency and intensity. Here, we report on the effects of an extreme storm in June 2012 on Herring Gull (Larus argentatus) reproduction on an island in the Gulf of Maine, USA. More than 22 % of monitored nests were lost in this single event leading to a seasonal shift in the optimal nesting locations for birds in our population. Nests closer to water and nests located at low elevations were disproportionately affected by the unusual weather, reversing trends in optimal nesting sites recorded in previous seasons. Spatiotemporal shifts in optimal nesting locations, therefore, may be one result of climate-induced changes in storm frequency and intensity. Although some birds with nests destroyed in the storm attempted to renest, these attempts experienced low success, and overall reproductive success in the storm-affected season was lower than in the previous three nesting seasons.
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... Interior or Exterior -Lower success at exterior nests due to exposure to storms and flooding (Sherley et al. 2011;Bonter et al. 2014). ...
... Distance to water had a weak negative effect on DSR during incubation in 2018. Many studies of seabirds nesting on islands have found that proximity to water decreased reproductive success and recruitment, as wave activity, precipitation, and flooding from storm events increased This study the mortalities in nests closer to water sources (Sherley et al. 2011;Walter et al. 2013;Bonter et al. 2014). However, most Brown Pelican nests on Gaillard Island occur between the armored island perimeter and the berm, and thus appear to be relatively protected from over-wash events. ...
... activity and flooding decrease reproductive success of low-lying nests(Sherley et al. 2011;Walter et al. 2013;Bonter et al. 2014). ...
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In the northern Gulf of Mexico, island restoration and creation have been used to mitigate potential negative effects of anthropogenic and environmental stressors to breeding seabirds. The long-term success of such projects can be enhanced when data are available to elucidate how site-specific and larger-scale factors may contribute to reproductive success. Nest-specific daily survival rate (DSR) of Eastern Brown Pelicans (Pelecanus occidentalis carolinensis) during incubation (i.e., pre-hatch; n = 245) and brood-rearing (i.e., post-hatch; n = 185) were measured at two breeding islands in the northern Gulf of Mexico USA in 2017 and 2018 in relation to macro- and micro- scale habitat and environmental measurements. DSR of nests during incubation ranged from 91-99%, and the DSR during brood-rearing exceeded 99% each year. Regional weather variables occurred in top-performing models more often and with more significance compared to microhabitat variables. Results suggest that reproductive success of Brown Pelicans may respond at least in part to weather factors that occur outside of the scope of habitat structure as it is typically incorporated into the restoration or creation of breeding habitat, indicating that climate conditions are likely an important factor in the success of restoration efforts.
... Because the frequency of storms is expected to increase, investigations looking at the effect of severe storms on avian species and important habitats, such as wetlands, is crucial. Extreme disturbance events, such as storms, can affect avian nesting success and lead to shifts in optimal nesting locations (Bonter et al. 2014), which can have implications for avian reproductive and population success and landscape-level habitat use. ...
Article
Wetlands provide numerous ecosystem functions such as water purification, nutrient cycling, and wildlife habitat. Avian populations are indicators of wetland health, and understanding their responses to extreme events can aid in targeting restoration efforts following disturbance. Here, we assessed the habitat selection of six coastal wetland bird species (American Bittern, Black-crowned Night Heron, Great Egret, Glossy Ibis, Snowy Egret, Yellow-crowned Night Heron) related to an extreme weather event, Hurricane Sandy. We used Discrete Choice Resource Selection Functions to estimate habitat selection. Results showed species probability of use increased with lower elevation and slope, and closer proximity to marsh, salt marsh, Phragmites, and protected areas. Estimates of marsh dieback from Hurricane Sandy occurred disproportionately in areas with higher probability of species use. Species were observed farther from the coast and at higher elevations in the four breeding seasons after (2013–2016) compared to before (2000–2012) Hurricane Sandy. Our results indicate that although high suitability areas were affected by the storm, these six wetland bird species may have responded by moving inland and to higher elevation. Understanding how coastal wetland birds respond to storm events is important for conservation planning, particularly as storm frequency is projected to increase in the future.
