Phalcoboenus Australis Research Articles

Long-term memory in wild falcons

Long-term memory - information retention over long timescales - can allow animals to retain foraging skills and efficiently respond to seasonally available resources and changing environments1. Most long-term memory research is with captive species, focusing on spatial, individual or object recognition, with less known about wild species and the retention of motor task abilities, as in the case of complex foraging skills2,3. We have examined whether wild striated caracaras (Phalcoboenus australis), recently shown to rapidly and flexibly innovate with an eight-task puzzle box4, retain task memories one year later. We found that, despite no reinforcement, caracaras repeated motor techniques that led to their most recent success on tasks the year prior, solving nearly twice as fast as a naïve control group and four times faster than when naïve. Our results suggest long-term memory may be important for non-migratory opportunistic generalists, particularly in remote island environments with seasonally available resources, and further highlight how striated caracaras are promising candidates for avian cognitive studies.

Assessing Knowledge of the Caracaras: Compiling Information, Identifying Knowledge Gaps, and Recommendations for Future Research

ABSTRACT Because information availability and management are essential components of wildlife conservation, we sought to compile literature published since 1900 on the caracaras, a group of nine extant species, eight of which occur only in Central America and South America. Our findings revealed that the number of sources and therefore, the amount and types of information available varied considerably among the caracara species and among countries where these raptors occur. Most sources represented studies conducted in Argentina, the United States, Brazil, and Chile, and many focused on the more common species, for example, the Crested Caracara (Caracara plancus) and the Chimango Caracara (Milvago chimango). Most sources published in the early 20th century focused on breeding and feeding ecology and natural history. Since the 1960s, the number of studies published per decade has increased, and since the 1990s, more studies have addressed a broader range of topics including behavioral ecology, demography, infectious agents, parasites, contaminants, biomedicine, and taxonomic relatedness among the caracara species and other falcons. Aside from the Striated Caracara (Phalcoboenus australis), which recently has been the subject of intensive research, other species in the genus Phalcoboenus (the Mountain Caracara [P. megalopterus]; the White-throated Caracara [P. albogularis]; and the Carunculated Caracara, [P. carunculatus]) remain little known, as do the two forest-dwelling caracaras, the Black Caracara (Daptrius ater) and the Red-throated Caracara (Ibycter americanus). Knowledge gaps exist for all the caracaras; research is especially needed on subjects outside typically studied topics such as breeding and feeding ecology. Also important to expanding knowledge of this group will be collaboration with researchers studying other avian scavengers such as condors and vultures, focusing on common threats, and coordination among researchers in countries inhabited by multiple caracara species.

Innovative problem solving by wild falcons

Innovation (i.e., a new solution to a familiar problem, or applying an existing behavior to a novel problem1,2) plays a fundamental role in species' ecology and evolution. It can be a useful measure for cross-group comparisons of behavioral and cognitive flexibility and a proxy for general intelligence.3,4,5 Among birds, experimental studies of innovation (and cognition more generally) are largely from captive corvids and parrots,6,7,8,9,10,11,12 though we lack serious models for avian technical intelligence outside these taxa. Striated caracaras (Phalcoboenus australis) are Falconiformes, sister clade to parrots and passerines,13,14,15 and those endemic to the Falkland Islands (Malvinas) show curiosity and neophilia similar to notoriously neophilic kea parrots16,17 and face similar socio-ecological pressures to corvids and parrots.18,19 We tested wild striated caracaras as a new avian model for technical cognition and innovation using a field-applicable 8-task comparative paradigm (adapted from Rössler et al.20and Auersperg etal.21). The setup allowed us to assess behavior, rate, and flexibility of problem solving over repeated exposure in a natural setting. Like other generalist species with low neophobia,21,22 we predicted caracaras to demonstrate a haptic approach to solving tasks, flexibly switching to new, unsolved problems and improving their performance over time. Striated caracaras performed comparably to tool-using parrots,20 nearly reaching ceiling levels of innovation in few trials, repeatedly and flexibly solving tasks, and rapidly learning. We attribute our findings to the birds' ecology, including geographic restriction, resource unpredictability, and opportunistic generalism,23,24,25 and encourage future work investigating their cognitive abilities in the wild. VIDEO ABSTRACT.

