Audouin's Gull Research Articles

Food availability and nest predation influence life history traits in Audouin's gull, Larus audouinii.

The effects of food availability and nest predation on several life history traits such as adult survival, dispersal, and reproductive performance were assessed in an Audouin's gull (Larus audouinii) colony during the period 1992-1997. The amounts of fish discarded from trawlers were used as a measure of food availability, and a trawling moratorium which partially overlapped with the breeding season of the gulls was taken into account. The effects of nest predation were assessed in 1994, when a terrestrial predator entered the colony and remained for the whole breeding season preying on both eggs and chicks. Using the moratorium and the predatory event as natural experiments, several hypotheses were tested: (a) food supply would affect breeding performance but not adult survival (independently of age and sex), since gulls are long-lived and adult survival is the most sensitive demographic parameter in their population dynamics; (b) the predator would trigger breeding dispersal (although gulls are mostly philopatric, they are known to abandon their natal colony after breeding failure instigated by events such as this). If breeding dispersal occurs, the rate is expected to be higher in females than in males, and higher in new breeders than in more experienced breeding birds, as is usually recorded in colonial seabirds. Probabilities of resighting and survival were estimated separately, using capture-recapture models. As expected, changes in food availability did not affect adult survival, whereas they influenced egg volume, clutch size, and breeding success. Local adult survival was estimated to be 0.908 (SD = 0.007) for males and females, and it did not change significantly with the age of individuals (range 3-8 years). The predator significantly decreased breeding success, and caused the dispersal of a number of adults probably to breed in another colony; this rate was estimated at an average of 0.10 (SD = 0.02). As expected, inexperienced breeders dispersed significantly more (14%) than more experienced breeders (8%) after the predator event, but dispersal was not sex biased. Recapture probabilities after the predator event suggest that birds that left the colony still had not returned. Results confirm that population dynamics of ground-nesting seabirds are sensitive to terrestrial predation, even when predation caused only a partial breeding failure.

Recruitment of Audouin's gull to the Ebro Delta colony at metapopulation level in the western Mediterranean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 180:267-273 (1999) - doi:10.3354/meps180267 Recruitment of Audouin's gull to the Ebro Delta colony at metapopulation level in the western Mediterranean Daniel Oro1,2,*, Roger Pradel1 1CEFE, CNRS, 1919 route de Mende, F-34293 Montpellier cedex 5, France 2Dept. Biologia Animal, Vertebrats, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain *Present address: Applied Ornithology Unit, Division of Environmental and Evolutionary Biology, Graham Kerr Building, Glasgow University, Glasgow G12 8QQ, United Kingdom. E-mail: doro001@udcf.gla.ac.uk ABSTRACT: Few studies have been carried out on movements among local populations of long-lived birds due to the difficulty of marking and following individuals in different populations within a metapopulation for the long term. An extensive long-term ringing programme carried out in most of the local breeding populations (i.e. colonies) within the western Mediterranean metapopulation of Audouin's gull allowed us to assess the probability of a gull being recruited into the Ebro Delta colony according to the colony of birth. The studied metapopulation includes 93% of total world population of breeding pairs. Resights of 1302 ringed breeders during 1 breeding season at the Ebro Delta were used to model the probability of recruiting as a function of distance from the natal colony. A negative binomial distribution accounting for overdispersion was fitted in the framework of generalized linear models. Distance explained 97% of the difference among colonies which themselves accounted for 67% of the total deviance. Recruitment probability decreased exponentially with distance from the Ebro Delta colony, despite the high movement capabilities of the species during the breeding and non-breeding seasons. However, dispersal was recorded even from the most distant colony at 655 km from the Ebro Delta, although at a very low rate. Results agree with the prediction of several theoretical models of animal movement that distance is one of the most important determinants of dispersal and colonization rates within metapopulations. KEY WORDS: Audouin's gull · Recruitment · Metapopulation · Distance · Colony growth · Population dynamics Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Body size variation in Audouin's Gull Larus audouinii; a density‐dependent effect?

