Bird Rookeries Research Articles

Bird rookery nutrient over-enrichment as a potential accelerant of mangrove cay decline in Belize.

Coastal eutrophication is an issue of serious global concern and although nutrient subsidies can enhance primary productivity of coastal wetlands, they can be detrimental to their long-term maintenance. By supplying nutrients to coastal ecosystems at levels comparable to intensive agriculture practices, roosting colonial waterbirds provide a natural experimental design to examine the impacts of anthropogenic nutrient enrichment in these systems. We tested the hypothesis that long-term nutrient enrichment from bird guano deposition is linked to declines in island size, which may subsequently decrease the stability and resilience of mangrove cays in Belize. We combined remote sensing analysis with field- and lab-based measurements of forest structure, sediment nutrients, and porewater nutrients on three pairs of rookery and control cays in northern, central, and southern Belize. Our results indicate that rookery cays are disappearing approximately 13 times faster than cays without seasonal or resident seabird populations. Rookery cays were associated with a significantly higher concentration of nitrogen (N) in mangrove leaves and greater aboveground biomass, suggesting that eutrophication from bird guano contributes to increased aboveground productivity. Sediments of rookery cays also had lower percentages of soil organic matter and total N and carbon (C) than control islands, which suggests that eutrophication accelerates organic matter decomposition resulting in lower total C stocks on rookery cays. Our results indicate that coastal eutrophication can reduce ecosystem stability by contributing to accelerated cay loss, with potential consequences for mangrove resilience to environmental variability under contemporary and future climatic scenarios.

An experimental test of crocodilian stick-displaying behavior

Tool use has been documented across a diverse array of animals; however, this behavior has received little attention in reptiles. Recently, researchers reported observations of two crocodilian species apparently using sticks as lures to aid in the capture of nesting birds, but the evidence for the behavior was anecdotal and correlative. To explore the behavior in a more controlled situation we designed an experiment to explicitly test the ability of crocodilians to tailor stick-displaying behaviors to specific environmental contexts using four captive pond-dwelling American alligator (Alligator mississippiensis) populations, two of which reside near bird rookeries and two of which do not. During bird nesting season we added sticks to each pond and observed the frequency with which each population exhibited stick-displaying behaviors. We found that in most comparisons the frequency of stick-displaying behavior did not differ between rookery and no-rookery sites, while in one comparison the alligators at a no-rookery site actually displayed the behavior more frequently than a paired rookery site. Our results do not generally support the hypothesis that crocodilians tailor stick-displaying behaviors to specific environmental contexts, therefore the hypothesis that crocodilians are true tool users is also called into question. Furthermore, our results suggest that experiments on captive populations are not the ideal way to study stick-displaying behavior because of issues like unrealistic alligator densities and food provisioning.

Collapse of a unique insular bird–snake relationship

AbstractSeahorse Key (SHK) supports a population of Florida cottonmouth snakes, Agkistrodon conanti, which have a unique trophic association with colonially nesting waterbirds. Each spring >10 000 birds have nested on SHK and provided an influx of food in the form of fish carrion that snakes scavenge on the ground. Because of this allochthonous input of trophic resources, the cottonmouth population on SHK historically was dense, with snakes of large body size. Suddenly and unexpectedly, the entire waterbird colony abandoned its nests during April, 2015 and did not return. We examined data collected from 1999 to 2016 on the abundance and body size of SHK cottonmouths to quantify how the bird abandonment has affected the snake population. Our results show that abundance and body condition index (BCI) have decreased significantly, particularly on the west end of SHK where the bird rookery historically concentrated. Abundance of snakes (counts per survey) along a west beach transect was higher during the pre‐abandonment period (10.99 ± 8.11 SD) than during the post‐abandonment period (7.52 ± 4.64). Similarly, we observed a significant decrease in the BCI of snakes from the west end of SHK between the pre‐ (0.04 ± 0.10) and post‐abandonment periods (−0.12 ± 0.14). Loss of the bird rookery as a source of energy has negatively affected the SHK cottonmouth population. In contrast, numbers and body condition of cottonmouths appear to have increased on an adjacent island where ~3000 to 5000 waterbirds began nesting in 2015 and 2016.

Cane toads beneath bird rookeries: utilization of a natural disturbance by an invasive species.

