Natal Territory Research Articles

Predation risk promotes delayed dispersal in the cooperatively breeding cichlid Neolamprologus obscurus

Delayed dispersal of offspring from the natal territory is an important process in the evolution of cooperative breeding. Ecological constraints such as habitat saturation can promote delayed dispersal. Thus far, the role of predation risk in the evolution of cooperative breeding systems has received less attention, although it is understood as an important ecological factor shaping dispersal patterns and social structure in animals. To bridge this gap, we analysed group structure and dispersal patterns of helpers within a population of the cooperatively breeding cichlid Neolamprologus obscurus. We conducted behavioural observations for a period of 3 months at two study sites within this population, which differed in predation risk and availability of unoccupied space. Furthermore, by combining field observations with molecular analyses, we assessed group structure to unravel the dispersal patterns of helpers. At the high predation risk location, we found that helpers (1) had a lower dispersal propensity, (2) dispersed shorter distances and (3) were generally larger. Furthermore, molecular analyses and body size measurements suggest that helpers may stay longer in the natal territory under high predation risk than under low predation risk. Groups contained more helpers in the high predation risk site, which indicates that high predation pressure leads to delayed dispersal of helpers. Unoccupied potential dispersal areas were larger in the high predation risk site, suggesting that habitat saturation did not account for the dispersal patterns. Our results suggest that predation pressure is the main factor limiting the dispersal of helpers in the cooperatively breeding cichlid fish N. obscurus, and might be overlooked in other studies focusing on the evolution of cooperative breeding systems.

Spatial and begging behaviours of juvenile Tawny Owls (Strix aluco) from fledging to independence under contrasting food conditions

The post-fledging dependency period (PFDP: from fledging to cessation of parental care) is a critical yet poorly studied life history transition phase during which juveniles mature and develop skills for independence. We studied the spatial and vocal behaviour of radio-tagged juvenile Tawny Owls in 41 broods from fledging to independence (56–84 days) in 6 years of contrasting food conditions. Dispersion and nocturnal movements increased during the first 20–30 days post-fledging, after which the young roamed the entire natal territory, indicating fully or almost fully developed flying skills. During the entire PFDP, siblings were strongly associated both during the day (mean inter-sibling distances decreased from 11 to 0.6 m from the first to the 30th day after fledging) and at night (mean distances decreased from 32 to 6 m during the same period), and rarely moved outside the borders of the parental home range. The probability of begging per 20-min nocturnal observation period increased from 21 % at fledging to 80 % at independence during years of good food supply, but remained high (>82 %) in years of poor food supply. No change was observed in nocturnal movement distances or begging rates during the last 5 days before juvenile independence. Hence, juvenile Tawny Owls old enough to survive on their own invested heavily in begging, with no noticeable signs of increased hunting or exploration of potential settling areas outside the natal range, until they were no longer fed by their parents.

Survival and dispersal of the Cyprus wheatear Oenanthe cypriaca, an endemic migrant

Many populations of European migrant bird species are declining and this may be driven by survival rates; however, there are few studies that can estimate true survival rates. Cyprus wheatears Oenanthe cypriaca are an endemic migrant that winter in East Africa: populations are probably not declining but are annually variable. We recorded territory occupation and reoccupation in a colour-ringed population of 45–69 pairs over a 4-year period (2010–2013) from April to August to measure apparent survival and determine how it varied with sex, age, breeding productivity and year. We then estimated true survival by correcting apparent survival for dispersal by recording territory shifts and how this also varied by sex, age, breeding productivity and year. Apparent annual survival rate varied significantly by sex, age and year (males 2011, 2012, 2013: 0.70, 0.50, 0.62; females: 0.56, 0.34, 0.47; chicks: 0.35, 0.19, 0.28) but was not affected by the productivity of a territory. An average of 1.1 % of males and 8.2 % of females were lost during breeding, where 5/7 lost females were found depredated during incubation. Adults did not usually change territories between years (87 % were resident and 99 % moved less than four territories between years) regardless of sex, productivity or year; chicks, independent of their sex, moved on average three territories away from their natal territory. After correcting apparent survival for the probability of dispersal, males had the highest true minimum annual survival compared to females which were very similar to chicks (males 2011, 2012, 2013: 0.77, 0.50, 0.65; females: 0.65, 0.35, 0.50; chicks: 0.64, 0.34, 0.49). The results indicate a very high survival rate for a small passerine migrant, although they are probably sufficiently annually variable to profoundly affect annual population dynamics. If females have a lower survival rate, the sex ratio at birth may be female-biased to compensate; alternatively, females may have longer range dispersal than we could measure, particularly if they respond to their mates not returning by moving territories, leading to underestimation of their true survival. A high survival rate may be due to the rarity of sparrowhawks on Cyprus and the wheatears relatively short distance migration.