... However, more substantial analyses are needed to ascertain which components of the wind field are most important when it comes to site selection. Even then, it may be difficult to disentangle the ultimate drivers of site selection, as shelter from strong winds could also be important in reducing exposure to low temperatures, or the possibility of young being swept off ledges by strong winds or associated wave action (Bonter et al., 2014;Høyvik Hilde et al., 2016). Furthermore, shelter is likely to improve the ability of fledglings to jump and reach the sea at the end of the season (Gilchrist and Gaston, 1997). ...
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For fast-flying birds, the ability to respond to wind during landing is critical, as errors can lead to injury or even death. Nonetheless, landing ability, and its ecological significance, remain unstudied. We show that for auks, 60% of attempts to land at their cliff nests fail in a strong breeze (80% in near-gale winds). This is most likely because wind interferes with the ability to maintain flight control in the last phase of landing. Their extreme flight costs mean that the energetic penalty for multiple landing attempts is high. We propose that exposure, and ability to respond to, such conditions will influence the suitability of breeding habitat. In support of this (i) auk colonies appear to be orientated away from prevailing winds and (ii) landing success within colonies is higher on crowded ledges with more airspace for manoeuvring. More generally, the interplay between wind and flight capacities could impact breeding distributions across species and scales.
... Sea-level rise will reduce the availability of habitat for intertidal species (Galbraith et al. 2002), particularly where human development prevents natural migration of coastal habitats inland. Projected increases in the severity and frequency of weather events, such as storms, are likely to cause increased damage to seabird breeding sites and increase chick mortality (Croxall et al. 2012;Bonter et al. 2014), and sea-level rise is expected to worsen such impacts (Van De Pol et al. 2010 to climate change is considered a threat to species in Red List assessments. ...
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en International Union for Conservation of Nature (IUCN) Red List assessments rely on published data and expert inputs, and biases can be introduced where underlying definitions and concepts are ambiguous. Consideration of climate change threat is no exception, and recently numerous approaches to assessing the threat of climate change to species have been developed. We explored IUCN Red List assessments of amphibians and birds to determine whether species listed as threatened by climate change display distinct patterns in terms of habitat occupied and additional nonclimatic threats faced. We compared IUCN Red List data with a published data set of species’ biological and ecological traits believed to infer high vulnerability to climate change and determined whether distributions of climate change‐threatened species on the IUCN Red List concur with those of climate change‐threatened species identified with the trait‐based approach and whether species possessing these traits are more likely to have climate change listed as a threat on the IUCN Red List. Species in some ecosystems (e.g., grassland, shrubland) and subject to particular threats (e.g., invasive species) were more likely to have climate change as a listed threat. Geographical patterns of climate change‐threatened amphibians and birds on the IUCN Red List were incongruent with patterns of global species richness and patterns identified using trait‐based approaches. Certain traits were linked to increases or decreases in the likelihood of a species being threatened by climate change. Broad temperature tolerance of a species was consistently related to an increased likelihood of climate change threat, indicating counterintuitive relationships in IUCN assessments. To improve the robustness of species assessments of the vulnerability or extinction risk associated with climate change, we suggest IUCN adopt a more cohesive approach whereby specific traits highlighted by our results are considered in Red List assessments. To achieve this and to strengthen the climate change‐vulnerability assessments approach, it is necessary to identify and implement logical avenues for further research into traits that make species vulnerable to climate change (including population‐level threats). Abstract es Los Patrones y Sesgos de las Amenazas del Cambio Climático en la Lista Roja de la *IUCN Resumen Las evaluaciones de la Lista Roja de la Unión Internacional para la Conservación de la Naturaleza (IUCN) dependen de datos publicados contribuciones de expertos, y los sesgos pueden introducirse en donde los conceptos y definiciones subyacentes son ambiguos. La consideración de la amenaza del cambio climático no es una excepción, y recientemente se han desarrollado numerosas estrategias para evaluar esta amenaza hacia las especies. Exploramos las evaluaciones de la Lista Roja de la