Despite empirical and experimental work in a variety of taxa, a general understanding of investment strategies in cooperative breeders has proven difficult. Analysis of provisioning patterns in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus) reveals that whether birds reduce their investment when assisted by other individuals depends on the analytical approach, including the type of data used as an index of effort and the time span over which it is measured. Estimated by group composition over the course of a complete nesting effort, provisioning is compensatory, with birds reducing their feeding rates in larger groups. In contrast, when measured by the provisioning effort of other group members on a short-term, individual watch basis, provisioning is additive, with birds matching the feeding rates of other group members. Both the time frame over which patterns of parental and parental-like care are made and the type of data used need to be considered to understand investment strategies by individuals in social groups.

Theory predicts that high population density leads to more strongly connected spatial and social networks, but how local density drives individuals' positions within their networks is unclear. This gap reduces our ability to understand and predict density-dependent processes. Here we show that density drives greater network connectedness at the scale of individuals within wild animal populations. Across 36 datasets of spatial and social behaviour in >58,000 individual animals, spanning 30 species of fish, reptiles, birds, mammals and insects, 80% of systems exhibit strong positive relationships between local density and network centrality. However, >80% of relationships are nonlinear and 75% are shallower at higher values, indicating saturating trends that probably emerge as a result of demographic and behavioural processes that counteract density's effects. These are stronger and less saturating in spatial compared with social networks, as individuals become disproportionately spatially connected rather than socially connected at higher densities. Consequently, ecological processes that depend on spatial connections are probably more density dependent than those involving social interactions. These findings suggest fundamental scaling rules governing animal social dynamics, which could help to predict network structures in novel systems.

Walt Koenig and colleagues introduce the acorn woodpecker, a cooperatively breeding, food-caching bird of North America.

Long-term studies are subject to stochastic forces as well as deterministic, ecological differences. We illustrate this by means of Polya’s urn scheme and two examples based on our long-term study of the behavioral ecology of the acorn woodpecker (Melanerpes formicivorus). In both cases, the years during which the study was conducted had a large, apparently stochastic influence on population dynamics. Despite such variability, long-term studies offer several notable benefits, including the opportunity to gain a more nuanced understanding of a particular system and the ability to incorporate technological and theoretical advances. Ultimately, it is with long-term data that we can hope to disentangle and understand the stochastic and deterministic factors that drive ecological systems.

Avian communities composed of a total of 79 species were sampled repeatedly at different times of day throughout the breeding season in Norfolk, Virginia, USA. Estimates of taxonomic diversity (species richness, Shannon index and probability of interspecific encounter) were highest in the morning, whereas estimates of functional diversity (functional richness, evenness, Rao's entropy and mean distinctiveness) did not vary significantly throughout the day. These results suggest that estimates of taxonomic diversity in avian communities are biased by time-of-day, but measures of functional diversity may be more robust to such bias.

Dispersal limitation and variation in habitat suitability may determine an association of American mistletoe [Phoradendron leucarpum (Raf.) Reveal & M.C. Johnst. (Viscaceae)] with forested wetlands in Virginia and North Carolina, United States. Here, we first tested the alternative hypothesis that variation in host availability drives this habitat relationship. We used a generalized linear model to show a positive effect of forested wetland habitat on American mistletoe occurrence after accounting for both variation in host availability and differences among regions in host use. We then used seed sowing experiments to quantify how light availability and flood regime determine the viability of American mistletoe, allowing us to evaluate the potential for establishment limitation to determine this habitat relationship. Light availability predicted establishment rates but % canopy openness did not predict seed germination rates. Thus, variation in the ability for American mistletoe to establish across forested habitat types with different local light availabilities is a potentially important mechanism in determining its distribution.

High population density should drive individuals to more frequently share space and interact, producing better-connected spatial and social networks. Despite this widely-held assumption, it remains unconfirmed how local density generally drives individuals' positions within wild animal networks. We analysed 34 datasets of simultaneous spatial and social behaviour in >55,000 individual animals, spanning 28 species of fish, reptiles, birds, mammals, and insects. >80% of systems exhibited strongly positive relationships between local density and network centrality, providing broad empirical evidence that local density increases connectedness at the individual level. However, >75% of density-connectedness relationships were nonlinear, and density's importance declined at higher values in >70% of systems, signifying saturating effects. Density's effect was much stronger and less saturating for spatial than social networks, suggesting population density drives individuals to become disproportionately spatially connected rather than socially. These findings reveal fundamental trends underlying societal structuring, with widespread behavioural, ecological, and evolutionary implications. ### Competing Interest Statement The authors have declared no competing interest.

