Capture of satellites during planetary encounters

Context. Single-binary scattering may lead to an exchange where the single object captures a component of the binary, forming a new binary. This has been well studied in encounters between a star–planet pair and a single star. Aims. Here we explore the application of the exchange mechanism to a planet–satellite pair and another planet in the gravitational potential of a central star. As a case study, we focus on encounters between a satellite-bearing object and Neptune. We investigate whether Neptune can capture satellites from that object and if the captured satellites have orbits analogous to the Neptunian moons Triton and Nereid. Methods. Using N-body simulations, we study the capture probability at different encounter distances. Post-capture, we use a simple analytical argument to estimate how the captured orbits evolve under collisional and tidal effects. Results. We find that the average capture probability reaches ~10% if Neptune penetrates the donor planet’s satellite system. Most moons grabbed by Neptune acquire highly eccentric orbits. Post-capture, around half of those captured, especially those on tight orbits, can be circularised, either by tides only or by collisions+tides, turning into Triton-like objects. Captures further out, on the other hand, stay on wide and eccentric orbits like that of Nereid. Both moon types can be captured in the same encounter and they have wide distributions in orbital inclination. Therefore, Triton naturally has a ~50% chance of being retrograde. Conclusions. A similar process potentially applies to an exoplanetary system, and our model predicts that exomoons can jump from one planet to another during planetary scattering. Specifically, there should be two distinct populations of captured moons: one on close-in circular orbits and the other on far-out eccentric orbits. The two populations may have highly inclined prograde or retrograde orbits.

Fitness of the pestiferous small rodent Mastomys natalensis in an agroecosystem in Mayuge district, Lake Victoria Crescent, Uganda

A 2.5-year study was conducted to understand the fitness of Mastomys natalensis in an agroecosystem in relationship with environmental predictors. The study was conducted in Mayuge district, in the Lake Victoria Crescent zone in Eastern Uganda. Fitness was measured in terms of survival, maturation and capture probability and estimated using multi-event capture-recapture models. Survival rates were higher after high rainfall in the previous month and increased with increasing population density of the animals. Maturation rate, on the other hand, showed no significant association with any predictor variables, while capture probability was significantly associated with sex of the animals, with higher capture probability for males. The results demonstrate that the fitness of M. natalensis in an agroecosystem is dependent on rainfall, sex and current population density. The aforementioned results were associated with increasing vegetation which provides cover for animal nesting and abundant food for the animals during rainfall periods and thus increased survival, high mobility in males in search for mates thus exposing animals to high chances of being captured and increased prey saturation at high population density resulting in high animal survival. These results have important implications for the timing of management strategies, i.e. control efforts should be enforced during the rainfall seasons to prevent high population buildup in the succeeding seasons.

Survival, dispersal, and capture probability of male and female birds

In birds, observed adult sex ratios often are biased towards males. This bias could arise due to differences between sexes in dispersal or in detectability / catchability, but a preferred explanation has been sex differences in survival. However, most studies investigated apparent survival, in which differences in dispersal were not accounted for. Here, we used data from 24'830 capturesof 11 bird species, collected at 40 Hungarian constant effort ringing sites, to estimate true survival, dispersal, and capture probability. On average, dispersal and capture probabilities were similar between sexes. However, the probability to survive from one year to the next was 0.46 in males but only 0.37 in females, suggesting that higher female mortality may indeed be the most important predictor of male-biased adult sex ratios.