Adult helpers increase the recruitment of closely related offspring in the cooperatively breeding rifleman.

Indirect fitness benefits gained through kin-selected helping are widely invoked to explain the evolution of cooperative breeding behavior in birds. However, the impact of helpers on productivity of helped broods can be difficult to determine if the effects are confounded by territory quality or if the benefit of helpers is apparent only in the long term. In riflemen Acanthisitta chloris, helping and group membership are effectively decoupled as adult helpers are individuals that have dispersed from their natal territory and live independently from breeders in "kin neighborhoods." Nevertheless, helpers direct their care toward close relatives, suggesting that helping provides indirect fitness benefits. The aim of this study was to examine the benefits of helpers to recipient offspring in the rifleman, investigating both short- and long-term effects. The total amount of food delivered to nestlings in helped broods was greater than that received by broods without helpers. This did not result in any short-term increase in nestling mass or nestling body condition nor was there any reduction in length of the nestling period at helped nests. However, helpers were associated with a significant increase in juvenile recruitment, with twice the proportion of fledglings surviving to the next breeding season from helped broods relative to unhelped broods. Thus, helpers gain indirect fitness by improving the survival of kin, and in contrast to a previous study of riflemen, we conclude that kin selection has played a key role in the evolution of cooperative breeding in this species.

Primate archaeology reveals cultural transmission in wild chimpanzees (Pan troglodytes verus).

Recovering evidence of past human activities enables us to recreate behaviour where direct observations are missing. Here, we apply archaeological methods to further investigate cultural transmission processes in percussive tool use among neighbouring chimpanzee communities in the Taï National Park, Côte d'Ivoire, West Africa. Differences in the selection of nut-cracking tools between neighbouring groups are maintained over time, despite frequent female transfer, which leads to persistent cultural diversity between chimpanzee groups. Through the recovery of used tools in the suggested natal territory of immigrants, we have been able to reconstruct the tool material selection of females prior to migration. In combination with direct observations of tool selection of local residents and immigrants after migration, we uncovered temporal changes in tool selection for immigrating females. After controlling for ecological differences between territories of immigrants and residents our data suggest that immigrants abandoned their previous tool preference and adopted the pattern of their new community, despite previous personal proficiency of the same foraging task. Our study adds to the growing body of knowledge on the importance of conformist tendencies in animals.

Long-distance dispersal connects Dinaric-Balkan and Alpine grey wolf (Canis lupus) populations

In the last two centuries, persecution and deforestation caused grey wolf Canis lupus populations in Europe to decline. Recently, their numbers started to recover although most populations still remain isolated from one another. This study presents the first documented evidence of the successful reconnection of the Dinaric-Balkan and the Alpine wolf populations via long-distance dispersal and subsequent reproduction. A young male wolf radiocollared in the Dinaric Mountains in July 2011 travelled through Slovenia and Austria to the Italian Alps, where he settled in March 2012. During the 98 days of dispersal period, the wolf has travelled a cumulative line distance of 1176 km crossing multiple anthropogenic and natural barriers, and successfully hunting wild prey until he settled 233 km straight line distance from its natal territory. Camera trapping, snow tracking and genetic evidence in the new territory confirmed pairing with a female wolf from the neighbouring Alpine population. In the following year, the pair has produced a first documented “mixed” litter between wolves from the Dinaric-Balkan and the Alpine wolf populations. This case study demonstrates the potential for the future merging of European wolf populations even in human-dominated landscapes and highlights the importance of transboundary cooperation in wolf research and management.

Calling Where It Counts: Subordinate Pied Babblers Target the Audience of Their Vocal Advertisements.