Variation in nest‐site occupancy and breeding outcome in a threatened Subantarctic raptor

Breeding outcome in birds can be influenced by both intrinsic and extrinsic factors, which may contribute differentially to each stage of the breeding cycle. Island raptors are relatively threatened species that rely on simplified food webs and usually co‐occur with invasive species. Here, we studied a population of Striated Caracara Phalcoboenus australis in Isla de los Estados (Argentina) to understand the relative contribution of food availability, topographical features and territoriality to breeding parameters. Caracaras in the area depend on the short seasonal (i.e. pulsed) availability of seabirds for feeding their chicks. On the other hand, the recent introduction of non‐native ungulates may have led to a suboptimal breeding environment by reducing Caracara nest‐site availability within the seabird colonies via disturbance of the grassland. Using data from seven breeding seasons we analyse the abundance, the proportion of breeding individuals, the spatial structure of breeding events and the population‐level breeding performance, including chick sex ratio, to study whether the breeding ecology of this species is still shaped by marine food web pulses or could be associated with invasive herbivore disturbance. The breeding adults represented only 6–15% of the population. The spatial pattern of nest‐sites did not differ from random arrangement after considering the heterogeneous distribution of food availability. Territory identity accounted for most of the variation in clutch size and productivity, and penguin availability explained part of the variability in territory occupancy and hatching rate. The chick sex ratio was biased towards females and varied according to brood size, with the more productive territories producing 91% of males. The breeding cycle of this population is still mainly dependent upon the Rockhopper Penguin Eudyptes chrysocome food pulse and presents mixed evidence of being disrupted by invasive herbivores. The studied factors contributed differentially to the output of each reproductive stage, with territory identity accounting for most of the variation. Our results suggest that individual‐level, long‐term data could be relevant to understanding the dynamics of this species in the Fuegian archipelago, and thus a broad‐scale research programme is warranted to assess the conservation status and propose future management scenarios for this species.

Status of breeding birds at Observatorio and Goffré Islands, Argentina

Continental islands are often sites of low diversity and endemism, as well as important areas for the protection of bird populations, especially seabirds. On Isla Observatorio and the Año Nuevo Islands, in the Southwestern Atlantic, the latest assessment of avifauna dates from more than 20 years ago. In this study, we use a combination of methods to update the status of the main seabird colonies and the most abundant avian terrestrial predator at Observatorio and Goffré Islands during the breeding season. In only 4.5 km2, the islands would harbour ~ 90,000 breeding seabirds. Seabird colonies occupied different areas of the islands and varied in their population status, with Imperial Shags (Leucocarbo atriceps) showing an increase and Southern Giant Petrels (Macronectes giganteus) a decrease according to the last surveys. Magellanic Penguin (Spheniscus magellanicus) population estimations also suggest a decrease but the last survey was based on total, and not on occupied nest sites. We recorded and assessed one new breeding species: The globally near-threatened Striated Caracara (Phalcoboenus australis), which has an important breeding population of around 15 territorial pairs at Observatorio Island. These islands appear to be an important regional bird site and future studies would determine their trends and threats, especially those related with invasive species.

Use of appeasement display and recruitment by an adult Striated Caracara (Phalcoboenus australis) to overcome territorial defense

Adult animals across many taxa use appeasement signaling to minimize or avoid costly conflict in social settings by jointly communicating their consent to defer and an interest to remain. When foraging, however, appeasement may not be enough to gain access to a resource controlled by a dominant conspecific. In this case, conspecific recruitment can shift the social dynamic, so the resource becomes accessible to all. Striated Caracara (Phalcoboenus australis) are Near Threatened scavenging falconids that breed in high densities on the extreme southern coasts of South America and the Falkland Islands. While juvenile caracaras recruit other caracaras to concentrated food resources, neither recruitment nor appeasement has been reported in adults. Here we describe a female adult caracara that appeared to use both appeasement signaling and recruitment to access food in another pair's defended territory on New Island, Falkland Islands. Appeasement and recruitment calls are one of several behavioral parallels that researchers have noted among Striated Caracara, Common Raven (Corvus corax), and Kea (Nestor notabilis). Although falconids are not typically considered in comparative studies of avian cognition and social behavior, we suggest that caracaras merit further attention, especially given their relationship to parrots in the clade Eufalconimorphae.