Offspring that delay dispersal in cooperatively breeding species have been hypothesized to gain direct fitness benefits via parental facilitation-being passively tolerated on their natal territory by their parents-thereby enjoying enhanced survival and increased probability of acquiring a breeding position in the population. Here we describe active facilitation in the acorn woodpecker (Melanerpes formicivorus) by parents and siblings assisting the dispersal of helpers in their social group. Helpers in this species compete for reproductive opportunities in "power struggles" that take place when all breeders of one sex die or disappear, creating a reproductive vacancy. Individuals compete at power struggles in coalitions of relatives, in which larger coalitions are more likely to be victorious. Based on observations of banded birds, we found that an estimated 26% of individuals competing as part of a winning coalition at a power struggle returned to their home territory at its conclusion, suggesting that they were facilitating the dispersal of kin (generally parents or siblings) that stayed to become breeders on the new territory. In at least one group, sibling facilitation was reciprocated; that is, a bird that was helped at a power struggle by a sibling joined that same sibling as part of a coalition at a subsequent power struggle. Dispersal facilitation is a novel means by which parents can nepotistically enhance the direct fitness of offspring and siblings can enhance each other's inclusive fitness in this highly social species. Significance statement Parental facilitation-being passively tolerated on the natal territory-may provide significant direct fitness benefits to helpers in cooperatively breeding species. We describe active facilitation of helper dispersal in the acorn woodpecker, where helpers compete in coalitions for reproductive opportunities at "power struggles" following the death or disappearance of all breeders of one sex. About one-fourth of individuals-including both parents and siblings-competing at power struggles were apparently facilitators who assisted related helpers by participating in the power struggle but then returned to their home territory rather than stay to breed on the new territory. In at least one group, dispersal facilitation was reciprocated; that is, a bird that was helped at a power struggle by a relative later joined that same relative as part of a coalition at a subsequent power struggle. Active dispersal facilitation by parents and siblings is an important, previously unrecognized, form of nepotistic behavior in this highly social species.

Context Spatial occupancy and local abundance of species often positively covary, but the mechanisms driving this widespread relationship are poorly understood. Resource dynamics and habitat changes have been suggested as potential drivers, but long-term studies relating them to abundance and occupancy are rare. In this 34-year study of acorn woodpeckers ( Melanerpes formicivorus ), a cooperatively breeding species, we observed a paradoxical response to changes in habitat composition: despite a reduction in the availability of high-quality breeding habitat, the population increased considerably. Objectives We investigated the role of annual variation in food availability and long-term changes in habitat composition as predictors of population dynamics. Methods Using model selection, we contrasted competing hypotheses on the effects of changing resource availability on occupancy and social group size across three spatial scales: territory, neighborhood, and landscape. Results The increase in abundance was largely determined by the formation of new social groups, driven by a landscape-level expansion of canopy cover and its interaction with neighborhood-level acorn abundance, indicative of long-term increases in overall acorn productivity. Group size increased with neighborhood acorn crop two years earlier but groups were smaller in territories with more canopy cover. Conclusions Our results indicate that scale-dependent processes can result in paradoxical relationships in systems with spatial and temporal resource heterogeneity. Moreover, the findings support the role of resources in driving changes in abundance and occupancy at a landscape scale, suggesting that colonization of marginal habitat drives the positive occupancy-abundance relationship in this cooperatively breeding species.

Climate change has contributed to increased wildfires1,2. Wildfire smoke exposes wildlife to hazards and mortality from particulate matter on a scale larger than the area impacted by fire3,4. Using automated radiotelemetry, we illustrate how smoky conditions are associated with changes in behavior of acorn woodpeckers (Melanerpes formicivorus), a flagship species of oak (Quercus spp.) savannas of western North America. On smoky days, birds spent more time at their home territory and reduced visitation to others, especially to distant territories. Associations between birds decreased, and individuals were less assorted by group in co-visitation networks, suggesting less inter-individual coordination on smoky days. We show that between 2016 and 2020, ∼14% of the acorn woodpecker population in the US experienced fire, potentially exposing on average 89.42% of the range to atmospheric smoke annually. These findings highlight how potential effects of smoke on animal behavior may be widespread and exacerbate negative impacts of increasingly common "megafires", even in fire-adapted ecosystems.