A significant decrease in the body size of Audouin's Gulls Larus audouinii breeding at the Chafarinas Islands is reported. The decrease in linear measurements in the current breeding population ranged from 2.5% to 5.6% in males and from 0.61% to 4.4% in females. This was detected when assessing the reliability of a sex‐discriminating function derived for the same colony 13 years earlier. When applied to the current population, this function failed to predict the sex of a large proportion of males (44%). The relative decrease in mean size was significantly greater in males than in females for culmen, nalospi and tarsus lengths, while for bill depth at culmen, wing length and body mass the relative decrease was similar in both sexes. Since the extent of differences depended on sex, these differences cannot be attributed to a systematic between‐observer bias. Mean body size reduction might be either the result of a greater proportion of small breeding birds in the current population, because of increased availability of nesting sites (competition relaxation hypothesis), or an outcome of environmental factors affecting growth parameters (environmental constraint hypothesis). According to the first hypothesis, the changes observed would be associated with higher variability values. Conversely, if the second is true, the degree of variability should be similar. Since there are no significant differences in the degree of variability shown in the two data sets, our results support the second hypothesis. The environmental constraint acting via growth parameters is probably related to the increase in the number of Audouin's Gull breeding pairs while food availability was depleted. Our data suggest that changes in the duration of the growth period, rather than in the growth rates themselves, are involved in the body size differences found.

Trophic niche width and overlap of two sympatric gulls in the southwestern mediterranean.

The diets of two potential competitor species, Audouin's Larus audouinii and yellow-legged gulls Larus cachinnans, were examined while they bred at the Chafarinas Islands during 1993, 1994, and 1995. Data were collected during two commercial fishing regimes: (1) trawling and purse seine fisheries, and (2) diurnal trawlers only. Since the food supply for the gulls in this area was heavily reliant on the activity of purse seine fisheries, these contrasting situations allowed us to analyze short-term effects, induced by daily changes in food supply, on niche width, dietary shift, and niche overlap between the two species. Overall, both species relied mainly on fish for food, especially Clupeiforms, in the case of Audouin's gull irrespective of the fishing situation, and in the case of the yellow-legged gull, only when purse seine fishing was in operation. When purse seine boats did not operate (food shortage), yellow-legged gulls broadened their niche, consuming equal amounts of all the feeding resources, and they showed a dietary shift toward a greater consumption of prey from refuse tips. In contrast, Audouin's gulls did not change their niche width, but showed a slight dietary shift away from the consumption of epipelagic fish, compensated by an increase in reliance on benthic-mesopelagic resources. Niche overlap was clearly higher on days when both fishing fleets operated, probably because a superabundant food resource facilitates high overlap without affecting coexistence between the two species. Since our study was developed on the basis of daily variations in food supply, and competition effects are to be expected on a longer-term basis, these changes can be seen as the outcome of the coexistence of two species in stable competitive equilibrium.

Exploitation of trawler discards by breeding seabirds in the north-western Mediterranean: differences between the Ebro Delta and the Balearic Islands areas

Local trawler fisheries operate around the seabird colonies of the Ebro Delta and Majorca. The use made of the discards produced by this fishery by scavenging breeding seabirds was examined from 1992 to 1996. All breeding species at each site (except little terns at the Ebro Delta) were observed following trawlers while fishermen were discarding fish: Audouin's, yellow-legged, lesser black-backed, black-headed and slender-billed gulls, common and Sandwich terns in the Ebro Delta area; and Audouin's and yellow-legged gulls, Cory's and Balearic shearwaters, storm-petrel and common shags in the Majorca area. Some non-breeding seabird species, such as gannets, skuas, and Chlydonias spp. terns were also recorded in small numbers. Nevertheless, species diversity of the seabird community associated with trawlers was significantly higher at the Ebro than at Majorca, because Procellariiformes, which breed only in the latter area, were displaced by large numbers of gulls. In Majorca, Audouin's gull was significantly more abundant than expected from the size of its breeding population, and in the Ebro area the same was true for the lesser black-backed gull, the black-headed gull, and the common tern. However, the success rates of feeding on trawler discards were not related to species' Presence Indices. In the Ebro area, Audouin's gull took greatest advantage of discards, whereas in Majorca only the yellow-legged gull consumed significantly higher amounts of discards than expected from its Presence Index. The consumption rate of fish discards was significantly higher in the Ebro area (72%) than in the Majorca area (64%). Although the size of fish consumed was associated with seabird body mass, most of the discard items were of a suitably small size. Crude estimates of the weight of fish discarded throughout a breeding season suggest that seabirds, especially Audouin's gulls at the Ebro Delta, may obtain a substantial part of their energy demands from this fishery, while discard availability at the Balearic Archipelago does not support the energy requirements of seabirds breeding there.