The highest mercury concentrations ever reported in a South American bird, the Striated Caracara (Phalcoboenus australis)

Mercury is a widely available pollutant associated with negative effects on wildlife, especially top predators. Here, we characterized the mercury concentrations in feathers of Striated Caracara Phalcoboenus australis on Isla de los Estados (Argentina). With feather mercury levels averaging 26.3 mg/kg, this population has the highest mean feather mercury ever reported for a bird population in South America. We propose that the high mercury concentrations are related to the feeding habits of the species: during feather moult, they are strongly associated with a Southern Rockhopper Penguin (Eudyptes chrysocome) colony known to be highly exposed to mercury contamination. Our results suggest that this Striated Caracara population should be monitored for acute effects and potential impacts of mercury toxicity.

The highest mercury concentrations ever reported in a South American bird, the Striated Caracara (Phalcoboenus australis)

The highest mercury concentrations ever reported in a South American bird, the Striated Caracara (Phalcoboenus australis)

Winter bird gets the worm: consumption of earthworms (Lumbricidae) by striated caracaras (Phalcoboenus australis) in invasive Yorkshire fog (Holcus lanatus) in the Falkland Islands (Malvinas)

Biological invasions can drive ecosystem change and alter predator ecology by providing trophic subsidies that mitigate the effects of seasonally pulsed resources. Striated Caracaras (Phalcoboenus australis) are near threatened, non-migratory falconids who inhabit the southern coasts of South America and the Falkland Islands (Malvinas) and feed on seasonally migratory colonial seabirds. Here we report the first multi-day observation of caracaras foraging extensively for earthworms (Lumbricidae) and beetle larvae (Coleoptera) in introduced Yorkshire fog (Holcus lanatus) on New Island, Falkland Islands. Our results suggest that invertebrates may be a more important winter resource than previously thought, and that caracaras benefit indirectly from introduced grasses in the Falklands, a relationship that merits special consideration when identifying ecological restoration plans.

The dynamic trophic niche of an island bird of prey.

Optimal foraging theory predicts an inverse relationship between the availability of preferred prey and niche width in animals. Moreover, when individuals within a population have identical prey preferences and preferred prey is scarce, a nested pattern of trophic niche is expected if opportunistic and selective individuals can be identified. Here, we examined intraspecific variation in the trophic niche of a resident population of striated caracara (Phalcoboenus australis) on Isla de los Estados (Staten Island), Argentina, using pellet and stable isotope analyses. While this raptor specializes on seabird prey, we assessed this population's potential to forage on terrestrial prey, especially invasive herbivores as carrion, when seabirds are less accessible. We found that the isotopic niche of this species varies with season, age, breeding status, and, to a lesser extent, year. Our results were in general consistent with classic predictions of the optimal foraging theory, but we also explore other possible explanations for the observed pattern. Isotopic niche was broader for groups identified a priori as opportunistic (i.e., nonbreeding adults during the breeding season and the whole population during the nonbreeding season) than it was for individuals identified a priori as selective. Results suggested that terrestrial input was relatively low, and invasive mammals accounted for no more than 5% of the input. The seasonal pulse of rockhopper penguins likely interacts with caracara's reproductive status by constraining the spatial scale on which individuals forage. Niche expansion in spatially flexible individuals did not reflect an increase in terrestrial prey input; rather, it may be driven by a greater variation in the types of marine prey items consumed.