Although over 50 y have passed since W. D. Hamilton articulated kin selection and inclusive fitness as evolutionary explanations for altruistic behavior, quantifying inclusive fitness continues to be challenging. Here, using 30 y of data and two alternative methods, we outline an approach to measure lifetime inclusive fitness effects of cooperative polygamy (mate-sharing or cobreeding) in the cooperatively breeding acorn woodpecker Melanerpes formicivorus. For both sexes, the number of offspring (observed direct fitness) declined while the number of young parented by related cobreeders (observed indirect fitness effect) increased with cobreeding coalition size. Combining these two factors, the observed inclusive fitness effect of cobreeding was greater than breeding singly for males, while the pattern for females depended on whether fitness was age-weighted, as females breeding singly accrued greater fitness at younger ages than cobreeding females. Accounting for the fitness birds would have obtained by breeding singly, however, lifetime inclusive fitness effects declined with coalition size for males, but were greater for females breeding as duos compared to breeding singly, due largely to indirect fitness effects of kin. Our analyses provide a road map for, and demonstrate the importance of, quantifying indirect fitness as a powerful evolutionary force contributing to the costs and benefits of social behaviors.

There are two main hypotheses for why offspring in cooperatively breeding taxa delay dispersal and remain on their natal territory rather than disperse. First, ecological constraints may force offspring to remain on their natal territory until a reproductive opportunity presents itself in an otherwise saturated habitat. Alternatively, delaying dispersal and helping kin may increase an offspring's inclusive fitness. One means by which offspring might enhance their direct fitness by delaying dispersal is by inheriting breeding status on their natal territory. Such territory inheritance regularly occurs in acorn woodpeckers, Melanerpes formicivorus, a species whose social groups consist of a cooperatively polygynandrous breeding core along with nonbreeding helpers of both sexes that are offspring from prior breeding efforts. Here we examine the life-history differences and the fitness consequences of birds attaining breeder status by either inheriting their natal territory or dispersing to a new territory. Despite significant differences in life history, including the mean territory quality on which individuals bred and mean co-breeder coalition size of breeders, we found no statistical differences in either direct or kin-selected (indirect) fitness benefits for breeders that inherited and dispersed. The incidence of birds engaging in both strategies, inheriting their natal territory and later dispersing, or dispersing but later returning to inherit their natal territory, further reduces the potential direct fitness benefits of inheritance relative to dispersal, since neither precludes the other. Territory inheritance is an important, alternative means of achieving breeding status in this population. However, ecological constraints to dispersal and kin-selected fitness benefits as a helper likely play larger roles driving the acorn woodpecker's extraordinary social system.

Seed dispersal mutualisms evolve in complex communities of plants and frugivorous animals, within which indirect interactions such as competition and facilitation can occur. Many tropical plants reproduce subannually in multiple episodes per year. Yet, the consequences of episodic reproduction on interactions with seed dispersers remain largely unexplored. We studied Guarea guidonia (Meliaceae), a subannually reproducing tree, to examine temporal variation in seed dispersal within a tropical forested landscape in the central Dominican Republic. We hypothesized that foraging by dispersers would (a) increase with daily ripe fruit set on focal trees, (b) decrease with increasing ripe fruit biomass of neighboring plants, and (c) decrease in response to the fruiting periods of other taxa at the landscape scale. Over 18 months, we tracked the phenology of 24 focal trees and quantified foraging during fruiting phases through repeated observations, simultaneously measuring seed dispersal in traps beneath isolated bird perches across the study landscape. Date was the only clear predictor of frugivore visitation, with early and late peaks in activity during the 5-month fruiting period. The midseason decline in foraging at focal trees matched a decline in Guarea dispersal to seed traps independently of fruit abundance. Declines in Guarea dispersal were inversely related to peak dispersal of higher quality lipid-rich fruiting species. Our results suggest that multiple flowering episodes and subsequent asynchronous fruit ripening of low-quality fruits can reduce competitive pressure from other higher quality fruiting species, implying that this potential bet-hedging strategy may be an overlooked factor in the evolution of subannual reproduction. Abstract in Spanish is available with online material.

