The Role of Behavior in Recent Avian Extinctions and Endangerments

Abstract: Understanding patterns of differential extinction and predicting the relative risks of extinction among extant species are among the most important problems in conservation biology. Although recent studies reveal that behavior can be a critical component in many species' extinctions or endangerments, current approaches to the problem of predicting extinction patterns largely ignore behavior. I reviewed how behavior can affect population persistence and then used recent avian extinctions and endangerments to illustrate behaviors relevant to extinction risk. Behaviors that affect population persistence can be grouped as aggregation, interspecific responses, dispersal, habitat selection, intraspecific behavior, and maladaptive behavior. Behavior that can affect extinction risk is not limited to birds; for example, in many taxonomic groups (vertebrate and invertebrate) there is evidence of socially facilitated reproduction in colonial species, Allee effects on reproductive success and survival, behavioral regulation of population size, and conspecific attraction to breeding sites. Incorporating specific behaviors into models predicting extinction probabilities and patterns should improve their predictions.     

Demographic Consequences of Terrestrial Habitat Loss for Pool‐Breeding Amphibians: Predicting Extinction Risks Associated with Inadequate Size of Buffer Zones

Abstract: Much of the biodiversity associated with isolated wetlands requires aquatic and terrestrial habitat to maintain viable populations. Current federal wetland regulations in the United States do not protect isolated wetlands or extend protection to surrounding terrestrial habitat. Consequently, some land managers, city planners, and policy makers at the state and local levels are making an effort to protect these wetland and neighboring upland habitats. Balancing human land‐use and habitat conservation is challenging, and well‐informed land‐use policy is hindered by a lack of knowledge of the specific risks of varying amounts of habitat loss. Using projections of wood frog (Rana sylvatica) and spotted salamander (Ambystoma maculatum) populations, we related the amount of high‐quality terrestrial habitat surrounding isolated wetlands to the decline and risk of extinction of local amphibian populations. These simulations showed that current state‐level wetland regulations protecting 30 m or less of surrounding terrestrial habitat are inadequate to support viable populations of pool‐breeding amphibians. We also found that species with different life‐history strategies responded differently to the loss and degradation of terrestrial habitat. The wood frog, with a short life span and high fecundity, was most sensitive to habitat loss and isolation, whereas the longer‐lived spotted salamander with lower fecundity was most sensitive to habitat degradation that lowered adult survival rates. Our model results demonstrate that a high probability of local amphibian population persistence requires sufficient terrestrial habitat, the maintenance of habitat quality, and connectivity among local populations. Our results emphasize the essential role of adequate terrestrial habitat to the maintenance of wetland biodiversity and ecosystem function and offer a means of quantifying the risks associated with terrestrial habitat loss and degradation.     

Iteroparity in the variable environment of the salamander Ambystoma tigrinum

Simultaneous estimation of survival, reproduction, and movement is essential to understanding how species maximize lifetime reproduction in environments that vary across space and time. We conducted a four-year, capture-recapture study of three populations of eastern tiger salamanders (Ambystoma tigrinum tigrinum) and used multistate mark-recapture statistical methods to estimate the manner in which movement, survival, and breeding probabilities vary under different environmental conditions across years and among populations and habitats. We inferred how individuals may mitigate risks of mortality and reproductive failure by deferring breeding or by moving among populations. Movement probabilities among populations were extremely low despite high spatiotemporal variation in reproductive success and survival, suggesting possible costs to movements among breeding ponds. Breeding probabilities varied between wet and dry years and according to whether or not breeding was attempted in the previous year. Estimates of survival in the nonbreeding, forest habitat varied among populations but were consistent across time. Survival in breeding ponds was generally high in years with average or high precipitation, except for males in an especially ephemeral pond. A drought year incurred severe survival costs in all ponds to animals that attempted breeding. Female salamanders appear to defer these episodic survival costs of breeding by choosing not to breed in years when the risk of adult mortality is high. Using stochastic simulations of survival and breeding under historical climate conditions, we found that an interaction between breeding probabilities and mortality limits the probability of multiple breeding attempts differently between the sexes and among populations.     

Investigating Potential for Depensation in Marine Turtles: How Low Can You Go?