Seasonal activity levels of a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands

BackgroundAnimals need adaptive strategies to cope with seasonal changes in prey availability to survive and reproduce, which can include migrating, prey-switching, or reducing metabolic needs. Human settlements can disrupt spatiotemporal patterning in resource availability, which can affect animals’ foraging success, particularly for juveniles who are behaviorally developing and learning efficient foraging skills. Here, we investigate behavioral responses of juvenile striated caracaras, a near-threatened scavenging falconid, to seasonally migratory seabird prey and a farm settlement on Saunders Island, Falklands. We deployed accelerometer–GPS dataloggers (n = 27) to measure seasonal differences in daily and hourly vectorial dynamic body acceleration (VeDBA; an activity index measured in gravitational g) and space use, and investigated seasonal variation in body mass of the tagged subset and an additional 65 caracaras.ResultsJuvenile caracaras were overall similarly active in winter and summer. However, during winter, caracaras made the most of limited daylight by increasing average daytime activity (winter males: 0.16 ± 0.03 g, summer males: 0.09 ± 0.01 g, winter females: 0.12 ± 0.02 g, summer females: 0.08 ± 0.01 g). During winter, both sexes increased the percentage of daylight spent in high activity (winter males: 35 ± 5%, summer males: 21 ± 3%, winter females: 25 ± 6%, summer females: 16 ± 3%, p < 0.001) and ranged nearly 4 times farther (95% kernel density estimate winter: 2.36 ± 0.96 km2, summer: 0.61 ± 0.20 km2; p < 0.001). Furthermore, on a daily scale, males were 21% more active than females year-round (24-h average VeDBA: males 0.07 ± 0.01 g, females 0.06 ± 0.01 g; p < 0.01). We did not observe a significant seasonal difference in mass.ConclusionThat caracaras’ daily activity and body mass did not vary between seasons suggests that wintering birds on Saunders are meeting resource requirements despite the absence of seasonally migratory prey. We hypothesize that human subsidies may mitigate the effect of seasonal food limitations. Further research should include studies on seasonal energetics to improve our understanding of baseline body condition, and comparative studies on other islands and including adults to understand the importance of human subsidies.

Predation of Southern Red Octopus (Enteroctopus megalocyathus) by Striated Caracaras (Phalcoboenus australis) in the Falkland Islands

Predation of Southern Red Octopus (Enteroctopus megalocyathus) by Striated Caracaras (Phalcoboenus australis) in the Falkland Islands

Social scavenging by wintering striated caracaras (Phalcoboenus australis) in the Falkland Islands

Avian scavengers perform vital ecosystem services by removing waste and slowing disease, yet few details are known about the process of carcass depletion, or the role of social interactions among groups of scavengers. The striated caracara (Phalcoboenus australis) is a social scavenging falconid of the Falkland Islands, whose boldness and reliance on human settlements as winter foraging grounds make it an ideal species with which to closely examine carcass use over the entire period of a carcass’ availability. By providing and monitoring experimental carcasses, we estimated the mass of food consumed per individual during 5-min intervals and compared the rate of group formation in the presence and absence of conspecific vocalizations. We found (1) that food obtained per individual was greater toward the beginning of carcass availability, when competition was fierce; (2) that vocalizations, by birds at and approaching the carcass, preceded periods of faster group formation; and (3) that on average birds would approach a speaker playing conspecific calls more closely than one playing a control recording. Our observations add to those of social foraging in other scavengers, providing a study of carcass use and vocalization at these ephemeral resources. Currently ranked as Near Threatened by BirdLife International, the remote and restricted range of the striated caracara (Phalcoboenus australis) has made it a difficult study subject, though conservation concerns show it warrants deeper research. A social scavenging falconid of the Falkland Islands, striated caracaras have been persecuted as livestock pests since the 1800s, but their reliance on human settlements as winter foraging grounds makes them an ideal species with which to examine social scavenging behavior. This study was undertaken to investigate group feeding at carcasses by striated caracaras in austral winter, and to better understand the social function of their vocalizations. Furthering our knowledge of avian vocalizations is essential to certain wildlife management strategies, and empirically testing the effects of playbacks on target species is a crucial prior step to the use of any bio-acoustic tool.