Wood-decay fungi soften wood, putatively providing opportunities for woodpeckers to excavate an otherwise hard substrate, yet the fungal community composition in tree cavities and the specificity of these relationships is largely unknown. We used high-throughput amplicon sequencing of the fungal ITS2 region to examine the fungal communities associated with acorn woodpeckers (Melanerpes formicivorus) and their cavities in mature valley oak (Quercus lobata) and blue oak (Q. douglasii) trees in an oak savannah of central coastal California, USA. Acorn woodpeckers and their excavations harbored over 1500 fungal taxa, including more than 100 putative wood -decay fungi. The fungal communities found on the birds were more similar to those found in excavated cav-ities than those found in trees without excavated holes. These results suggest that symbiotic associations between acorn woodpeckers and fungi are highly diverse, with low specificity. Symbiotic associations between cavity -excavators and fungi are likely more common and widespread than previously thought.

Advances in data‐logging technologies have provided a way to monitor the movement of individual animals at unprecedented spatial and temporal scales. When used in conjunction with social network analyses, these data can provide deep insight into the structure and dynamics of animal social systems. Emergence of these new technologies demands concomitant progress in workflows to translate data streams from automated systems to social networks, based on biologically relevant metrics. Here we outline key considerations for constructing social networks from automated telemetry data. We highlight the need for paying particular attention to the spatial arrangement of receiver stations with respect to the ecology of study system and developing appropriate criteria for quantifying associations. We provide a case study for constructing social networks from automated telemetry data collected over 1 month during a study of acorn woodpeckers Melanerpes formicivorus , a cooperatively breeding bird. The data consisted of detections of known birds near receiver stations placed within core areas of group territories. We use this system to demonstrate how to build social networks to investigate biological questions about patterns of associations between group members and territory visitors across the landscape.

Although primary cavity-nesting species are capable of excavating new cavities, they often reuse old ones. To determine potential factors driving such reuse, we studied nest-cavity reuse in the Acorn Woodpecker (Melanerpes formicivorus), a cooperatively breeding species that reuses old cavities for 57.2% of nests at Hastings Reservation in central coastal California, USA. We found no evidence for significant fitness costs or benefits of cavity reuse compared to using newly constructed cavities. In contrast, several lines of evidence supported a role for constraints on both cavity reuse and on new cavity construction. The main constraint on reuse was cavities failing to survive from one year to the next, usually because the limb fell apart, filled with water, or was usurped by another species. Evidence that constraints on new cavity construction may be important included more frequent cavity reuse when groups renested and use of artificial cavities when they were experimentally provided. Nest-cavity reuse in this population appears to be driven primarily by constraints, including the energetic costs and time required to excavate a new cavity, rather than fitness consequences, even though Acorn Woodpeckers regularly excavate small holes in trees for acorn storage and the energetic costs of new cavity construction are apparently insufficient to significantly depress reproductive success. Constraints play a significant role in cavity reuse and may affect both the intraspecific and interspecific frequency of cavity reuse among facultative excavating species.

Natural selection is expected to favor males that invest more in offspring they sire. We investigated the relationship between paternity and male behavior in the acorn woodpecker (Melanerpes formicivorus), a cooperative breeder that lives in family groups including offspring that remain on their natal territory, sometimes for years, and cobreeders of both sexes. Regardless of group composition, only one communal nest is attended at a time. Whereas cobreeding females share maternity equally, one male usually sires the majority of young in the group's communal nest. Copulations are rarely observed, and thus it has not been possible to link paternity to sexual behavior. There were no differences among cobreeder males that did or did not sire young in their propensity to roost in the nest cavity at night. However, cobreeder males that attended females continuously prior to egg-laying were more likely to successfully sire young than males that did not, and the relative share of feeding visits and time spent at the subsequent nest were positively related to a male's realized paternity. These differences in male behavior were partly due to differences among males and partly to plasticity in male behavior covarying with paternity share. Feedings by males successfully siring young also involved a larger proportion of nutritionally valuable insect prey. Males are aware of their paternity success, apparently because of their relative access to females prior to egg laying, and provide more paternal care at nests in which they are more likely to have sired young.