IUCN de anfibios y aves para determinar si las especies enlistadas como amenazadas por el cambio climático muestran patrones marcados en términos del hábitat ocupado y las amenazas no‐climáticas adicionales que enfrentan. Comparamos los datos de la Lista Roja de la IUCN con un conjunto de datos publicados sobre las características biológicas y ecológicas de las especies que se creen infieren una alta vulnerabilidad ante el cambio climático y determinamos si la distribución de las especies amenazadas por el cambio climático en la Lista Roja coincide con aquellas especies amenazadas por el cambio climático identificadas con la estrategia basada en las características y si las especies que poseen estos rasgos tienen mayor probabilidad de tener al cambio climático enlistado como una amenaza en la Lista Roja. Las especies de algunos ecosistemas (p. ej.: pastizal, matorral) y sujetas a amenazas particulares (p. ej.: especies invasoras) tuvieron mayor probabilidad de tener al cambio climático enlistado como amenaza. Los patrones geográficos de los anfibios y aves amenazados por el cambio climático en la Lista Roja fueron incongruentes con los patrones de la riqueza global de especies y los patrones identificados con el uso de estrategias basadas en las características. Ciertas características estuvieron relacionadas con los incrementos y disminuciones en la probabilidad de que una especie estuviera amenazada por el cambio climático. La tolerancia térmica general de las especies estuvo relacionada constantemente con una mayor probabilidad de amenaza por el cambio climático, lo que indica relaciones contradictorias en las evaluaciones de la IUCN. Para mejorar la robustez de las evaluaciones de la vulnerabilidad o el riesgo de extinción de las especies asociados con el cambio climático, sugerimos que la IUCN adopte una estrategia más cohesiva en la que las características específicas resaltadas por nuestros resultados sean consideradas en las evaluaciones de lista roja. Para obtener esto y para fortalecer la estrategia de evaluaciones de vulnerabilidad por cambio climático, es necesario identificar e implementar vías lógicas para las futuras investigaciones sobre los caracteres que hacen que las especies sean vulnerables al cambio climático (incluyendo amenazas a nivel poblacional).
... However, SLR combined with climate change may affect not only regular tidal cycles, but also the frequency and severity of storms (Bender et al. 2010). Storms have been shown to affect not only nesting success, but also nest-site selection behaviors (Bonter et al. 2014). Because storms may come at any point during a tidal cycle, they may affect Seaside Sparrow nesting success similarly to predation by disrupting the synchronization between nest initiation and cycles of lunar tides. ...
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Sea-level rise (SLR) threatens the nesting success of salt marsh breeding birds, including Seaside Sparrows (Ammodramus maritimus), by increasing the magnitude and frequency of extreme high tides that flood nests. However, the threat to nesting success from tidal flooding is intertwined with that of predation because the threats are connected through a trade-off along a nest height gradient. Therefore, to understand the risk to nesting success from SLR, it is necessary to consider predation threats simultaneously. I used an individual-based model of Seaside Sparrow nesting behavior, calibrated using empirical data on nest success rates and nest-site selection behaviors, to project the effects of SLR conditions on the relative importance of predation and flooding threats in affecting nesting success, and to investigate whether nest-site selection along a gradient of nest height can modulate the risk of SLR. Outputs from the model revealed that present-day levels of predation risk pose as great a risk to nesting success as tidal flooding under simulated SLR conditions with extreme flooding risks. Nest success rates could become very low under extreme SLR scenarios, especially when predation risk is very high. The risks of failure from either threat are linked through nest- site selection behaviors: In high-predation-risk seasons, failure probability from flooding is greater than it would be under lower predation risk, due to the predation avoidance behavior of nesting closer to the ground. Therefore, management actions to reduce the risk of excessive failures from predation could reduce the risk of failures from both threats—a potentially useful management strategy, given that controlling predation is more tractable than controlling increased flooding from SLR at a local level.
... The southern Great Plains in particular will become more arid, with increased frequency of extreme heat events and fewer precipitation events (Karl et al. 2009). When precipitation comes in the form of strong storms, wind, hail, and heavy rain can destroy nests and their contents (Martínez et al. 2013, Bonter et al. 2014. Nest thermal ecology and resultant egg and nestling survival are likely to be affected by climate change, but are generally poorly described (Grisham et al. 2016). ...