Bias Associated with Diet Samples in Audouin's Gulls

We analyzed five different types of food samples from Audouin's Gull (Larus audouinii), collected during the breeding seasons of 1994 and 1995 at its two main breeding colonies, the Ebro Delta and the Chafarinas Islands. These food samples included spontaneous regurgitates, dry boli containing partially digested food, food remains, pellets, and prey identified during direct observations of chick provisioning. We compared estimates of biomass, levels of taxonomic determination allowed by each kind of food sample, and the associated potential biases to assess which sampling method provides the best estimate of diet in gulls. Regurgitates allowed identification of most prey to species level and reliable biomass estimates, but their collection was time-consuming and invasive. Dry boli provided almost the same information as regurgitates at order level and were easy to collect. However, both underestimated soft-bodied prey and prey with large, hard parts. Food remains provided an estimate of diet composition that was highly biased towards prey with large distinctive hard parts. However, food remains were a good complement to dry boli, enhancing biomass estimates for food items that had a good relationship of weight and linear measurements of prey..hard parts. Direct observation allowed identification of prey only to upper taxonomic categories, and is useful when only a broad categorization of prey types is required. Pellets showed important biases towards fish with robust otoliths, and inaccurate conversion to biomass, but they can be useful for monitoring variations in the consumption of certain prey items. Several factors such as time spent collecting, sample availability, disturbance to animals, and the status of the species studied need to be considered when deciding on a method of diet assessment sampling.

Inter- and Intraclutch Variability in Heavy Metals and Selenium Levels in Audouin's Gull Eggs from the Ebro Delta, Spain

Heavy metal (Zn, Cu, Mn, Cd, Pb, Hg) and Se concentrations were analyzed in 57 Audouin's gull (Larus audouinii) eggs belonging to different clutch sizes. Inter- and intraclutch variability in metal concentrations was investigated as a potential source of bias in the assessment of pollution levels. Moreover, we analyzed the relationship between metal levels in the shell and in the contents, to evaluate the reliability of museum eggshells as indicators of historical changes of these pollutants. An outstanding female effect and/or a laying order effect underlies egg Hg levels; the fact that eggs in a clutch are not independent observations needs to be taken into account both when designing sampling strategies and when performing any analysis or interpretation of the results. The relationship between Hg in shells and contents is not sufficiently accurate to allow the use of egg-shell concentration as a reliable predictor of egg-contents concentration. However, if changes in the ecosystems are large enough it could be used to trace gross historical trends of these pollutants.

Influence of food availability on interactions between Larus cachinnans and L. audouinii

Predatory and (or) kleptoparasitic interactions are greatly facilitated in mixed-species gulleries, particularly when one of the species is larger than the others. Larus audouinii, the Audouin's gull, is a threatened species breeding in sympatry with the larger L. cachinnans, the yellow-legged gull, throughout the Mediterranean. The yellow-legged gull has often been cited as the main threat to the Audouin's gull. On the Chafarinas Islands, the second largest breeding place for Audouin's gulls in the world, both gull species depend largely on commercial fisheries for food. We analyze the influence of food availability, assessed through fishery activity, on the frequency and intensity of interaction pressure by yellow-legged gulls upon Audouin's gulls during the breeding season. We studied five different types of interaction: (1) flyovers of yellow-legged gulls; (2) ground intrusions; (3) egg predation; (4) chick predation, and (5) aerial kleptoparasitism. Moreover, intensity of interaction pressure was assessed using logistic regression analysis to build a model of the"relationship between Audouin's gulls' response to yellow-legged gull flyovers as a dependent variable and fishing fleet activity as an independent variable. All interactions except aerial kleptoparasitism were significantly more frequent during days without sardine fishery activity. However, chick predation is significantly higher only during the period when yellow-legged gull has fledglings. Overall, the results of the estimated logistic model indicate a positive association between depleted food and the response by Audouin's gulls to aerial intrusions.