Abstract:  Where mechanisms inherent within the biology of a species affect individual fitness at low density, demographic-scale depensation may occur, hastening further decline and leading ultimately to population extirpation and species extinction. Reduction in fertility at low population densities has been identified in marine and terrestrial species. Using data on hatch success and hatchling-emergence success as proxies for fertilization success, we conducted a global meta-analysis of data from breeding aggregations of green turtles ( Chelonia mydas ) and loggerhead turtles ( Caretta caretta ). We found that there has been no reduction in fertility in small nesting aggregations in either of these species worldwide. We considered mechanisms within the mating strategies and reproductive biology of marine turtles that may allow for novel genetic input and facilitate enhanced gene flow among rookeries. Behavioral reproductive mechanisms, such as natal philopatry and polyandry, may mitigate potential impacts of depensation and contribute to the resilience of these species.     

Intermorph breeding and the potential for reproductive isolation in polymorphic mole salamanders (Ambystoma talpoideum)

The study of reproductive isolation as a prerequisite to sympatric speciation has been limited by the focus on species that have already experienced such isolation. However, a complete understanding of how such processes evolve depends on observing taxa before they complete the speciation process. We studied the potential for sexual isolation in the polyphenic mole salamander, Ambystoma talpoideum, using a series of laboratory and field experiments. This species consists of aquatic paedomorphic adults and terrestrial metamorphic adults which are exhibited by both sexes and which mate in the same aquatic habitat. Previous field studies on this species suggested that intermorph breeding would be less common during the winter months, because paedomorphic adults begin breeding in early autumn and thus may have less energy available for reproduction in the winter. Laboratory experiments conducted during the winter showed that the mating behavior of paedomorphic males occurred at a much lower frequency than that of metamorphic males. In contrast, field experiments that best mimicked natural conditions revealed symmetric intermorph breeding and included multiple paternity shared among males of each morph. This and other studies suggest that there is little evidence of sexual isolation among morphs based on behavioral interactions alone. However, the potential for partial isolation still occurs because of temporal and spatial differences in the frequencies of each morph in nature. Our results suggest that further studies on this system, and other similar polyphenisms, may provide valuable insight into the mechanisms that underlie the evolution of reproductive isolation.     

A population viability analysis for the Island Fox on Santa Catalina Island,California

The island fox (Urocyon littoralis) on Santa Catalina Island is among the most imperiled species on the Channel Islands due to a recent outbreak of canine distemper virus (CDV). The western subpopulation, which was not exposed to CDV, is a crucial element in the recovery of foxes by providing a source of animals for translocation and captive breeding. Using the program VORTEX, we developed a population viability analysis for the Santa Catalina Island fox to (1) address the likelihood of population persistence, (2) estimate the current susceptibility of the population to catastrophic events, and (3) evaluate the efficacy of current restoration strategies of releasing captive bred foxes and transplanting wild animals. Overall, we found the population to be susceptible to catastrophic events; a 50% increase in mortality every 20 years was sufficient to elevate the extinction risk above 5%. Current management activities entail the transplanting of 12 juvenile foxes annually, which may reduce the viability of the western subpopulation. A minimum population size of at least 150 foxes should be maintained in each subpopulation to reduce the risk of extinction due to demographic stochasticity. Releases of translocated and captive bred animals affect the speed of recovery on the eastern half of Catalina Island, but not the probability of extinction, which is near zero under current conditions. We conducted a sensitivity analysis for demographic parameters by incrementally varying survival, fecundity and density-dependence parameters, while holding all other parameters constant. Sensitivity analyses identified mortality and mean litter size as the most sensitive parameters, while the implementation of density-dependence and environmental variation of model parameters did not seem to affect population performance. We conclude that the population of island foxes on Santa Catalina is currently at a critically low population level, but recovery of the species appears possible.     

Avian Survival Rates and the Extinction Process on Barro Colorado Island, Panama

Abstract: Selective extinction following isolation of habitat patches may be due to biogeographical (e.g., island size or isolation) and ecological (species natural histories, interspecifc interactions) factors, or their interactions. Among the demographic and life history attributes commonly associated with high extinction probability are small populations, large size of individuals, and population variability. Long-term capture-recapture data from forest habitat in central Panama permit an examination of the association between mainland survival rates and extinction on a nearby land-bridge island Species of birds that no longer occur on Barro Colorado Island (BCI), Panama, have, on average, lower survival rates on the adjacent mainland than species that have persisted on BCI. Moreover, of the species that no longer occur on BCI, those with lower mainland survival rates generally disappeared earlier from the island. My analysis provides little evidence of a relationship between extinction and population size. Recolonization of BCI from the adjacent mainland by the forest undergrowth species studied here is unlikely. Reduced reproductive success on BCI combined with naturally low adult survival rates seems to be responsible for these BCI extinctions. High nest predation and/or altered landscape dynamics are probable agents in the low reproductive success. The methods used here could be employed in other circumstances to identify fragmentation-sensitive species.     