The ecology of vector-borne diseases in a region can be attributed to vector-host interactions. In the United States, tick-borne pathogens are the cause of the highest number of reported vector-borne diseases. In the mid-Atlantic region of the eastern United States, tick-borne diseases such as Lyme disease, have increased in incidence, with tick-host-pathogen interactions considered a contributing factor to this increase. Ticks become infected with pathogens after taking a blood meal from a systemically infected host or through a localized infection while co-feeding on a host with other infected ticks. The host not only plays a role in pathogen acquisition by the tick, but can also facilitate dispersal of the tick locally within a region or over greater distances into new geographical ranges outside of their historical distributional range. In this study conducted in southeastern Virginia (USA), we examined the interaction between both resident and migratory bird species and Ixodes ticks, the primary vectors of Borrelia burgdorferi sensu stricto (s.s.) the main causative agent of Lyme disease on the East coast of the United States. Over a two-year period (2012-2014), 1879 passerine birds were surveyed, with 255 Ixodes ticks tested for the presence of Borrelia spp. Eighty passerine birds (4.3 %) representing 17 bird species were parasitized by at least one Ixodes tick, but only three bird species were parasitized by Ixodes ticks that tested positive for B. burgdorferi s.s. Twenty Ixodes ticks (7.8 %) tested positive for B. burgdorferi s.s. with nearly all collected from resident bird species including the Carolina wren (Thryothorus ludovicianus) and brown thrasher (Toxostoma rufum). Given that millions of birds pass through southeastern Virginia during migration, even with the low number of Ixodes ticks parasitizing passerine birds and the low prevalence of B. burgdorferi s.s. found within Ixodes ticks collected, the sheer volume of passerine birds suggests they may play a role in the maintenance and dispersal of B. burgdorferi s.s. in southeastern Virginia.

Cooperative breeding strategies lead to short-term direct fitness losses when individuals forfeit or share reproduction. The direct fitness benefits of cooperative strategies are often delayed and difficult to quantify, requiring data on lifetime reproduction. Here, we use a longitudinal dataset to examine the lifetime reproductive success of cooperative polygamy in acorn woodpeckers ( Melanerpes formicivorus ), which nest as lone pairs or share reproduction with same-sex cobreeders. We found that males and females produced fewer young per successful nesting attempt when sharing reproduction. However, males nesting in duos and trios had longer reproductive lifespans, more lifetime nesting attempts and higher lifetime reproductive success than those breeding alone. For females, cobreeding in duos increased reproductive lifespan so the lifetime reproductive success of females nesting in duos was comparable to those nesting alone and higher than those nesting in trios. These results suggest that for male duos and trios, reproductive success alone may provide sufficient fitness benefits to explain the presence of cooperative polygamy, and the benefits of cobreeding as a duo in females are higher than previously assumed. Lifetime individual fitness data are crucial to reveal the full costs and benefits of cooperative polygamy.

