The time frame of home-range studies: from function to utilization

Socioecological factors influencing intraspecific variation in ranging dynamics of western lowland gorillas (Gorilla gorilla gorilla) in Ndoki Forest

Ranging dynamics are physical and behavioral representations of how different socioecological factors affect an organism's spatial decisions and space use strategies. Western lowland gorillas (Gorilla gorilla gorilla) are a model species to investigate the drivers of spatial dynamics based on both the natural variation in socioecological factors within the species and compared with their mountain gorilla counterparts. In this study, we evaluate the influences of resource seasonality and social dynamics on variation in home range size, utilization, and intergroup overlap among multiple gorilla groups over an 8-year study period in the northern Republic of Congo. This study shows that western lowland gorillas can have small home ranges comparable to mountain gorillas, rather than universally larger home ranges as previously supposed, and that home ranges are stable through time. The largest source of variation in space use was the degree of intergroup home range overlap. The study groups did not demonstrate intraspecific variation in range size nor changes in intergroup overlap with respect to seasonality of fruit resources, but all groups demonstrated expansion of monthly range and core area with group size, matching predictions of intragroup feeding competition. These findings highlight the potential impact of intergroup relationships on space use and prompt further research on the role of social dynamics in ranging strategies. In this study, we reveal a greater degree of variability and flexibility in gorilla ranging behavior than previously realized which is relevant to improving comparative studies and informing conservation strategies on behalf of these endangered primates.

A Systematic Review of Within-Population Variation in the Size of Home Range Across Ungulates: What Do We Know After 50 Years of Telemetry Studies?

Studying the factors determining the sizes of home ranges, based on body mass, feeding style, and sociality level, is a long-standing goal at the intersection of ecology and evolution. Yet, how species-specific life history traits interact with different components of the landscape to shape differences in individual home ranges at within-population level has received much less attention. Here, we review the empirical literature on ungulates to map our knowledge of the relative effects of the key environmental drivers (resource availability, landscape heterogeneity, lethal and non-lethal risks) on the sizes of individual home ranges within a population and assess whether species' characteristics (body mass, diet, and social structure), account for observed variation in the responses of the sizes of individual home ranges to local environmental drivers. Estimating the sizes of home ranges and measuring environmental variables raise a number of methodological issues, which complicate the comparison of empirical studies. Still, from an ecological point of view, we showed that (1) a majority of papers (75%) supported the habitat productivity hypothesis, (2) the support for the influence of landscape heterogeneity was less pervasive across studies, (3) the response of cattle-type to variation in food availability was stronger than the response of moose-type, and (4) species-specific body mass or sociality level had no detectable effect on the level of support to the biological hypotheses. To our surprise, our systematic review revealed a dearth of studies focusing on the ecological drivers of the variation in the sizes of individual home ranges (only about 1% of articles that dealt with home ranges), especially in the later decade where more focus has been devoted to movement. We encourage researchers to continue providing such results with sufficient sample sizes and robust methodologies, as we still need to fully understand the link between environmental drivers and individual space use while accounting for life-history constraints.

Home Range and Habitat Use of Breeding Black-Necked Cranes

Simple Summary

The Black-necked Crane is the only crane that breeds on the Qinghai–Tibetan Plateau, and it is currently classified as a vulnerable species. Habitat destruction and loss are the main threats for the Black-necked Crane. However, the breeding needs of Black-necked Cranes with regard to their preferred habitat remain unknown. To find the driving factors of their habitat selection, we studied the utilization rate of three habitats within the home range of Black-necked Cranes during four consecutive breeding stages. Black-necked Cranes mainly utilize meadows in the whole breeding season, followed by marsh meadows and marshes. Compared with other stages, the utilization of marsh habitat slightly increased in the postfledging stage. Since this stage is a very vulnerable period for young cranes, we suggest that grazing needs to be managed during this stage, that is, from late May to early September.

Abstract

To effectively protect a species, understanding its habitat needs and threats across its life-history stages is necessary. The Black-necked Crane (Grus nigricollis) is an endangered wetland bird species of the Qinghai–Tibetan Plateau, which is an important grazing area in China. To overcome the conflict between increasing grazing activities and the protection of wild cranes, we investigated the variation of habitat utilization within the home range of cranes at different stages (preincubation, incubation, postfledging, and fully fledged stages). We manually tracked 13 pairs of cranes in the Zoige international wetland, used the fixed-kernel-polygon (FKP) method to determine home-range size, and used satellite images to identify different habitat types. The average home-range size was 143.38 ± 34.46 ha. Cranes were most often located in meadow habitats followed by marsh meadows and marshes. During the postfledging stage, home-range size was significantly decreased, with the proportion of marsh habitat slightly increased. Since this stage is crucial for young-crane survival, research on the importance of marshes and effective protection measures should be further strengthened.

Distance sampling of duikers in the rainforest: Dealing with transect avoidance

Bushmeat is a major source of protein and income in tropical regions but is often over-harvested. A better monitoring of bushmeat stocks could help achieve sustainability. We used a combination of simulations and transect survey data collected from blue duikers (Philantomba monticola) in the Lomako wildlife reserve, Democratic Republic of the Congo, to investigate the use of transect-based distance sampling to monitor bushmeat stocks. The comparison of dung piles and direct observations of duikers evidenced that animals avoided both the transects in the absence of observers, and the observers themselves. This type of behavioural response appeared common in a literature survey. It causes a negative bias in the estimates of population densities from the standard distance sampling methodology. This negative bias would lead to over-pessimistic predictions of population viability, especially if the behavioural response is more intense in the locations where the animals are hunted. In turn, this would lead to excessively conservative management recommendations. To correct for the effect of the behavioural response of the animals to either the transects or the observers, we recommend recording both the forward and perpendicular distances to the observers (2D distance sampling), not just the perpendicular distance. We also recommend multiple-observer protocols. As a cautionary note, we also demonstrate a scenario where the intensity of the behavioural response is too high to reliably estimate the abundance of the population. As a perspective, we outline the general principles of a local stakeholder-based program combining distance sampling with less intensive types of ecological indicators to monitor wildlife populations.

The two oxpecker species reveal the role of movement rates and foraging intensity in species coexistence

The two Buphagus oxpecker species are specialized passerines that forage for ticks and other food particles on the body of ungulates in the African savannahs. One of their intriguing features is their ability to coexist despite sharing the same, specialized diet. Using co-occurrence data (photographs of giraffes with oxpeckers on them) and approximate Bayesian computing, we demonstrate that yellow-billed oxpeckers changed host faster than red-billed oxpeckers and appeared to displace red-billed oxpeckers from preferred giraffe body parts. Conversely, red-billed oxpeckers exhibited a fuller use of each host and displaced yellow-billed oxpeckers from distal giraffe body parts. These findings highlight that the partition of giraffe hosts in two separate niches was only part of the coexistence story in this species pair. More precisely, the oxpeckers shared the resource by exploiting it at different rates. They engaged in different trade-offs between giving-up density, patch discovery rate and competitor displacement ability. They illustrate the importance of the time frame of interactions.