Many invasive species exploit anthropogenically disturbed habitats, but most of those taxa evolved long before humans. Presumably, then, an ability to use natural (non-anthropogenic) disturbances pre-adapted invaders to a world later degraded by people. Studies on invasive species in naturally disturbed habitats thus can clarify the ancestral niche of invaders. In the Australian tropics, metallic starlings Aplonis metallica nest communally in emergent rainforest trees during the wet-season, and invasive cane toads Rhinella marina join other predators (mammals, birds, reptiles, and other anurans) to exploit the food resources beneath those trees. Compared to conspecifics found along nearby roads through the forest, cane toads beneath bird-nesting trees occur at higher densities, and are smaller in body size. The sex ratio is female-biased, and recapture records suggest that females may be philopatric at these sites (whereas recaptures were rare for both sexes found along the roads). Some toads were found under the same trees in successive wet-seasons. Spooling showed that distances moved per night were similar along the road versus under the trees, but toads under trees showed lower net displacements. Diets also differed (based upon scat analysis), with tree toads feeding more on beetles and less on ants. These nutrient-rich hotspots are exploited primarily by adult females and juvenile toads, whereas adult males congregate at breeding sites. By magnifying pre-existing intraspecific divergences in habitat use, bird rookeries may enhance population viability of cane toads by enabling critical age and sex classes to exploit food-rich patches that are rarely used by adult males.

Building biogenic beachrock: Visualizing microbially-mediated carbonate cement precipitation using XFM and a strontium tracer

The fate of reef islands is a topic of ongoing debate in the face of climate change-induced sea-level rise and increased cyclone intensity. Increased erosion and changes to the supply of reef-derived sediment may put sand reef cays at risk of dramatic morphological changes. These changes may have negative implications for the existence of reef cay environments, which host vital sea turtle and bird rookery habitats. Beachrock, consolidated carbonate beach sediment in the intertidal zone, forms naturally on many tropical beaches and reduces the erosion rates of these beaches when compared to unconsolidated sand. In spite of the critical role beachrock plays in stabilizing some reef cay shores, the method of beachrock formation is still incompletely understood. In this investigation, beachrock was synthesized using beach sand and beachrock samples from Heron Island (Great Barrier Reef, Australia) in aquarium experiments in which natural beachrock formation conditions were simulated. Beachrock was produced in two aquaria wherein the water chemistry was influenced by microorganisms derived from the natural beachrock ‘inoculum’, whereas no cementation occurred in an aquarium that lacked a microbial inoculum and was controlled only by physicochemical evapoconcentration. The new cements in the synthesized beachrock were analyzed using synchrotron-based X-ray fluorescence microscopy and were identified using a Sr-tracer added to the experimental seawater. The resulting precipitates cement sand grains together and contain abundant microfossils of the microorganisms on whose exopolymer they nucleated, demonstrating the fundamental role microbes play in beachrock formation. These results are of interest because beachrock could be utilized as a natural coastline stabilization strategy on sand reef cays, and in turn, protect the unique habitats reef islands support.

Эколого-физиологическая характеристика растительных сообществ под птичьим базаром на Западном Шпицбергене

Эколого-физиологическая характеристика растительных сообществ под птичьим базаром на Западном Шпицбергене

Feeding preferences and responses to prey in insular neonatal Florida cottonmouth snakes

AbstractCottonmouth snakes residing on certain Gulf coastal islands of Florida feed largely by scavenging fish that are dropped or regurgitated by colonial nesting birds. Because of the relative isolation of these snakes and their long association with bird rookeries, it is of interest to inquire whether snakes exhibit any dietary preference, or whether consumption of fish remains strictly opportunistic. Here we examine whether there are differences in prey acceptance between insular and mainland naive, neonatal cottonmouths, and whether insular snakes develop preferences for particular prey items. We report that both insular and mainland snakes accept a range of similar prey items including fish, mice and lizards. We also report that naive insular neonates tend to accept fish earlier following birth than they accept mammalian prey. When naive neonates are fed only a single specific prey item, fish or mammal, during the first year of life, individuals preferentially follow odors that are associated with the sole dietary prey to which they have been conditioned. However, following conditioning on either prey category (fish or mice) these snakes also eat the non‐conditioned prey (mice or fish, respectively) when presented with the opportunity. Our results suggest that young cottonmouths might adjust foraging strategy to match prey availability, while retaining flexibility in feeding behavior based in inherent dietary breadth. Thus, the insular population can occupy a broad trophic niche while fine‐tuning foraging behaviors to match the local conditions.