Article
Identifying sources of annual variation in the reproductive success of a species may provide valuable insights into how the species may be affected by future environmental or climatic conditions. We examined annual variation in the nesting phenology, productivity, and apparent nest success of Mississippi Kites (Ictinia mississippiensis), a species common in urban areas in the southern Great Plains, from May through August. We monitored 498 Mississippi Kite nesting attempts in Lubbock, Texas, USA, between 2004 and 2015, from which we modeled daily survival rate as a function of local weather conditions, drought severity, and the state of the El Niño Southern Oscillation. We observed significant annual variation in median incubation initiation date (range = May 20 to June 5), the probability of nest success (range = 0.31-0.90), and productivity (range = 0.25-1.00 fledglings per nest). Our models of daily survival rate suggested that higher daily temperatures, severe storm events, extreme drought conditions, and La Niña events negatively influenced nest survival. These results suggest that increasing storm frequency and higher temperatures associated with climate change are likely to decrease the nesting success of Mississippi Kites in the southern Great Plains.
... We might expect, therefore, that body condition at hatching will determine offspring survival probability during the nestling period. In addition, weather conditions during the breeding period can also have an impact on offspring survival (Bradley et al. 1997, Ouyang et al. 2015, for example, strong storms can cause high rates of chick mortality (Bonter et al. 2014). In this context we predict that precipitation and low temperatures could decrease the probability of survival. ...
Article
Capsule: Pre-fledging survival in a Yellow-legged Gull Larus michahellis population in northern Iberia is negatively correlated to hatching date. Aims: To explore which factors have more importance in determining the pre-fledging daily survival rates in a Yellow-legged Gull population from northern Iberia. Specifically, we tested for the effect of hatching date and order, body size and condition and meteorological conditions on pre-fledging survival. Methods: Cormack–Jolly–Seber models with mixtures were used to model daily survival rates. Results: Daily survival rates were mostly negatively affected by hatching date. Conclusions: Hatching date was the most important factor affecting survival of chicks during the pre-fledging period in a Yellow-legged Gull colony from northern Iberia.
... Avian nests are susceptible to a wide range of environmental factors that can affect breeding behaviors and nest success (Ricklefs 1969, Dunning and Watts 1991, Penteriani et al. 2002, Bonter et al. 2014. In species that construct nests in trees or on cliffs, extreme weather and nest age can compromise the integrity of the nest, causing complete or partial nest collapse (Grieco 1999, Martínez et al. 2013. ...
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Nest collapse has been documented in many bird species, with little discussion of adult behavior following collapse. We present evidence of a partial collapse of a Gyrfalcon (Falco rusticolus) nest during the nestling period and the subsequent adult response. A nest camera captured the nest collapse and showed one adult Gyrfalcon holding a live nestling in its beak before leaving the nest. Later, we found the surviving nestling alive in an alternate nest 5 m from the original nest, presumably transported there by the adult. We believe this is the first report of an adult Gyrfalcon moving a nestling to a new location following nest disturbance. We place this observation into a context of Gyrfalcon nesting behavior described in published sources. The continued use of nest cameras may provide additional documentation and insight into this behavior and its prevalence in birds.
... This study has shown that wind speed may be a critical factor that can lead to low breeding success in birds in temperate latitudes, and not just in low latitudes (James and Wunderle 1993) or on sea coasts (e.g. van de Pol et al. 2010;Bonter et al. 2014). Another important result is that CHL, which begins breeding on average 8 days later than CHN, had a much lower hatching success. ...