Life History as a Predictor of Salamander Recovery Rate from Timber Harvest in Southern Appalachian Forests,U.S.A

Forest management often represents a balance between social, economic, and ecological objectives. In the eastern United States, numerous studies have established that terrestrial salamander populations initially decline in abundance following timber harvest, yet the large‐scale and long‐term consequences are relatively unknown. We used count data from terrestrial survey points to examine the relation between salamander abundance and historic timber harvest while accounting for imperfect detection of individuals. Overall, stream‐ and terrestrial‐breeding salamanders appeared to differ by magnitude of population decline, rate of population recovery, and extent of recolonization from surrounding forest. Specifically, estimated abundance of both species groups was positively associated with stand age and recovery rates were predicted to increase over time for red‐legged salamanders (Plethodon shermani) and decrease in stream‐breeding species. Abundance of stream‐breeding salamanders was predicted to reach a peak by 100 years after timber harvest, and the population growth rate of red‐legged salamanders was predicted to undergo a significant increase 100 years after harvest. Estimated abundance of stream‐breeding salamanders in young forest stands was also negatively associated with the distance to adjacent forest, a result that suggests immigration has a role in the recovery of these species. Our results indicate that salamander abundance in young forest stands may be only modestly lower than in more mature forest but that full recovery from timber harvest may take a substantial amount of time and that species life history may affect patterns of recovery. Historia de Vida como un Vaticinador de la Tasa de Recuperación de una Salamandra a la Colecta de Madera en los Bosques del Sur de los Apalaches, E.U.A     

Calculating Biologically Accurate Mitigation Credits: Insights from the California Tiger Salamander

Abstract:  Current conservation mitigation plans often fail to ensure full in-kind habitat replacement for endangered species, which suggests the need for improved methods for calculating mitigation credits. A simple, yet biologically meaningful method for calculating mitigation credits would be to let the number of mitigation credits assigned to a parcel of land scale with the reproductive value of the individuals occupying that parcel. This can be accomplished by dividing the population into 2 or more subdivisions with different reproductive values, calculating the densities of these subdivisions as a function of one or more habitat parameters, and then forming a weighted sum of these densities such that each density distribution is weighted by the reproductive value of its respective subdivision of the population. This weighted sum is the density distribution of reproductive value, and by integrating it over a particular parcel, one can determine the mitigation value of that parcel. We carried out this procedure for a population of California tiger salamanders ( Ambystoma californiense ), with distance from breeding site as our habitat parameter and the 3 visually identifiable age classes (adults, juveniles, and metamorphs) as our population subdivisions. This led to a density distribution of reproductive value that decreased exponentially with increasing distance from a breeding site. Mitigation strategies derived from this function will be more likely to ensure the persistence of California tiger salamander populations than current approaches, which assign all land within 1.6 km of a breeding site the same mitigation value. Use of the density distribution of reproductive value as a basis for mitigation plans is a procedure that can be applied to all endangered species, and it should improve the quality of mitigation decisions.     

Reproductive success in a low skew, communal breeding mammal: the banded mongoose, Mungos mungo

In most cooperatively breeding species, reproduction is monopolised by a subset of group members. However, in some species most or all individuals breed. The factors that affect reproductive success in such species are vital to understanding why multiple females breed. A key issue is whether or not the presence of other breeders is costly to an individual’s reproductive success. This study examines the factors that affect the post-parturition component of reproductive success in groups of communal-breeding banded mongoose (Mungos mungo), where up to ten females breed together. Per-litter reproductive success was low (only 18% of pups survived from birth to independence). Whilst singular breeding was wholly unsuccessful, there were costs associated with breeding in the presence of increasing numbers of other females and in large groups. Synchronisation of parturition increased litter success, probably because it minimises the opportunity for infanticide or decreases competitive asymmetry between pups born to different females. There was no evidence of inbreeding depression, and reproductive success was generally higher in litters where females only had access to related males within their group. I conclude that communal breeding in female banded mongooses represents a compromise between the benefits of group-living and communal pup care on the one hand, and competition between females to maximise their personal reproductive success on the other. Such conflicts are likely to occur in most communal breeding species. Whilst communal breeding systems are generally considered egalitarian, negative effects of co-breeders on individual reproductive success is still an issue.     