Bird rookeries have different effects on different feeding guilds of herbivores and alter the feeding behavior of a common caterpillar

Aggregations of nesting birds are common in many landscapes and have a broad impact on their surrounding habitat through the nutrient input and disturbance of their guano depositions. Ecological theory makes specific predictions about how disturbances or nutrient pulses will affect the interactions between different trophic levels of organisms. This study dissects the effects of a multi-species bird rookery on plant-herbivore interactions on coast live oak trees (Quercus agrifolia). I found that different feeding guilds of herbivores were affected in opposing directions by the rookery. I observed less chewing damage within the rookery than outside, but more damage from piercing/sucking and galling herbivores within the rookery than outside. To understand why chewing guild herbivores are negatively affected by the environmental impacts of the rookery, I explored the behavioral response of a specialist caterpillar (Phryganidia californica) to various rookery conditions. Bird guano had a direct negative impact on P. californica foraging. P. californica movement was impaired by guano addition to twigs, and caterpillars preferred to eat leaves without guano on them. The rookery also had an indirect negative effect on P. californica foraging, as P. californica preferred clean leaves from forest areas outside of the rookery over clean leaves from within the rookery. This study suggests that while it may be possible to make accurate predictions about the effect of large events (such as rookery formation) on different trophic levels, understanding the response of individual species within that trophic level requires an understanding of aspects of their natural history—such as feeding mode and behavior.

Nutrient distribution across the insular shelf of La Parguera, Puerto Rico: assessment by algal tissue nitrogen

A survey was conducted to investigate possible presence of an inshore to shelf edge gradient in % nitrogen (%N) and stable nitrogen isotope ratio (δ15N; ‰ vs. air) in tissues of the rhodophyte Acanthophora spicifera and the ocrophytes Lobophora variegata and Dictyota bartayresiana in coastal waters of La Parguera, southwest Puerto Rico. Average %N (1.26 ± 0.08 SD to 3.25 ± 0.10) and δ15N (2.06 ± 0.04 to 8.16 ± 0.14‰) in Acanthophora spicifera was highly variable along the shoreline. The highest inshore values of δ15N occurred at two stations influenced by secondary sewage input and a bird rookery and lower values (0.81 ± 0.06‰) were observed at mid-shelf locations. Dictyota bartayresiana and L. variegata did not display clear trends in %N across the insular shelf; however, δ15N for Dictyota bartayresiana was significantly higher inshore (3.48 ± 0.09‰) versus mid-shelf and shelf edge (0.00 ± 0.08‰) and δ15N for L. variegata was significantly higher at mid-shelf (2.13 ± 0.25‰) versus shelf edge locations (0.34 ± 0.24‰). These results indicate that anthropogenic effects on tissue nutrients are spatially distributed across the shelf, being higher near shore and not evident at the shelf edge.

Aquatic fauna as indicators for Everglades restoration: Applying dynamic targets in assessments

Abstract A major goal of the Comprehensive Everglades Restoration Plan (CERP) is to recover historical (pre-drainage) wading bird rookeries and reverse marked decreases in wading bird nesting success in Everglades National Park. To assess efforts to restore wading birds, a trophic hypothesis was developed that proposes seasonal concentrations of small-fish and crustaceans (i.e., wading bird prey) were a key factor to historical wading bird success. Drainage of the Everglades has diminished these seasonal concentrations, leading to a decline in wading bird nesting and displacing them from their historical nesting locations. The trophic hypothesis predicts that restoring historical hydrological patterns to pre-drainage conditions will recover the timing and location of seasonally concentrated prey, ultimately restoring wading bird nesting and foraging to the southern Everglades. We identified a set of indicators using small-fish and crustaceans that can be predicted from hydrological targets and used to assess management success in regaining suitable wading bird foraging habitat. Small-fish and crustaceans are key components of the Everglades food web and are sensitive to hydrological management, track hydrological history with little time lag, and can be studied at the landscape scale. The seasonal hydrological variation of the Everglades that creates prey concentrations presents a challenge to interpreting monitoring data. To account for the variable hydrology of the Everglades in our assessment, we developed dynamic hydrological targets that respond to changes in prevailing regional rainfall. We also derived statistical relationships between density and hydrological drivers for species representing four different life-history responses to drought. Finally, we use these statistical relationships and hydrological targets to set restoration targets for prey density. We also describe a report-card methodology to communicate the results of model-based assessments for communication to a broad audience.