Differences in Diet, Population Size and Reproductive Performance between Two Colonies of Audouin's Gull Larus audouinii Affected by a Trawling Moratorium

discards caused by the moratorium and the likely decrease of clupeiform populations have affected both the feeding and breeding biology of the species. However, the effects of a reduced food supply were greater in the Columbretes Is., probably because of the lack of alternative food resources. When trawlers operated, the gulls' diet was very similar in the two colonies, but when the moratorium started, significant differences were found at both taxonomic and typologic levels. Prey from rice fields acted as a buffer for the Ebro Delta colony, whereas in the Columbretes Is. the gulls were forced to fish actively, probably at greater energy costs. In the moratorium years, breeding success was always significantly lower in the Columbretes Is. than in the Ebro Delta; extremely, no young fledged in the Columbretes Is. in 1993. Clutch size was also significantly lower in the Columbretes Is. colony, even when the moratorium did not coincide with the laying stage, suggesting that predation by Yellow-legged Gull Larus cachinnans could be an additional limiting factor at this locality, where the ratio of breeding pairs of Yellow-legged to Audouin's Gulls is much higher than in the Ebro Delta. In contrast to previous studies, the larger colony (Ebro Delta) had better breeding performance than the smaller colony (Columbretes Is.), suggesting that density-dependent effects may not operate in the Ebro Delta colony because of the large variety of foraging habitats (rice fields, lagoons, dunes, beaches) and the high productivity of the sea off this colony. While population size in the Ebro Delta colony suggested the absence of limiting factors until the establishment of the trawling moratorium, the size of the Columbretes Is. colony indicated a breeding site limitation, and probably competition with the Yellow-legged Gull.

Interspecific kleptoparasitism in Audouin's Gull Lams audouinii at the Ebro Delta, northeast Spain: a behavioural response to low food availability

Kleptoparasitism of Audouin's Gull Lams audouinii on other seabirds, a foraging behaviour previously unrecorded for the species, was studied in the Ebro Delta, northeast Spain, during 1992. The relationship between kleptoparasitism and trawler activity was assessed through changes in the availability offish discards brought about by a trawling moratorium. When trawlers are not active, Audouin's Gulls use different feeding strategies, such as interspecific kleptoparasitism. Audoin's Gulls appeared to prefer to kleptoparasitize terns rather than gulls, but the success rate on gulls was higher. Most of the attacks rather than gulls, but the success rate on gulls was higher. Most of the attacks were performed by single Audouin's Gulls, although success per attack improved with group size. During the trawling moratorium, the existence of large seabird colonies in the Ebro Delta acted as a buffer for Audouin's Gull through kleptoparasitism, compensating partly for the reduced food supply.

The use of chorioallantoic membranes as predictors of egg organochlorine burden

AbstractThe distribution of organochlorine pollutants between yolks, embryos, and chorioallantoic membranes (CAMs) in pipping eggs of Audouin's gulls from the Ebro Delta was determined to assess the usefulness of CAMs as surrogates for predicting whole egg pollutant burdens. The reliability of predictions was checked using a concordance analysis based on four different parameters. The most abundant pollutants found were PCBs and DDTs, whereas levels of HCHs were much lower. Generally, the largest concentrations of contaminants were found in yolk sacs, followed by embryos and CAMs. The latter contained only 1.21% of the total concentration of organochlorines detected. Results show that CAMs could provide good predictions only for those pollutants being almost completely excreted to the CAM (e.g., hexachlorocyclohexanes, PCB52, and DDD). In the other organochlorines tested, the prediction obtained is too weak to recommend the use of CAMs for the estimation of their total burden in the eggs of Audouin's gull. This suggests that the reliability of CAMs as surrogates should be tested for each chemical and species, prior to their use in nonlethal monitoring programs.