Albatross populations in peril: a population trajectory for black-browed albatrosses at south Georgia.

Simulation modeling was used to reconstruct Black-browed Albatross (Diomedea melanophris) population trends. Close approximations to observed data were accomplished by annually varying survival rates, reproductive success, and probabilities of returning to breed given success in previous years. The temporal shift in annual values coincided with the start of longline fishing at South Georgia and potential changes in krill abundance. We used 23 years of demographic data from long-term studies of a breeding colony of this species at Bird Island, South Georgia, to validate our model. When we used annual parameter estimates for survival, reproductive success, and probabilities of returning to breed given success in previous years, our model trajectory closely followed the observed changes in breeding population size over time. Population growth rate was below replacement (lambda < 1) in most years and was most sensitive to changes in adult survival. This supports the recent IUCN uplisting of this species from "Vulnerable" to "Endangered." Comparison of pre-1988 and post-1988 demography (before and after the inception of a longline fishery in the breeding area) reveals a decrease in lambda from 0.963 to 0.910. A life table response experiment (LTRE) showed that this decline in lambda was caused mostly by declines in survival of adults. If 1988-1998 demographic rates are maintained, the model predicts a 98% chance of a population of fewer than 25 pairs within 78 years. For this population to recover to a status under which it could be "delisted," a 10% increase in survival of all age classes would be needed.     

Remarkable Amphibian Biomass and Abundance in an Isolated Wetland: Implications for Wetland Conservation

Abstract:  Despite the continuing loss of wetland habitats and associated declines in amphibian populations, attempts to translate wetland losses into measurable losses to ecosystems have been lacking. We estimated the potential productivity from the amphibian community that would be compromised by the loss of a single isolated wetland that has been protected from most industrial, agricultural, and urban impacts for the past 54 years. We used a continuous drift fence at Ellenton Bay, a 10-ha freshwater wetland on the Savannah River Site, near Aiken, South Carolina (U.S.A.), to sample all amphibians for 1 year following a prolonged drought. Despite intensive agricultural use of the land surrounding Ellenton Bay prior to 1951, we documented 24 species and remarkably high numbers and biomass of juvenile amphibians (>360,000 individuals; >1,400 kg) produced during one breeding season. Anurans (17 species) were more abundant than salamanders (7 species), comprising 96.4% of individual captures. Most (95.9%) of the amphibian biomass came from 232095 individuals of a single species of anuran (southern leopard frog [Rana sphenocephala ]). Our results revealed the resilience of an amphibian community to natural stressors and historical habitat alteration and the potential magnitude of biomass and energy transfer from isolated wetlands to surrounding terrestrial habitat. We attributed the postdrought success of amphibians to a combination of adult longevity (often >5 years), a reduction in predator abundance, and an abundance of larval food resources. Likewise, the increase of forest cover around Ellenton Bay from <20% in 1951 to >60% in 2001 probably contributed to the long-term persistence of amphibians at this site. Our findings provide an optimistic counterpoint to the issue of the global decline of biological diversity by demonstrating that conservation efforts can mitigate historical habitat degradation.     

Extinction, Colonization, and Metapopulations: Environmental Tracking by Rare Species

Extinction and metapopulation theories emphasize that stochastic fluctuations in local populations cause extinction and that local extinctions generate empty habitat patches that are then available for recolonization. Metapopulation persistence depends on the balance of extinction and colonization in a static environment. For many rare and declining species, I argue (1) that extinction is usually the deterministic consequence of the local environment becoming unsuitable (through habitat loss or modification, introduction of a predator, etc.); (2) that the local environment usually remains unsuitable following local extinction, so extinctions only rarely generate empty patches of suitable habitat; and (3) that colonization usually follows improvement of the local environment for a particular species (or long-distance transfer by humans). Thus, persistence depends predominantly on whether organisms are able to track the shifting spatial mosaic of suitable environmental conditions or on maintainance of good conditions locally.     