For territorial group-living species, opportunities to reproduce on the natal territory can be limited by a number of factors including the availability of resources within a territory, access to unrelated individuals, and monopolies on reproduction by dominant group members. Individuals looking to reproduce are therefore faced with the options of either waiting for a breeding opportunity to arise in the natal territory, or searching for reproductive opportunities in non-natal groups. In the cooperatively breeding Southern pied babbler, Turdoides bicolor, most individuals who achieve reproductive success do so through taking up dominant breeding positions within non-natal groups. For subordinate pied babblers therefore, searching for breeding opportunities in non-natal groups is of primary importance as this represents the major route to reproductive success. However, prospecting (where individuals leave the group to search for reproductive opportunities within other groups) is costly and individuals rapidly lose weight when not part of a group. Here we demonstrate that subordinate pied babblers adopt an alternative strategy for mate attraction by vocal advertisement from within their natal territories. We show that subordinates focus their calling efforts on the edges of their territory, and specifically near boundaries with neighbouring groups that have potential breeding partners (unrelated individuals of the opposite sex). In contrast to prospecting, calling individuals showed no body mass loss associated with this behaviour, suggesting that calling from within the group may provide a ‘cheap’ advertisement strategy. Additionally, we show that subordinates use information regarding the composition of neighbouring groups to target the greatest number of potential mating partners.

Natal territory size, group size, and body mass affect lifetime fitness in the cooperatively breeding Florida Scrub-Jay

ABSTRACT Early rearing conditions can have profound short- and long-term effects on survival and reproduction of vertebrates. In cooperatively breeding birds, where variable social conditions interact with other sources of environmental variation, fitness consequences of the natal environment are of particular interest. We used data from a long-term study of the Florida Scrub-Jay (Aphelocoma coerulescens) to examine how characteristics of the natal brood, territory, and social group interacted to influence future survival and reproduction. Nestling and juvenile body mass were significant positive predictors of survival from fledging through the first year of life. The area of oak scrub in the natal territory correlated positively with nestling and juvenile body mass and had two long-term consequences: it was positively related to the probability of becoming a breeder and negatively related to age at first breeding, particularly for males. Effects of natal group size were complex and partially dependent on...

Ontogenic patterns of scent marking in red foxes, Vulpes vulpes (Carnivora: Canidae)

Scent marking is widely recognised to have a crucial function in many species. Most research has focussed on adults and very little is known about scent marking patterns during juvenile development. Using video records of juvenile red fox Vulpes vulpes across 6 years, we tested whether scent marking rates varied with age or sex, or whether juveniles remaining on the natal territory (philopatry) marked more frequently than those that disappeared. Our data show that male juvenile red foxes scent marked more than females during early development, but rates rapidly declined as they aged. In contrast, females showed a significantly later and slower rate of decline. Within females, individuals that remained in the natal area had higher scent marking rates than those that disappeared, suggesting that scent marking has a role in social group affiliation within litters. These results demonstrate that scent marking plays an important role in juveniles, including their intra-litter social interactions.

Effects of territory size on the reproductive success and social system of the giant otter, south‐eastern Peru

AbstractThe link between resource abundance, dispersion and cooperative breeding in mammals has been a topic of much debate among ecologists. The giant otter social system is facultatively cooperative. Extended families inhabit home ranges where only a dominant pair breeds, and other family members assist with cub defence and food provision. But this system can be affected by local ecology. In the floodplain of the Manu River, in Manu National Park, Peru, oxbow lakes are patchily distributed and form the resource‐rich cores, or territories, of giant otter family home ranges. We present data from a long‐term study at this site, linking territory size variability to the composition of resident giant otter groups and their reproductive success. Territory size predicts group structure; both the size of groups and the number of post‐emergence cubs are positively correlated to the total lake area within the group territory. Territories with small lake areas (likely to be poor territories) often support only a pair, and the pair may not breed successfully every year. Cubs are more likely to survive in years when more non‐breeding adults are present at the time of emergence. However, there may be a negative effect on survival where more non‐breeding adults are present in the subsequent year. Finally, cubs produced in larger territories are more likely to disperse and breed successfully away from the natal territory. We conclude that giant otter societies are likely shaped by the spatial dispersion of lakes, and food abundance and dispersion within these rich patches.

Kin aggression and resource availability influence phenotype-dependent dispersal in a passerine bird

Understanding the causes of dispersal is important as it strongly influences population dynamics and evolution. However, context dependency of dispersal decisions, such as effects of social interactions and resource availability, is rarely disentangled from intrinsic factors, such as animal personality. Western bluebirds provide a unique opportunity to investigate the relative importance of intrinsic versus extrinsic factors in dispersal decisions because they display distinct aggressive personality types, have high recruitment of sons to the natal population, and depend on nest cavities, a resource that is easy to quantify. Here, we measured territorial interactions among kin and non-kin, resource availability, and aggressive behavior over an 11-year period to determine how they influenced dispersal decisions of male offspring. We found that distance dispersed from kin was driven by a male’s own aggression, the aggression of his nearest kin, and the resources available on the natal territory. Both aggressive males and males with aggressive kin dispersed longer distances, as did males who had fewer resources on their natal territories. Thus, dispersal in this species is influenced jointly by intrinsic and extrinsic factors. Because resource acquisition and personality type are interdependent in this species, changes in the social environment are likely to have important consequences for population dynamics.