Influence of trawling activity on the breeding ecology of a threatened seabird, Audouin's gull Larus audouinii

The ~nfluence of a trawling moratorium on the breedlng ecology of Audouin's gulls (Larus audouinii Payraudeau) was investigated during 1992 and 1993 in the largest colony of the species in the world (70% of total population), at the Ebro Delta, NE Spain. western Mediterranean. In this colony, Audouin's gull behaves partly as a scavenger following the trawling fleet and exploiting fishing discards. Each year, the trawling moratorium affected different breeding stages of the species: in 1992 it overlapped with pre-laying and laying stages, while in 1993 it affected most of the chick-rearing stage. We examined differences in laying dates, laying interval, clutch and egg slzes, nest desertion during laying, hatching success, hatchling mass and condition, growth rates, chick survival and breeding success. The moratorium greatly affected egg production in 1992, delaying the start of l ay~ng and dramatically decreasing clutch and egg sizes. Intraclutch egg size variation between the 2 years suggests that egg size profiles are outcomes of the interaction between physiological and environmental factors rather than the result of ultimate factors. Nest desertion was much higher in 1992, probably because some females were under a critical body condit~on threshold and they deserted after laying the first egg. Hatching success also decreased significantly during 1992, probably related to changes in the size and the quality of the eggs. Chick growth and survivorship was h ~ g h e r in 1992, when trawler discards were normally available, than in 1993. Trawler discard availability during chick rearing was more important than egg size in determining chick survival. However, differences were not always significant, since In 1993 the n~oratorium did not start until the chicks were 1 wk old, and, further, chicks had h ~ g h e r skeletal size and body condition (in order of Importance) than In 1992. In fact, chicks had similar fledgling condition in both years at the end of the reanng stage. In 1993, the overall breeding success decreased by 4 8 % Nevertheless, gulls' breed~ng performance for the 2 years was much lower than before the establishment of the flrst moratorium In 1991, and the situation suggests that clupeo~ds, the prey on wh.ich Audouin's gull feed, are scarce. It seems that gulls were not able to compensate for the lack of trawler discards during egg production, since the avallablllty of secondary feeding resources was much lower in March and April (pre-laying and laying stages) than in June (chick-rearing stage). Although in long-lived species a decrease in food supply should affect fecundity before affecting adult survival, results confirm the importance of the trawler fleet activity for the conservat~on of this threatened species.

Changes in Foraging Range of Audouin's Gulls Larus audouinii in Relation to a Trawler Moratorium in the Western Mediterranean

Changes in Foraging Range of Audouin's Gulls Larus audouinii in Relation to a Trawler Moratorium in the Western Mediterranean

Audouin's GullsLarus audouinii associate with sub-surface predators in the Mediterranean Sea

Two observations of Audouin's Gull flocks foraging on small fish forced to rise to the sea surface by tunas are presented. Observations were made just off-shore in the Ebro Delta, and Audouin's Gulls and terns concentrated in these flocks more than other seabirds breeding there, probably due to their higher ability for catching fish actively. The association of Audouin's Gulls with sub-surface predators may be a supplementary foraging behaviour for the species, especially during periods of short food supply.

Dioxins, furans and AHH-active PCB congeners in eggs of two gull species from the Western Mediterranean

Polychlorinated biphenyls, dibenzodioxins and dibenzofurans were analysed in eggs of a protected gull species, the Audouin's Gull ( Larus audouinii) and compared to those of the Yellow-legged Gull ( Larus cachinnans), both breeding in the Western Mediterranean (Ebro Delta and Medes Islands, respectively). Differences in concentrations as well as in congener profiles reflected differences in both habitat and diet of the two species. Levels of AHH-active PCB congeners were lower in Yellow-legged Gull (0.4–1.6.μg/g d.w) than in Audouin's Gull eggs (1.2–33.9 μg/g d.w.). These concentrations, expressed in international toxic equivalence factors (i-TEQ/g d.w.), were on average 24 times higher in the Audouin's gull. I-TEQ levels due to dioxins were also higher in this species by a factor of ca. 7. I-TEQ levels related to PCBs resulted 90–230 times higher than those of dioxins and furans. Thus, AHH-inducing PCBs might represent even higher toxicological hazards than dioxins and furans to some populations of seabirds. The necessity of assessing the impact of these compounds in rare and protected species is pointed out.