Pitviper Scavenging at the Intertidal Zone: An Evolutionary Scenario for Invasion of the Sea

ABSTRACT It is difficult for terrestrial vertebrates to invade the sea, and little is known about the transitional evolutionary processes that produce secondarily marine animals. The utilization of marine resources in the intertidal zone is likely to be an important first step for invasion. An example of this step is marine scavenging by the Florida cottonmouth snakes (Agkistrodon piscivorus conanti) that inhabit Gulf Coast islands. These snakes principally consume dead fish that are dropped from colonial nesting bird rookeries, but they also scavenge beaches for intertidal carrion, consuming dead fish and marine plants, and occasionally enter seawater. Thus, allochthonous marine productivity supports the insular cottonmouth population through two pathways, and one of these pathways connects the snakes directly to the sea. The trophic ecology and behaviors of this unusual snake population suggest a requisite evolutionary scenario for the successful transition of vertebrates from a terrestrial to a marine ...

Trophic Ecology of Insular Cottonmouth Snakes: Review and Perspective

Florida cottonmouth snakes (Agkistrodon piscivorus conanti) inhabit insular as well as mainland habitat, and they occur in particularly large numbers on some of the Gulf coast islands of Florida. The success of this species on islands is attributable, in part, to a broad trophic niche that encompasses many prey items including carrion. Numerous cottonmouths living on the island of Seahorse Key consume primarily dead fish that are dropped from colonial nesting bird rookeries, but they also prey on rats (Rattus rattus) that are invasive fauna on the island. While alternative prey items (e.g. lizards) are available to newborn snakes, smaller individuals also scavenge for fish carrion at early ages. Field observations indicate there is social structure during foraging events that involve multiple snakes. Occasionally, insular cottonmouths scavenge for intertidal carrion and detritus that washes onto beaches. Numerous and diverse objects of appropriate size, shape, and odor are ingested by foraging snakes, including masses of marine algae that bear fish odors. The intensive scavenging behaviors of cottonmouths appear to reflect behavioral and physiological specializations that have evolved in response to insular resource limitations. Two important pathways by which allochthonous marine productivity enters the terrestrial food web to support these insular cottonmouths are (1) colonial bird rookeries and (2) shore drift of carrion and detritus. The importance of the bird rookeries as a source of marine fish is reflected in the observation that far lower numbers of cottonmouths occur on islands that lack a bird colony. We have no evidence that the insular cottonmouths feed on the colonial nesting birds, but they consume smaller passerine species.

Foraging Cues Used by Insular Florida Cottonmouths, Agkistrodon piscivorus conanti

Abstract Previous studies have shown that snakes can use groundborne vibrations for localizing prey, and some have proposed that such vibrations provide important cues for cottonmouth snakes while foraging on fish that fall from island bird rookeries. The latter hypothesis was tested by using fish and fish models to study the behavioral response of insular Agkistrodon piscivorus conanti to groundborne vibrations and olfactory cues. Diving and wading birds that nest on Seahorse Key, a small island adjacent to the northern Florida peninsula in the Gulf of Mexico, regularly drop fish in the vicinity of resident A. piscivorus during the colonial nesting period. Here we report that presentation of an equivalent groundborne vibration, without associated chemosensory or visual stimuli, failed to induce overt foraging behavior in these snakes. However, presentation of a fish-based olfactory stimulus, without associated groundborne vibration or motion, triggered a foraging response in A. piscivorus. Snakes from tw...