Sex difference in travel is concentrated in adolescence and tracks reproductive interests.

Sexual selection theory suggests that the sex with a higher potential reproductive rate will compete more strongly for access to mates. Stronger intra-sexual competition for mates may explain why males travel more extensively than females in many terrestrial vertebrates. A male-bias in lifetime distance travelled is a purported human universal, although this claim is based primarily on anecdotes. Following sexual maturity, motivation to travel outside the natal territory may vary over the life course for both sexes. Here, we test whether travel behaviour among Tsimane forager-horticulturalists is associated with shifting reproductive priorities across the lifespan. Using structured interviews, we find that sex differences in travel peak during adolescence when men and women are most intensively searching for mates. Among married adults, we find that greater offspring dependency load is associated with reduced travel among women, but not men. Married men are more likely to travel alone than women, but only to the nearest market town and not to other Tsimane villages. We conclude that men's and women's travel behaviour reflects differential gains from mate search and parenting across the life course.

Post-fledging dispersal and habitat use of a reintroduced population of the Crested Ibis (Nipponia nippon)

BackgroundKnowledge of dispersal movement of birds and their habitat preference during the post-fledging period is fundamental to the understanding of their ecological and evolutionary processes. The Crested Ibis is now being reintroduced to protected sites within its historical range, with the goal of establishing a self-sustaining population that may eventually qualify the species for delisting.MethodsWe carried out an ecological study of post-fledging dispersal and habitat use of a reintroduced population of the Crested Ibis (Nipponia nippon) from 2008 to 2012 in Ningshan County, China, by using banding and radio-telemetry methods.ResultsIn about two weeks (an average of 14.3 days) after fledging, the activities of the fledglings were concentrated in a range of about 100 m around their natal sites, such as the oak-pine forest patches at the edge of open habitats. During this period, fledglings were still partially dependent upon parental care and fed typically on a daily basis. Siblings increasingly became independent by mid-August and then gradually moved away from their natal sites to post-fledging dispersal locations. During the period of the post-fledging dispersal process, most juveniles moving southwest were concentrated at the mean direction (μ = 254.6°, š = 70.5°) with a mean dispersal distance of 5.1 km. It took an average of 56.4 days to disperse from the natal territory to the first wintering area. Also, forging habitats for juvenile ibis varied with time and local conditions. For example, paddy fields were used most frequently among all habitat types, while shallow rivers just from August to October. Masson pine (Pinus massoniana) was often regarded as the roosting tree species preferred by the Crested Ibis, with the highest utilization rate among all the roosting habitat types. The juveniles of the wild population dispersed four times as far as that of the reintroduced population, but the overall pattern of post-fledging dispersal is similar for the reintroduced and wild populations.ConclusionsOur results are very useful for us to predict the distance and direction of dispersal under various landscape conditions in other released sites. The project is a good example for reintroducing endangered species to their former ranges, and will be valuable for the protection of reintroduced populations of this critically and other endangered species.

Dispersal in an extensive continuous forest habitat: Marsh Tit Poecile palustris in the Białowieża National Park

Dispersal is one of the least understood features in the life-history of organisms. Theoretical work concentrates on explaining dispersal of organisms in patchy and heterogeneous landscapes, but there are few predictions of dispersal patterns in stable, spatially extensive and largely homogenous landscapes, such as large forests. It is expected that we should observe short-distance dispersal in such places, that, to avoid competition with parents and siblings and incestuous mating, offspring should leave natal patches (natal dispersal), disperse independently in different directions, and move over distances that efficiently minimise the probability of meeting a sibling. Breeding dispersal should be very limited, site tenacity should prevail. To explore these ideas, I use observations of Marsh Tits Poecile palustris (a small passerine specialist of mature forests) made in the strictly protected part of the Bialowieza National Park (Poland) over 21 years. The birds largely followed expectations: all fledglings left their natal territories and dispersed in different directions, and males moved shorter distances than females (median = 570 vs. 1,720 m). Apart from this difference, no influence of population density, fledgling time or family size was observed. No parent–offspring pairing occurred, with just one case of sibling–sibling pairing. After first breeding, individuals remained site-tenacious, as breeding dispersal distances were very short (median ca. 100 m). Such behaviour renders Marsh Tit poorly adapted to cross barriers and undertake long-distance movements, and this is actually observed in fragmented landscapes. Understanding dispersal patterns of organisms from extensive environments would be thus of value for basic and conservation science alike.