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Identifying the key factors governing the expansion of a species’ range is difficult because of the multiple interactions of environmental and biological factors. Among the biological factors are breeding parameters, which at the edge of a species’ range may indicate the traits involved in limiting species distribution. To evaluate whether the hatching success of two sympatric species of terns was dependent on weather parameters, a study was carried out in the valley of the River Bug in eastern Poland. During 2007–2010, nine colonies with 113 clutches of White-winged Tern (CHL, an expansive species, new to the region since 1997) and 92 clutches of Black Tern (CHN, a non-expansive species, nesting in stable numbers in this region for many years) were monitored. CHN arrived on average 9 days earlier than CHL. While CHN arrived in east-central Poland earlier and earlier during the 1998–2013 period, no such trend was recorded for CHL. The clutch initiation median in CHL was 8 days later than in CHN. The hatching success of CHL was statistically less than that of CHN (41.6 vs. 69.6%). A general discriminant analysis model showed that successful CHL clutches depended on the maximum daytime wind speed (strong winds can be disastrous for breeding terns), colony identity and clutch initiation date. In the case of CHN, none of these factors had a statistically significant influence on hatching success, although the clutch initiation date was very close to being significant. These results suggest that a species which nested in the same location for a long time in relation to ambient weather conditions has higher hatching success than the one which is in the process of expanding its distribution range.
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For ground- and burrow-nesting birds, heavy rain events can lead to reproductive failure when nests flood. This paper describes the exposure of Florida Burrowing Owls (Athene cunicularia floridana) to breeding season flooding, its relationship to annual reproductive success rates, and effect on nest failure across 5 cattle ranches in southwestern Florida, USA. In May 2016, a heavy rain event following an unusually wet dry season led to extensive burrow flooding and widespread reproductive failure in 1 of the breeding sites under study. In 2017 and 2018, burrows flooded frequently but the occurrence of flooding later in the breeding season was not associated with a lower overall annual reproductive success rate. Brood age at the time of flooding had a significant relationship with the probability that a particular nest failed, with the chance of event survival increasing from 12% in week 3 to 58% in week 4. All but 1 brood that experienced flooding in week 5 or later survived at least partially. Our findings indicate that flooding is a common occurrence that Florida Burrowing Owls breeding on cattle ranches can tolerate, but extreme precipitation, especially early in the breeding season or when broods are young, can cause widespread nest failure. Annual productivity could be affected if these events increase in frequency with climate change, but the inclusion or maintenance of elevated ground within the ranch landscape could provide refugia. Para aves que anidan en el suelo o en cuevas en el suelo, los eventos de fuertes lluvias pueden conducir a fallos reproductivos cuando los nidos se inundan. Este artculo describe la exposicin de los bhos Athene cunicularia floridana a inundaciones durante la poca reproductiva, su relacin con tasas anuales de xito reproductivo y efectos en el fallo de nidos en 5 ranchos ganaderos en el suroeste de Florida, EUA. En mayo de 2016, un evento de fuertes lluvias despus de una estacin de secas inusualmente hmeda tuvo como consecuencia extensas inundaciones de cuevas en el suelo y amplios fallos reproductivos en 1 de los sitios reproductivos de este estudio. En 2017 y 2018, las cuevas en el suelo se inundaron frecuentemente, aunque la incidencia de inundaciones en la estacin reproductiva avanzada no estuvo asociada en lo general con una menor tasa reproductiva anual. La edad de la nidada al momento de la inundacin tuvo una relacin significativa con la probabilidad de que un nido en particular fallara, con incrementos en la probabilidad de sobrevivencia a estos eventos de 12% en la semana 3 a 58% en la semana 4. Con excepcin de una nidada, todas las que experimentaron inundaciones en la semana 5 o posterior sobrevivieron al menos parcialmente. Nuestros hallazgos indican que las inundaciones ocurren frecuentemente y que los bhos que anidan en estos ranchos ganaderos los pueden tolerar, aunque las precipitaciones extremas, especialmente en la parte temprana de la temporada reproductiva o cuando las nidadas son jvenes, pueden causar fallos de nidos ampliamente distribuidos. La productividad anual podra ser afectada si estos eventos se incrementan en frecuencia con el cambio climtico, si bien la inclusin o mantenimiento de terrenos elevados en el paisaje del rancho podran proporcionar refugios. Palabras clave: anidacin en el suelo, llanuras, mortandad de nidos, praderas, precipitacin extrema.