Wood Stork Nesting in Georgia: 1992-2005

Wood Storks (Mycteria americana) were first recorded nesting in Georgia in 1965 at Blackbeard Island National Wildlife Refuge (Harris 1995). In 1992, biologists initiated annual aerial surveys of known wading bird rookery sites to document Wood Stork distribution and estimate the number of nesting pairs in Georgia. Additionally, personnel from the U.S Fish and Wildlife Service and Savannah River Ecology Laboratory have contributed annual ground-count data for several colonies. Since surveys began, stork nesting has been documented at least once in 43 locations across the Coastal Plain of the state, with an average of 14 active sites per year. The documented nesting effort for storks has increased from four pairs in one wading bird colony in 1965 to a high count of 1,817 pairs in 19 colonies in 2005. A regression of log-transformed nest totals for the 14-year time-series (1992-2005) showed no significant overall trend in nesting pair numbers (P = 0.84) for that period. However, it is possible that an ongoing rebound from a drought-related crash could continue, resulting in an increasing trend. Thirty-three (77%) of stork nesting locations were on private land, with only ten (23%) nesting locations in public ownership. Seven colony sites have supported an average of 68% of the stork nesting effort since 1992; in 2005 these sites supported 77% of the nesting effort. Although not a systematic census of all potential stork nesting habitat, these standardized surveys have produced a useful estimate of Wood Stork population size, distribution, and stability in Georgia. We believe that Georgia’s Wood Stork population has shown an increase in size and distribution, and that numbers can continue to increase or stabilize as long as hydrologic conditions favorable to the species persist.

Within-season Nest Persistence in Large Wading Bird Rookeries

Within-season nest persistence of large wading bird (Ciconiiformes) rookeries in the Atchafalaya Delta, Louisiana was examined during 1994 and 1995. A sample of rookery trees was permanently marked, and the status of 7,864 nests of ten species was followed through time. Nest construction began in early March, and some rookeries were still active into September during both seasons. Uniform nest persistence rates were calculated for each 28-day time period throughout the nesting season. Nest persistence rates per 28 days ranged from 0.00-0.96. During both years the rates tended to be lowest during the early season and increased into the late season. In 1994, nest persistence rates were significantly different, caused by the interaction of season and late nesting of White Ibis. In 1995, nest persistence rates differed significantly by season. The results call into question the value of nest counts obtained by one visit to a rookery complex, as these may greatly underestimate the numbers of breeding birds.

Bryophyte Vegetation and Habitat Gradients in the Tikhaia Bay Region, Hooker Island, Franz Josef Land, Arctic Russia

A quantitative analysis of contemporary moss assemblages is presented for forty-seven bryophytes occurring in 31 sites in the Tikhaia Bay region of northwestern Hooker (Gukera) Island, Franz Josef Land Archipelago. Fifteen (31%) of these species were found in only one site and 7 (15%) species were found in only two sites. Two-way indicator species analysis, TWINSPAN, resulted in three major species groups. Canonical correspondence analysis, CCA, results showed species distribution patterns correlated with major environmental variables of moisture, slope, fertilized sites, and exposure. The three species groups are projected on the CCA ordination. Group 1 dominates steep, rocky, fertilized slopes with northern exposures while group 3 is at the other extreme of these variables. Group 2 is intermediate along these variables and spans the moist-dry habitat gradient. Bryophytes are an important component of the vegetated surfaces in the northernmost arctic islands. The large dome ice caps on the Franz Josef Land islands result in limited exposed terrestrial habitats. Most surfaces are covered by snow, ice, and glaciers. Only south-facing sites below active bird rookeries are dominated by vascular plant communities. The remaining vegetated surfaces in the exposed, ice-free sites are dominated by rich non-vascular plant communities. In contrast to only 57 vascular plants reported for the islands, a total of 102 mosses, 55 liverworts, and 115 lichens have been reported by Aleksandrova (1983). Her list of bryophytes for the archipelago was compiled using Fischer (1896), Hanssen and Lid (1932), Palibin (1903), Safronova (1983), Tikhomirov (1948), Tolmachev (1931), and Tolmachev and Shukhtina (1974). The first reports of bryophyte collections in the Archipelago were published as a result of the Jackson-Harmsworth Expedition in 1894-1897. Five bryophytes were identified (Fischer 1896). It was not until 30 years later that the Russian Sedow expedition of 1929 and 1930 explored the Archipelago. This more extensive study was published in Russian and summarized in French. It described 83 mosses and 7 liverworts (Savicz 1936). Simultaneously in 1930, the Norwegian sealer, Bratvaag, of Alesund explored Aleksandra and Prins Georga Islands. This expedition found a total of 25 taxa of bryophytes (Stormer 1940). This paper reports on results from the 1991 Norwegian-Russian-Polish expedition to the Tikhaia Bay region in Franz Josef Land. This was the first opportunity for a western botanist to enter the archipelago since 1930. The purpose of this study was, for the first time, to describe some of the environmental factors that influence bryophyte distributions in the extreme arctic habitats of Tikhaia Bay region in the Franz Josef Land Archipelago. To accomplish this goal all species of all the exposed major habitats were collected and seven environmental parameters were recorded. Further, the second purpose was to summarize the findings in the form of a multivariate analysis. The resulting species-environment relationships are inferred from community composition data and associated environmental scalar values.