Song sharing with neighbours and relatives in a cooperatively breeding songbird

Kin recognition is important in allowing cooperative breeders to invest preferentially in helping kin, especially when helping is not restricted to the natal territory. Where spatial cues are not reliable indicators of kinship, animals can use family signatures, which may be learned or genetic. Alternatively, they can use unique signatures that are learned via prior experience in a context that identifies specific individuals as kin. Here we investigate sharing of song types between related and unrelated male western bluebirds, Sialia mexicana, a cooperatively breeding songbird that lives in neighbourhoods composed of a mix of kin and nonkin. Helpers only assist in raising close kin, including parents as well as brothers and grandfathers living on non-natal territories. In a previous study, we demonstrated that western bluebird males are able to recognize related males through their songs. Here we ask whether this kin recognition is based on song sharing within a family or whether western bluebird song sharing is primarily with neighbouring birds regardless of relatedness. The results indicate that western bluebirds often share with related and unrelated neighbours alike, and they rarely share any notes with non-neighbouring birds, whether they are related or unrelated. Although we cannot rule out the possibility of kin signatures that were not measurable using tools currently available for detecting vocal similarity, our findings suggest that kin recognition through song does not rely on note sharing with relatives and that western bluebirds use a more broadly applicable mechanism of vocal kin recognition compared to other cooperative breeders.

Delayed dispersal in western bluebirds: teasing apart the importance of resources and parents

Delayed and localized dispersal are fundamental life-history traits associated with formation of family groups and kin neighborhoods. Although the field has focused mainly on resource benefits and ecological constraints as drivers of delayed dispersal, social benefits of nepotism can also be important. Resources and nepotism are theoretically correlated as the affordability of nepotism scales with resource abundance. Rarely have both been analyzed simultaneously within a single analysis. Western bluebird sons (Sialia mexicana) stay in family groups on mistletoe-based territories for winter, disperse locally to form kin neighborhoods in spring, and have a low level of facultative helping by sons, brothers, and grandsons. Although a son’s tendency to remain on the natal territory increased with the number of parents present, mistletoe volume on the natal territory was a good predictor of sons staying home only for groups where the mother alone was present. Overwinter survival of sons was exceptionally high (95%) such that neither resources nor parental presence predicted survival advantages during the first year of life. When sons stayed on their natal territory for winter, their spring presence increased with the volume of mistletoe on their winter territory and was higher if they wintered with at least 1 parent. Stay-at-home sons acquired a portion of their parents’ territory in spring, including mistletoe that scaled with their parents’ mistletoe wealth. Our results indicate that although resources are undoubtedly important for the maintenance of family ties, the importance of maintaining connections with parents is underappreciated in studies of cooperative breeding.

Multiple socioecological factors influence timing of natal dispersal in kangaroo rats

Natal dispersal is an important event in the life history of many species. Timing of natal dispersal can influence survivorship and subsequent reproductive success. A variety of individual proximal factors determine if and when offspring disperse from the natal territory by influencing the costs of dispersing and the benefits of delaying dispersal. I examined the influence of multiple factors on dispersal age in the banner-tailed kangaroo rat (Dipodomys spectabilis), a solitary species lacking extreme sex-biased dispersal. I used an information theoretic approach to compare Cox proportional hazards regression models of dispersal age for 121 offspring over a 3-year period consisting of low and high population densities. The top-ranked models indicated that dispersal age was influenced by a combination of socioecological factors related to resource competition, environmental conditions, kin competition, and a lesser extent sex. Circumstances that likely reduced the probability of successful dispersal such as intense resource competition at high population density and being born earlier in the breeding season when environmental conditions were poor lead to longer delays in natal dispersal. Offspring in larger litters also dispersed earlier possibly to avoid competition with kin. Sex was weakly supported in top models but may only influence dispersal age at high population densities. These results suggest that the proximal factors that trigger dispersal are influenced by a combination of multiple effects related to the costs of dispersing and the benefits of remaining at home, even in species that do not form long-term social groups or have extreme sex-biased dispersal.