Bet hedging in a guild of desert annuals

Evolutionary bet hedging encapsulates the counterintuitive idea that organisms evolve traits that reduce short-term reproductive success in favor of longer-term risk reduction. It has been widely investigated theoretically, and many putative examples have been cited including practical ones such as the dormancy involved in microbe and weed persistence. However, long-term data on demographic variation from the actual evolutionarily relevant environments have been unavailable to test for its mechanistic relationship to alleged bet hedging traits. I report an association between delayed germination (a bet hedging trait) and risk using a 22-year data set on demographic variation for 10 species of desert annual plants. Species with greater variation in reproductive success (per capita survival from germination to reproduction x per capita fecundity of survivors) were found to have lower average germination fractions. This provides a definitive test using realistic data on demographic variance that confirms the life history prediction for bet hedging. I also showed that the species with greater long-term demographic variation tended to be the ones with greater sensitivity of reproductive success to variation among years in growing-season precipitation.     

Use of fecundity measured directly throughout the breeding season to test a source-sink demographic model

Populations of landbirds (bird species that occupy terrestrial habitats for most of their life cycle) are declining throughout North America (north of Mexico) and Europe, yet little is known about how demography is driving this trend. A recent model of 5 geographically separated populations of Cerulean Warblers (Dendroica cerulea) that was based on within-season sampling of nest survival and fledgling success shows that all populations are sinks (annual reproduction is consistently less than annual adult mortality). I tested this indirect model by directly measuring fecundity (number of female fledglings/female) during the breeding season for 2 years in a Cerulean Warbler population occupying a mature forest in southwestern Michigan (U.S.A.) I determined territories of male birds on the basis of male plumage characters and phases of the nesting cycle (2007) and on uniquely color-banded males (2008). I transferred locations of identified males to topographic maps. I counted all fledglings in territories from May to July each year. The model I tested may apply only to single-brooded species; therefore, I searched the literature to estimate the percentage of single-brooded species in North America. The breeding season of Cerulean Warblers was short- nearly all nests were initiated from mid-May to late June. Nest predation and brood parasitism were primary and rare causes of nest failure, respectively. Significantly fewer Cerulean Warblers fledged from parasitized than from nonparasitized nests. Fledgling survival required to maintain the population size was well above previously published values for Neotropical migrants. Single-brooded species comprise 62% of North American breeding bird species for which the number of broods per year is known; I believe my results may apply to these species. The consistency between identification of populations as sources or sinks on the basis of either model estimates or direct measurements suggests that a demographic model relying on within-season sampling of fecundity is adequate to determine population status of single-brooded avian populations. In addition, on the basis of results of previous studies, annual adult survival rate of the Cerulean Warbler is typical of parulid warblers that are not declining. Thus, low fecundity, here determined with different quantitative methods, can drive status of landbird species with high-observed survival.     

Role of Familiarity and Preference in Reproductive Success in Ex Situ Breeding Programs

Abstract: Success of captive‐breeding programs centers on consistent reproduction among captive animals. However, many individuals do not reproduce even when they are apparently healthy and presented with mates. Mate choice can affect multiple parameters of reproductive success, including mating success, offspring production, offspring survival, and offspring fecundity. We investigated the role of familiarity and preference on reproductive success of female Columbia Basin pygmy rabbits (Brachylagus idahoensis) as measured by litter production, litter size, average number of young that emerged from the burrow, and average number of young that survived to 1 year. We conducted these studies on pygmy rabbits at the Oregon Zoo (Portland, Oregon, U.S.A.) and Washington State University (Pullman, Washington, U.S.A.) from February to June 2006, 2007, and 2008. Before mating, we housed each female adjacent to 2 males (neighbors). Female preference for each potential mate was determined on the basis of behavioral interactions observed and measured between the rabbits. We compared reproductive success between females mated with neighbor and non‐neighbor males and between females mated with preferred and nonpreferred males. Our findings suggest that mating with a neighbor compared with a non‐neighbor and mating with a preferred neighbor compared with a nonpreferred neighbor increased reproductive success in female pygmy rabbits. Litter production, average number of young that emerged, and average number of young that survived to 1 year were higher in rabbits that were neighbors before mating than in animals who were not neighbors. Pairing rabbits with a preferred partner increased the probability of producing a litter and was significantly associated with increased litter size. In captive breeding programs, mates are traditionally selected on the basis of genetic parameters to minimize loss of genetic diversity and inbreeding coefficients. Our results suggest that integrating genetic information with social dynamics and behavioral measures of preference may increase the reproductive output of the pygmy rabbit captive‐breeding program. Our findings are consistent with the idea that allowing mate choice and familiarity increase the reproductive success of captive‐breeding programs for endangered species.     