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The Bermuda Petrel Pterodroma cahow was thought to have become extinct early in the 17th century due to a combination of hunting by human colonists and predation by introduced rats, cats, dogs and pigs. However, single individuals were found on four occasions during the first half of the 20th century, and in 1951 a small population was discovered breeding on several rocky islets in north-east Bermuda. Recovery actions began in 1962 when the population numbered just 18 pairs, dispersed among five small islets. Although rats extirpated one of these five colonies in 1967, the population has grown steadily to 56 breeding pairs in 2000. We investigated the breeding phenology, productivity and population size of the Bermuda Petrel between 2000/2001 and 2007/2008. Each year, the birds began arriving in Bermuda around mid-October. They departed on a pre-breeding exodus between 19 November and 14 December, returning after 32–56 days to lay a single egg between 31 December and 31 January. Eggs hatched from 16 February to 26 March after a mean (± SD) incubation period of 53 ± 2 days, and young fledged from 15 May to 25 June after a mean fledging period of 91 ± 5 days. Between 2000/2001 and 2007/2008, reproductive output ranged from 29 to 40 fledglings per annum. Mean annual breeding success (62%) was reasonably high relative to other Procellariiformes, largely due to the provision of artificial (concrete) nesting burrows. In 2008, the population numbered 85 breeding pairs. Monitoring since 1961 indicates the population has been increasing exponentially, doubling approximately every 22 years. This rate of increase, together with the increased incidence of storm damage, is making it progressively more impracticable to construct sufficient concrete burrows on the current nesting islets to accommodate all breeding pairs. The vulnerability of these sites to accelerating storm damage and erosion as a result of anthropomorphic climate change is now the greatest threat to the Bermuda Petrel.
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We developed a Markov process model for colony-site dynamics of Gull-billed Terns (Sterna nilotica). From 1993 through 1996, we monitored breeding numbers of Gullbilled Terns and their frequent colony associates. Common Terns (Sterna hirundo) and Black Skimmers (Rynchops niger), at colony sites along 80 km of the barrier island region of coastal Virginia. We also monitored flooding events and renesting. We developed the model for colony survival, extinction, and recolonization at potential colony sites over the four-year period. We then used data on annual site occupation by Gull-billed Terns to estimate model parameters and tested for differences between nesting substrates (barrier island vs. shellpile). Results revealed a dynamic system but provided no evidence that the dynamics were Markovian, i.e. the probability that a site was occupied in one year was not influenced by whether it had been occupied in the previous year. Nor did colony-level reproductive success the previous season seem to affect the probability of site occupancy. Site survival and recolonization rates were similar, and the estimated overall annual probability of a site being occupied was 0.59. Of the 25 sites that were used during the four-year period, 16 were used in one or two years only, and only three were used in all four years. Flooding and renesting were frequent in both habitat types in all years. The frequent flooding of nests on shell-piles argues for more effective management; augmentation with shell and sand to increase elevations as little as 20 cm could have reduced flooding at a number of sites. The low colony-site fidelity that we observed suggests that an effective management approach would be to provide a large number of sand and / or shellpile sites for use by nesting terns. Sites not used in one year may still be used in subsequent years.
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This study examined nest site selection within Eared Grebe (Podiceps nigricollis) colonies in terms of nesting synchrony, nearest-neighbor distances, vegetation, exposure, and nest success. Nests in 11 Eared Grebe colonies in Minnesota were initiated over a span of 11-45 days, with most nests in each colony initiated in < 11 days. In each of six colonies studied, mean nearest-neighbor distance of the earliest nests was greater than that of the complete colony. Nearest-neighbor distance tended to decrease with an increase in emergent vegetation density. Early nests seemed to form the skeleton of a neighborhood, with later nests filling in or establishing other neighborhoods. In five of six colonies, clutch sizes were larger in earlier nests. No significant difference in egg volume between early and late nests was apparent in the two colonies studied. Early nests were more successful than were late nests in two of four colonies; center nests were more successful than were edge nests at only one of four colonies. Most nest destruction in this study was caused by waves generated by high winds; <2% of nests showed evidence of predation.