Although intergroup conflict is widespread in vertebrates, simultaneous agonistic interactions among several groups are rare [1Kitchen D.M. Packer C. Complexity in vertebrate societies.in: Keller L. Levels of Selection in Evolution. Princeton University Press, Princeton1999: 176-196Google Scholar]. Acorn woodpeckers (Melanerpes formicivorus) are cooperatively breeding birds that defend acorn storage facilities (‘granaries’), which provide significant survival and reproductive benefits to breeders in the social group [2Koenig W.D. Walters E.L. Stacey P.B. Stanback M.T. Mumme R.L. Acorn Woodpecker (Melanerpes formicivorus), version 1.0.in: Rodewald P.G. Keeney B.K. Birds of the World. Cornell Lab of Ornithology, Ithaca, NY2020https://doi.org/10.2173/bow.acowoo.01Crossref Google Scholar]. Breeder vacancies in high-quality territories (i.e., large granaries accrued over multiple generations) elicit violent fights or ‘power struggles’, among multiple same-sex coalitions from neighboring groups. Here, using an automated radio-telemetry system, we found that individuals in coalitions competing for breeding vacancies — the ‘warriors’ — invested up to ten hours per day on successive days before one coalition emerged victorious. Power struggles also attracted ‘spectators’— acorn woodpeckers not eligible to fill the breeding vacancy. Apparently present only to gain social information, spectators travelled from territories as far as over three kilometers away. Our study reveals the complexity of acorn woodpecker social group networks, demonstrating the significant effort of both warriors and spectators to pursue fitness benefits and obtain social information. Acorn woodpecker groups live on year-round territories defined by granaries, trees with hundreds to thousands of holes, drilled by the birds, where they store acorns for later consumption (Figure 1A). Stored acorns are consumed by adults when food is scarce and are also fed to nestlings. Granaries are pilfered by intra- and interspecific competitors and are thus zealously defended by all group members. Large-granary territories are often controlled by polygynandrous groups consisting of multiple male and female breeders and their non-breeding offspring (‘helpers’). Same-sex co-breeders are closely related to each other but unrelated to breeders of the opposite sex [3Koenig W.D. Walters E.L. Haydock J. Acorn woodpeckers: helping at the nest, polygynandry and dependence on a variable acorn crop.in: Koenig D. Dickinson J.L. Cooperative Breeding in Vertebrates: Studies of Ecology, Evolution and Behavior, W. Cambridge University Press, Cambridge2016: 217-236Crossref Scopus (8) Google Scholar]. In addition to within-group dynamics, acorn woodpeckers recognize associations among individuals outside their group and track membership changes in surrounding territories [4Pardo M.A. Sparks E.A. Kuray T.S. Hagemeyer N.D. Walters E.L. Koenig W.D. Wild acorn woodpeckers recognize associations between individuals in other groups.Proc. R. Soc. B. 2018; 285: 20181017Crossref PubMed Scopus (8) Google Scholar]. This information transfer is likely to occur via numerous daily off-territory forays to neighboring territories [5Barve S. Hagemeyer N.D. Winter R.E. Chamberlain S.D. Koenig W.D. Winkler D.W. Walters E.L. Wandering woodpeckers: foray behavior in a social bird.Ecology. 2020; 101e02943Crossref PubMed Scopus (5) Google Scholar]. A typical way that non-breeding helpers obtain a breeding position is by filling a breeder vacancy in a non-natal territory. In our California study population, same-sex coalitions of helpers will fight against a dozen or more competing coalitions (40 or more birds) for a breeding vacancy, with winners co-breeding at the new territory [6Hannon S.J. Mumme R.L. Koenig W.D. Pitelka F.A. Replacement of breeders and within-group conflict in the cooperatively breeding acorn woodpecker.Behav. Ecol. Sociobiol. 1985; 17: 303-312Crossref Scopus (63) Google Scholar]. Typically, a quarter of the about 50 groups we follow have a breeding vacancy in a given year; although long, violent power struggles that attract a large number of birds tend to happen at territories with big granaries [7Koenig W.D. Space competition in the acorn woodpecker: power struggles in a cooperative breeder.Anim. Behav. 1981; 29: 396-409Crossref Scopus (43) Google Scholar]. Such power struggles can last for several days and involve spread-wing displays (Figure 1A), incessant calling, and intense physical — sometimes fatal — fights [6Hannon S.J. Mumme R.L. Koenig W.D. Pitelka F.A. Replacement of breeders and within-group conflict in the cooperatively breeding acorn woodpecker.Behav. Ecol. Sociobiol. 1985; 17: 303-312Crossref Scopus (63) Google Scholar]. A key to understanding the factors driving the success of a coalition in achieving breeding status involves quantifying the effort expended by coalition members that travel to, and fight at, power struggles. However, visually monitoring behavior at power struggles — especially individual investment — is difficult due to the chaotic nature of these conflicts. Using an automated radio-telemetry system [5Barve S. Hagemeyer N.D. Winter R.E. Chamberlain S.D. Koenig W.D. Winkler D.W. Walters E.L. Wandering woodpeckers: foray behavior in a social bird.Ecology. 