Distribution and Abundance of Breeding Striated Caracaras in the Falkland Islands (Malvinas)

We conducted surveys of breeding pairs of the endemic and globally “Near Threatened” Striated Caracara (Phalcoboenus australis) on 79 outer islands in the Falklands archipelago (Islas Malvinas) during the austral-summer breeding seasons of 2013–2014 and 2014–2015. A total of 354 breeding pairs (defined as pairs with evidence of egg-laying), or an archipelago-wide adult breeding population of at least 0.05 birds/km2 was recorded. An additional 477 probable breeding pairs also were found. The distribution of breeding pairs remains similar to that found during surveys in the 1990s and 2000s. Grand Jason, Steeple Jason, New Island, Beauchene Island, and Bird Island, the five islands with the highest numbers of breeding pairs, accounted for half of the total breeding population. “Vegetationally pristine” islands with dense areas of tussac grass (Poa flabellata) and high densities of small burrowing seabirds—namely Bird Island, Saddle Island, and Beauchene Island—supported the highest densities of breeding pairs. Eighty percent of all pairs occurred on National Nature Reserves or on privately owned nature sanctuaries. Our surveys suggest that sustained protection of key breeding sites is critical for the long-term conservation of this species. We recommend that populations of Striated Caracaras at Tierra del Fuego also be surveyed and that the global population status of the species be reassessed.

Seasonal micro-migration in a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands

BackgroundThe extent to which seasonal changes in food availability affect small-scale movements in free-ranging populations of birds of prey is relatively little studied. Here we describe a seasonal “micro-migration” of a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands in response to seasonal changes in the availability of seabird carcasses. We banded more than 450 individuals on Saunders Island, deployed archival and satellite GPS data loggers on 17 individuals, and monitored movements within and between two feeding areas on Saunders Island, a “marine-subsidized” site near seabird colonies and an anthropogenic “human-subsidized” farm site 16 km to the southeast.ResultsDuring 67 observation days between 2010 and 2015, resightings of 312 banded caracaras were greater at the marine-subsidized site during austral summer than winter, and the total daily resightings varied significantly between spring versus summer, summer versus winter, autumn versus spring, and autumn versus winter. Resightings were higher at the human-subsidized site in austral winter than summer and the total daily resightings varied significantly across all bi-seasonal comparisons. Resightings indicated that at least 12 of 197 birds (6.1%) moved between the human- and marine-subsidized sites at least once during the same winter, 15 of 335 birds (4.5%) did so in spring, none of 164 birds did so in summer, and 16 of 297 birds (5.4%) did so in autumn. Individuals fitted with archival GPS data loggers at the marine-subsidized site in summer maintained highly localized 95% kernel core areas (0.55 ± 0.12 km2 [mean ± SD]), whereas those at the human-subsidized site in winter maintained larger 95% kernel core areas (3.8 ± 4.6 km2). Two of 6 satellite-tagged individuals that summered at known caracara breeding colonies 80 km WNW of Saunders Island were subsequently resighted in winter at the human-subsidized site.ConclusionOur results suggest that seasonal shifts in food resource availability drive seasonal micro-migrations in a farm-island population of striated caracaras, and that farm sites can be critical in providing nutritional resources for caracaras when naturally occurring marine-subsidized resources become less available. Our results have important implications for striated caracara spatial ecology and conservation, as increased winter survival could improve the status of this globally Near-Threatened population.

Status and Reproductive Outcome of the Breeding Population of Striated Caracaras (Phalcoboenus australis) at Franklin Bay, Staten Island, Argentina

ABSTRACT.— The Striated Caracara (Phalcoboenus australis) is a poorly known raptor associated with seabird colonies, restricted to the islands of southern South America, and with an estimated extant population of <2,500 mature individuals. We evaluated the number of breeding pairs, described the characteristics and spatial pattern of nest sites, and estimated breeding output of a population of Striated Caracaras in Franklin Bay, Staten Island, Argentina. We found one of the lower breeding density values reported for this species, although this population is associated with one of the biggest colonies of Rockhopper Penguins. The main material used for the construction of Striated Caracaras' nests was tussac grass, though only half of nests were placed in grassland. The spatial pattern for nest sites corresponds with global and local clustering. All successful Striated Caracaras' nests were at least 250 m from the nearest neighboring nest, were generally closer to the colony of Rockhopper Penguins than fail...