The cost of success: reproductive effort in male southern elephant seals (<Emphasis Type="Italic">Mirounga leonina</Emphasis>)

Reproductive effort is a key parameter of life history because it measures the resources allocated to reproduction at the expense of growth and maintenance. Male reproductive effort always had a minor role with respect to female effort both in the development of theories and in field research. Elephant seals are an ideal subject for reproductive effort studies because they fast during the breeding season, splitting the phase of energy acquisition from the phase of energy use for breeding. In this paper, we present results on male reproductive effort (weight loss estimated by photogrammetry) in southern elephant seals (Mirounga leonina), the most dimorphic and polygynous of all mammal species. We show that total reproductive effort increases with age, with no sign of late decrease or senescence. Male reproductive effort in this species depends mostly on behavioral factors, i.e., the success in competition with other males, and the intensity of interaction with females. A large effort results in large gains in both mating success and fertilizations. The large reproductive success that a few males are able to achieve come at a big cost in terms of energy expenditure, but this cost does not seem to affect the likelihood of survival to the following breeding season.     

Do great tits rely on inadvertent social information from blue tits? A habitat selection experiment

Sympatric species sharing requirements are competitors, but recent evidence suggests that heterospecifics may also be used as a source of information. The heterospecific habitat copying hypothesis proposes that individuals of one species might use information inadvertently produced by the breeding performance of individuals of other species to assess habitat quality whenever the two species share needs. In this study, we provide the first experimental test of this hypothesis by examining whether the manipulated reproductive success of blue tits (Cyanistes caeruleus) is used as heterospecific inadvertent social information (ISI) in breeding-habitat selection by sympatric great tits (Parus major). The reproductive success of blue tits was manipulated 1year at the scale of patches by transferring nestlings from decreased to increased patches. No evidence was found of great tits using the reproductive success of blue tits as a source of heterospecific ISI. However, dispersal decisions by adult great tits correlated with information on con- and heterospecific densities, which constitute other sources of ISI. As density and breeding performance are tightly intertwined forms of information, the difficulty in distinguishing between them might lead great tits to use heterospecific ISI more in the form of density than breeding performance when making dispersal decisions.     

Estimation of Core Terrestrial Habitat for Stream-Breeding Salamanders and Delineation of Riparian Buffers for Protection of Biodiversity

Abstract:  Many species of wildlife depend on riparian habitats for various life-history functions (e.g., breeding, foraging, overwintering). Although this unique habitat is critical for many species, delineations of riparian zones and buffers for various taxa are lacking. Typically when buffer zones are determined to mitigate edge effects, they are based on criteria that protect aquatic resources alone and do not consider impacts to wildlife and other terrestrial resources. Using two different survey methods (area-constrained daytime searches and nighttime visual encounter searches), we estimated core terrestrial habitat and buffer widths for stream-breeding salamanders in southern Appalachian streams from May to August 2004. A core terrestrial habitat of 27.0 m encompassed 95% of the salamander assemblage (four species of stream plethodontids), and an additional 50 m (to buffer edge effects) yielded a total buffer of 77.0 m. When each species of the assemblage was analyzed separately, the maximum core terrestrial habitat needed for the Blue Ridge two-lined salamander ( Eurycea wilderae ), a dominant member and the farthest-ranging species from the stream, was 42.6 m. Thus, we recommend an overall buffer width of 92.6 m in southern Appalachian streams. To protect stream amphibians and other wildlife dependent on riparian areas, land managers and policy makers must consider conserving more than aquatic resources alone. Developing core terrestrial habitat estimates and buffer zone widths for wildlife populations is a critical first step in the conservation of many semiaquatic organisms and protecting biodiversity.     

The effects of helpers in cooperatively breeding purple gallinules

Summary The effects of helpers in a population of cooperatively breeding purple gallinules (Porphyrula martinica) were examined. All young birds past the age of 2 months helped feed and protect subsequent broods of chicks and participated in territorial defense. Most helpers remained on their natal territories for approximately 1 year. The number of helpers varied both among and within breeding groups. Clutch production and chick survival were related positively to the number of helpers in the group. The increase in chick survival was independent of several measures of territory quality. Helpers possibly aided chick survival by provicing extra food for the chicks and decreasing predation risk. Helpers were necessary in order for a breeding pair to keep a territory long enough to produce more than one clutch of eggs. A change in the number of helpers (increase or decrease) often was followed by a similar change in territory size. These results suggest that purple gallnule helpers can increase the reproductive success of the breeding group and may be vital for the continued maintenance of a breeding territory.