2020; 101e02943Crossref PubMed Scopus (5) Google Scholar], we tracked 36 acorn woodpeckers that attended three power struggles (2018: May, Aug.; 2019: Apr.). Because each power struggle was triggered by a female breeder vacancy, we expected helper females to invest the most effort as warriors [6Hannon S.J. Mumme R.L. Koenig W.D. Pitelka F.A. Replacement of breeders and within-group conflict in the cooperatively breeding acorn woodpecker.Behav. Ecol. Sociobiol. 1985; 17: 303-312Crossref Scopus (63) Google Scholar,7Koenig W.D. Space competition in the acorn woodpecker: power struggles in a cooperative breeder.Anim. Behav. 1981; 29: 396-409Crossref Scopus (43) Google Scholar]. Females with a breeding position at another group, as well as any males, were considered spectators, since such individuals were not relevant to the female vacancy. Although not the case with tagged birds in this study, it is possible that such individuals were assisting helper coalitions from their home groups (their own offspring). Given the tradeoff between gaining information at a power struggle vs. defending a home territory [5Barve S. Hagemeyer N.D. Winter R.E. Chamberlain S.D. Koenig W.D. Winkler D.W. Walters E.L. Wandering woodpeckers: foray behavior in a social bird.Ecology. 2020; 101e02943Crossref PubMed Scopus (5) Google Scholar], we did not expect to detect many spectators at power struggles. We used linear mixed models (Supplemental information) to test whether a bird’s role as a warrior or spectator explained variation in time spent at power struggles (i.e., number of minutes a tag was detected by a receiver at the granary), and distance traveled to reach power struggles from home territories. The three power struggles attracted about a third (31 ± 7%) of all radio-tagged birds in our study area (N = 41/61/73) at the time of each event. Some birds visited power struggles from over three kilometers away, close to the maximum distance between any two groups in our study area (Figure 1B). As expected, warriors spent the most time at the power struggles: helper females (total N = 13) attended power struggles for nearly 113 minutes longer per day (mean ± SE 112.8 ± 28.5 min) than spectators (N = 23, P < 0.001, Figure 1C). During one power struggle, two helper female coalition members returned over four consecutive days, staying over ten hours each day (Figure 1C), but did not win the power struggle; an untagged female coalition ultimately won the breeding position. Such a continuous presence at these conflicts demonstrates a remarkable willingness to expend intense short-term effort for potential access to the long-term benefits of a breeding position at a high-quality territory. Spectators spent almost an hour per day attending power struggles (mean ± SE = 52.1 ± 10.4 min/day, range 1–462 min; Figure 1B,D). This suggests that maintaining current information within the acorn woodpecker social network is worth leaving a home territory unattended for considerable periods of time. Warriors came from group territories that were significantly closer (mean ± SE = 644 ± 136 m) than spectators (1432 ± 167 m) (P < 0.001, Figure 1D). Additionally, there was no difference in the number of days warriors and spectators visited any one power struggle site (P > 0.05, Figure 1E). Spectators are thus clearly willing to repeatedly travel considerable distances, apparently even farther than those competing for the vacancy, to gather social information. Our study not only demonstrates the significant effort invested by some individuals to ensure long-term fitness benefits, but also reveals that social birds — including those that already have a breeding position — foray well beyond their home territory to gather social information [8Schliehe-Diecks S. Eberle M. Kappeler P.M. Walk the line—dispersal movements of gray mouse lemurs (Microcebus murinus).Behav. Ecol. Sociobiol. 2012; 66: 1175-1185Crossref PubMed Scopus (20) Google Scholar]. Automated radio-telemetry is thus a powerful tool that can help reveal individual investment in complex social behaviors like power struggles; future studies should link such social events to the flow of information through social networks [9Ryder T.B. Dakin R. Vernasco B.J. Evans B.S. Horton B.M. Moore I.T. Testosterone modulates status-specific patterns of cooperation in a social network.Am. Nat. 2020; 195: 82-94Crossref PubMed Scopus (10) Google Scholar,10Papageorgiou D. Christensen C. Gall G.E. Klarevas-Irby J.A. Nyaguthii B. Couzin I.D. Farine D.R. The multilevel society of a small-brained bird.Curr. Biol. 2019; 29: R1120-R1121Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. We thank David Winkler for help with the radio-telemetry technology. Russell Winter, Emily Goldberg, Megan Massa and Hannah Horowitz assisted with fieldwork. We thank Dr. Brandt Ryder and an anonymous reviewer for constructive comments. We thank the National Science Foundation for funding (grants IOS-1455881 and IOS-1455900). Download .pdf (.73 MB) Help with pdf files Document S1. one figure and experimental procedures