Patterns of Herbivory in Belizean Mangrove Swamps

We quantified herbivory on leaves of two mangrove species, Rhizophora mangle and Avicennia germinans, at eight sites in Belize. Amounts and types of damage were compared among three mainland sites and five mangrove cays off the coast. Several environmental and autecological factors that potentially influence herbivory were examined, including canopy cover, tree age, leaf age, tidal height, and nutrient enrichment. Herbivores damaged 4.3 percent to 25.3 percent of Rhizophora leaf area and 7.7 percent to 36.1 percent of Avicennia leaf area, figures comparable to other mangal throughout the world. On average, Avicennia was less frequently damaged than Rhizophora at all sites but one. Herbivory at a bird rookery was not significantly higher than elsewhere, indicating that nutrient enrichment of leaves did not stimulate herbivory at this site. Significant but inconsistent differences in damage were detected between the cays and mainland sites. Significant differences, dependent on tidal height, were found between seedlings and trees. Rhizophora seedlings growing under a canopy of adult conspecifics suffered twice as much damage as seedlings growing in areas where the adult canopy was removed. Damage types occurring on each species were consistent across all sites, but the two species did not share the same herbivores.

Residual Influence of Macronutrient Enrichment on the Aquatic Food Web of an Okefenokee Swamp Abandoned Bird Rookery

We present evidence for residual nutrient enrichment of diverse components of a blackwater marsh, by a biotic component of the ecosystem itself. Thousands of nesting white ibis (Eudocimus albus) that foraged over a 20-km radius fertilized a rookery with guano within Okefenokee Swamp, Georgia, USA. One to two yr after the birds abandoned it, this marsh showed continued enrichment effects. Elevated available phosphorus in sediments, as measured by equilibrium phosphate concentration, contributed to enhanced biomass of phytoplankton in the overlying water column. Planktivorous fish were greater in biomass than at reference sites. Experimental phosphorus and nitrogen fertilization of enclosures at a reference site (at levels representing residual enrichment after birds had left) caused zooplankton biomass to increase significantly. These results demonstrate that this blackwater ecosystem was macronutrient limited, and manifested residual enrichment effects of wading birds on sediments, and a positive effect of sediments on phytoplankton. Results also suggest further indirect positive effects of birds on higher trophic levels (zooplankton and fish), via macronutrient transfers.

Okefenokee marshland before, during and after nutrient enrichment by a bird rookery

Field measurements and data from the literature were used to construct a trophic model of Okefenokee Swamp marshland. Seasonal data were used to check dynamics of the model before, during and after simulated nutrient input from wading bird guano. The model gives reasonable estimates of the effects of enrichment on benthic detritus, aquatic macrophytes and phytoplankton, and conservative estimates of the increase of zooplankton and fish stocks. Simulated levels of the above components decreased toward nominal states after simulated abandonment by birds, and the rates of decrease generally followed field trends that were measured. The model indicates that nesting wading birds can have considerable effects on aspects of an aquatic ecosystem that are not normally associated with them (such as benthic detritus and fish). Significant links between components of aerial and aquatic systems are thus brought to light.

High-performance liquid chromatographic isolation of uric acid from soil for isotopic determination

Uric acid was extracted from soil into potassium phosphate solution and isolated from other components by high-performance liquid chromatography, then the isolated fraction was subjected to nitrogen isotope analysis. Studies of the adsorption of uric acid on clay indicated no significant isotope fractionation during the exchange reaction; hence the isotope ratio found in the extract was the same as that in the soil. An increase in soil ammonia content followed the decomposition of uric acid. No uric acid isotopic preference by uric acid bacteria during the decomposition was found. The fractionation at the time of ammonia evaporation was mainly responsible for the high nitrogen isotope ratio in bird rookeries. An extremely high ratio for soil ammonia was found in a simulation experiment. This phenomenon may be mimicked in nature.