Observations Suggesting Cooperative Breeding by Striated Caracaras (Phalcoboenus australis)

Observations Suggesting Cooperative Breeding by Striated Caracaras (<i>Phalcoboenus australis</i>)

Winter diet of striated caracara Phalcoboenus australis (Aves, Polyborinae) at a farm settlement on the Falkland Islands

Striated caracaras occur only on the Falkland Islands and the outer islands of southern Chile and Argentina. In summer, the species associates with seabirds and seals and depends heavily upon them for food. The winter diet is less well understood. We studied the diet of 90–130 mainly juvenile and sub-adult striated caracaras overwintering at a farm on Saunders Island, Falkland Islands, in mid-winter (July–August) 2011. Direct observations of feeding and regurgitation pellets collected at a roost indicate that the winter diet of the striated caracaras at the site is mainly native geese, beetles and other invertebrates, and the carcasses of domestic sheep. This study illustrates seasonal shifts in the diet of this near-threatened South Atlantic endemic and suggests an important nutritional link between juvenile and subadult caracara survival in winter and traditional human activities at sheep farms.

Social Hierarchy of Scavenging Raptors on the Falkland Islands, Malvinas

On the Falkland Islands (Malvinas), raptors historically were perceived as a threat to livestock, and consequently were widely persecuted through the mid-twentieth century. Conservation measures now minimize persecution and have facilitated increases in raptor populations, but the ecology of raptors on the Falkland Islands (Malvinas) remains poorly understood. We investigated social hierarchies within an assemblage of nonmigratory raptorial scavengers: Variable Hawk (Buteo polyosoma), Striated Caracara (Phalcoboenus australis), Southern Caracara (Caracara plancus), and Turkey Vulture (Cathartes aura jota). During thirty observation sessions of 30 min each, we recorded 1386 aggressive interactions involving one or more of these species. We found that Variable Hawks were aggressors in 98% (95% CI = 96–100%) of interactions with Striated Caracaras, 82% (69–95%) of interactions with Turkey Vultures, and 80% (72–88%) of interactions with Southern Caracaras. Southern Caracaras were aggressors in 100% of interactions with Striated Caracaras, and 90% (80–100%) of interactions with Turkey Vultures. Turkey Vultures were aggressors in 71% (61–82%) of interactions with Striated Caracaras. Within species, we found adult Southern Caracaras were aggressors in 78% (72–84%) of interactions with conspecific juveniles and 76% (68–85%) of interactions with conspecfic subadults. Adult Striated Caracaras were aggessors in 100% of interactions with conspecific juveniles and 97% (91–100%) of interactions with conspecfic subadults. Predicted patterns of size-based dominance typical of complex African and South American avian scavenger assemblages were not observed in the relatively simple assemblage of the Falkland Islands (Malvinas), but we did observe single-species groups of up to 83 Southern Caracaras and 42 Striated Caracaras.

Population growth and density, diet and breeding success of striated caracaras Phalcoboenus australis on New Island, Falkland Islands

The striated caracara is a rare and specialised raptor, with a distribution restricted to outer islands of southern South America and the Falklands, where it lives in a unique obligate association with seabirds and seals. Despite its tameness, interesting adaptations and the fact that it is classified as near-threatened, there is virtually no published quantitative information on its demography, ecology and behaviour. We carried out a study on New Island, West Falklands, where the species was eradicated due to heavy persecution up to the 1960s. Recolonisation started after 1972 and presently there are an estimated 85 adult territorial pairs plus ca. 130 non-territorial immatures, representing an overall density of 15.5 striated caracaras per km2. The population is estimated to have increased by 15% per year over the past 3 decades, with the result that New Island now harbours the largest known breeding aggregation on a single island in the entire breeding range of the species. The spring and summer diet of striated caracaras on New Island is dominated by one small seabird, the thin-billed prion Pachyptila belcheri. An estimated 25,000 adult and sub-adult prions are consumed every year, but this possibly represents less than 1% of the local population. The diet of different pairs displayed significant differences, which were probably related to differences in the availability of prey types between territories. Breeding success in recent years was very high, suggesting that conditions are good and the population may not yet have reached the island’s carrying capacity.