Relationships between Fishery Activities and Presence of the Audouin's Gull (Larus audouinii) in the Columbretes Islands

-This study presents quantitative evidence for a link between the timing of fishery activities and movement patterns of Audouin's Gull, Larus audouinii, in the Mediterranean Sea. The study was conducted in 1992 and 1993 in the Columbretes archipelago, Natural Reserve (Castell6n, Spain). The diurnal pattern of Audouin's Gulls presence on the island differed significantly between fishing and non-fishing days. Most gulls abandoned the island to visit the trawlers during the hours in which they were hauling back nets near the colony. In contrast, the majority of gulls remained in the roosting area during the non-fishing days. This study shows that Audouin's Gulls derive food from commercial fishing activities, but the extent to which this threatened species depends on the fishery remains unknown. Received 7 December 1994, accepted 10 February 1995.

MIGRATION AND DISPERSAL OF AUDOUIN'S GULL LARUS AUDOUINII FROM THE EBRO DELTA COLONY

Summary Oro, D. & Martinez, A. 1994. Migration and dispersal of Audouin's Gull Larus audouinii from the Ebro Delta colony. Ostrich 65:225-230. Migratory paths and dispersal patterns of Audouin's Gulls (Larus audouinii) born in the Ebro Delta have been studied, as well as their degree of philopatry. The gulls always disperse southwards from the colony, and only the juveniles seem to disperse in other directions. Dispersal patterns of 2y, 3y and older gulls are similar, wintering mainly on Iberian Mediterranean and Moroccan Atlantic coasts. Juveniles migrate before the rest of the age classes and they winter south of older gulls, in the Senegambia region. However, conclusions on Audouin's Gulls movements are difficult to draw, owing to the large differences in resighting and recovery efforts. Data presented also suggest that Audouin's Gulls do not appear to breed before the age of four years.

Levels of chlorinated insecticides, total PCBs and PCB congeners in Spanish Gull eggs

Eggs from Herring Gulls, Audouin Gulls and Gull Billed Terns were collected at three different locations in Spain during the breeding season of 1988. Organochlorine pesticides, total polychlorinated biphenyls (PCBs) and seven selected individual chlorobiphenyl congeners were determined in each of the thirty infertile eggs. The levels of DDE and total PCBs in eggs from the Delta Ebro River are greater than those gathered at Chafarinas Island and Cuenca. Among the species investigated, the Gull Billed Tern eggs showed the lowest level followed by the Herring Gull and the Audouin Gull eggs. The levels of the seven congeners of PCBs showed that 138 was the most prominent, followed by, in decreasing order, 153, 180, 170, 101, 151, and 194. Congener 138 constituted 10.5% ± 2.7 (S.D) of the total PCBs concentration, the 153 8.7% ± 4.2, the 180 7.5% ± 1.9, the 170 3.2% ±1.0, the 101 1.9% ± 3.06, the 151 1.1% ± 1.5 and the 194 0.9% ± 0.5. Polychlorinated biphenyl (PCB) residues (48 congeners) from gull eggs gathered at Ebro Delta and Chafarinas Islands were analyzed with SIMCA (Soft Independent Modeling of Class Analogy), a principal components analysis technique. A series of technical Aroclors® were also analyzed to provide a reference data set for pattern recognition. Environmental PCB residue profiles differed according to the sample's origin. This analysis discriminated between the two regions sampled.

An assessment of pollutants in eggs of audouin's gull ( Larus audouinii), a rare species of the Mediterranean sea

Audouin's gull ( Larus audouinii) is a very rare species endemic to the Mediterranean basin. A sub-population of an estimated 130 pairs is breeding in the Tuscan Archipelago, an area heavily polluted by mercury and chlorinated hydrocarbons. Here we present the data from 5 years spent monitoring the contaminant levels in the eggs of this species. Mercury, selenium, polychlorobiphenyls (PCBs) and DDE concentrations are two to five times higher than in similar species, such as the yellow-legged herring gull, nesting in the same area. The annual trends in these contaminant levels are discussed. In view of the endangered status of Audouin's gull, there is a need to observe closely the developing trend of contamination in this species.

Audouin's gull and the Chafarinas Islands Game Reserve

The breeding population of Audouin's gull, a Red Data Book species, is endemic to the Mediterranean. Its population was estimated at 4000 pairs in 1985, but its restricted distribution and vulnerability to disturbance and competition necessitate active conservation measures. The gull's most important breeding colony is on Rey Island in the Chafarinas group, and in 1983 a three-year study was started to discover the factors limiting the size of the colony and to formulate a management plan.