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From 1986 to 1988 the breeding biology of an endangered Hawaiian honeycreeper, the Laysan Finch (Telespiza cantans), was studied on the coral island of Laysan in the Hawaiian Archipelago. Laysan Finches are apparently monopmous. Pairs defend mates and nest sites, but not feeding territories. Only the female constructs the nest and incubates. The breeding season is prolonged, but there is yearly variation in onset. Pairs can have more than one clutch per year. The average clutch size was 3.19 eggs. The modal incubation period was 16 days. One-third of all eggs laid disappeared, probably due primarily to intraspecific predation. Eggs hatched asynchronously in the order laid. Chicks fledged at 22-26 days of age, and were dependent for at least three additional weeks. Weather affected reproductive success. A severe storm in 1986 caused almost total mortality of eggs and chicks, regardless of clutch size. Later in that same year, fledglings per nest increased as clutch size increased. During the dry 1987 field season, the onset of breeding was delayed, mean egg weight decreased, the number of malformed eggs increased, and clutches tended to be smaller. Although in good years four-egg clutches produced more fledglings per nest than smaller clutches, in poorer years three-egg clutches produced at least as many or more fledglings per nest than larger clutches. In this fluctuating environment, a modal clutch size of three apparently has been selected for, possibly because it yields the highest average number of offspring per nest during both good and poor years.
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We present a method for making direct quantitative measurements of population dymamics of fish species preyed upon by seabirds. We studied foraging behavior of Common Terns (Sterna hirundo) in relation to density of fish prey of Long Island, New York. We used an echo sounder to record the abundance of small prey fish and large predatory fish near a tern colony. Prey fish abundance was highest when terns were feeding young chicks and declined sharply later in the season, coincident with the arrival of large numbers of predatory bluefish (Pomatomus saltarix). Mean depth of occurrence of prey fish was shallower after the arrival of bluefish. Terns fished in areas with high concentrations of prey, but there was no correlation between numbers of feeding terns and prey density. Number of feeding terns was inversely correlated with prey depth, however. Terns were strongly attracted to predatory fishes feeding near the surface. We suggest that in addition to concentrating prey fish near the surface, predatory fish may have been important as competitors.
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From 1987-1989, I used ground measurements and aerial photography of marked colonies to describe and study the selection of 12 colony sites on nine Eared Grebe (Podiceps nigricollis) breeding wetlands in Minnesota. Colonies were located in moderately dense to sparse green or dead emergent vegetation or on surface mats of filamentous green algae or submerged aquatic macrophytes. All colony sites were near open water or channels and two were near larid colonies. Wave action generated by high winds destroyed seven of 15 colonies (44% of 2370 nests) marked or examined in this study. Nest predation, almost exclusively by American Coots (Fulica americana), was low (< 3% in any colony). Distance from shore (0.09 to 1.5 km) seemed a compromise between terrestrial predator pressure and higher waves associated with a deeper, less vegetated wetland center. Mean water depth at the colony sites ranged from 50 to 120 cm; one colony may have abandoned its nests when water depths became too shallow-while another colony site was in the deepest water available on a wetland during a drought year.
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When animals that provide parental care to offspring are faced with actual or potential failure during a breeding bout, the option to continue breeding is countered by the option to cut losses and forego reproduction until the next breeding season. In 1990, we recorded laying date and laying order of eggs in 51 Ring-billed Gull (Larus delawarensis) clutches prior to their total loss by flooding. Pairs remained on territory and produced new clutches following a refractory period of 11.6 ± SD of 1.9 days. Post-loss clutches were initiated synchronously (n = 51 clutches in four days; 89% of all clutches marked in the 7 × 7 m study plot) but mostly contained significantly fewer and lighter eggs than first clutches. We contrast incubation, hatching and chick survival patterns of these storm-delayed pairs in 1990 with patterns of early-, peak- and late-nesting pairs at the same colony in 1992. The incubation and within-clutch hatching patterns of post-loss clutches 1990 were most similar to those of late n