Habitat use and ranging behaviour of juvenile Golden Eagles Aquila chrysaetos within natal home ranges in boreal Sweden

Capsule Fledgling Golden Eagles in northern Sweden preferred clearcuts and other open forest habitats, as well as steep slopes.Aims To study the post-fledging habitat use and ranging behaviour of juvenile Golden Eagles on their natal territories.Methods Fourteen juvenile Golden Eagles in northern Sweden were marked with GPS transmitters and tracked until they left their natal territory.Results Eagles fledged at the end of July–beginning of August and remained on their natal territories until October–early November. Fledged eagles' home range size before flying south was on average 41 km2. Juvenile eagles showed a preference for clearcuts, coniferous forest on lichen-covered bedrock and edges between clearcuts and forest, whilst all other habitat types were used less than expected. The eagles showed a preference for steep slopes, in particular south-facing ones, whilst north-facing slopes were used less than expected.Conclusion Golden Eagles' preference for clearcuts and steep slopes can be used in the planning and management of ‘eagle friendly’ wind farms.

Philopatry, natal dispersal, first settlement and age of first breeding of bearded vultures Gypaetus barbatus in central Pyrenees

Capsule Male bearded vultures tended to disperse closer to natal territories than females with a preferred eastward natal dispersal direction. In general, birds settled for the first time in breeding territories at an average age of 7.6 years, first breeding attempt occurred at 10.0 years and first successful breeding at 10.4 years. Measures aimed at favouring the settlement of new pairs in the edge of their current distribution area would allow natural range expansion of this endangered species.

Reexamining Cooperative Hunting in Harris's Hawk (Parabuteo unicinctus): Large Prey or Challenging Habitats?

— 548 — The Auk, Vol. 130, Number 3, pages 548−552. ISSN 0004-8038, electronic ISSN 1938-4254.  2013 by The American Ornithologists’ Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Rights and Permissions website, http://www.ucpressjournals. com/reprintInfo.asp. DOI: 10.1525/auk.2013.120063 3Present address: 64340 Fogg Lane, Pearl River, Louisiana 70452, USA. E-mail: jacoulson@aol.com In group-living carnivores, cooperative hunting may be a cause or a consequence of cooperative breeding. Harris’s Hawk (Parabuteo unicinctus), a raptor that hunts and nests in cooperative groups of 3 to 7 hawks (Mader 1975a, b; Bednarz 1987; Dawson and Mannan 1989), provides an opportunity to examine benefits and possible causes of sociality because its cooperation is facultative and the species is relatively well studied. Attempts to demonstrate factors that promoted the evolution of cooperative breeding in Harris’s Hawks have mostly been unsuccessful. For example, the reproductive performance of groups did not differ from that of pairs (Mader 1975b, Bednarz 1987). And, for the most part, researchers did not find differences in the habitat quality or the resources available in territories occupied by groups versus pairs (Bednarz and Ligon 1988, Dawson and Mannan 1991b). However, Bednarz (1988) demonstrated net energetic benefits for hunting parties of 5 or 6 hawks and proposed that cooperative hunting led to social living in Harris’s Hawk. Here, we support and extend this argument with a reinterpretation of data from the published literature, including an overlooked finding of significance. We hypothesize that one benefit of cooperative hunting is to increase success in habitats that make the prey difficult to catch (e.g., a high density of hiding places). We think that this benefit could be as important as capturing and overwhelming large prey, a benefit proposed by Bednarz (1988). We propose the “challenging habitats hypothesis” (CHH), similar to an idea proposed by Dawson (1988), as an additional or alternative explanation for the maintenance and, possibly, the evolution of cooperative hunting in Harris’s Hawk. As falconers, we developed this hypothesis after many years of hunting with single and cooperative groups of 2 to 8 Harris’s Hawks in a variety of habitats. We hope to rekindle scientific inquiry into cooperation in this species. In cooperatively breeding birds, helpers are usually offspring that delay natal dispersal. Factors proposed to explain delayed dispersal include a lack of suitable breeding territories and other ecological constraints such as a lack of available mates (Selander 1964, Emlen 1982); increased probability of survival and of inheriting the natal territory (Stacey and Ligon 1987, 1991); and high-survival, K-selected life-history traits, and low turnover of territories (Brown 1974, Ricklefs 1974, Arnold and Owens 1998). Kin selection may maintain helping in relatives, whereas helping in non-kin is maintained by reciprocity, intraspecific mutualism, or manipulation (Trivers 1971; Clutton-Brock 2002, 2009). These hypotheses are not mutually exclusive, and some or all probably help explain cooperative breeding in many cases (Hatchwell and Komdeur 2000, Pen and Weissing 2000).