Predicting performance of naïve migratory animals, from many wrongs to self-correction

Abstract

Migratory orientation of many animals is inheritable, enabling inexperienced (naïve) individuals to migrate independently using a geomagnetic or celestial compass. It remains unresolved how naïve migrants reliably reach remote destinations, sometimes correcting for orientation error or displacement. To assess naïve migratory performance (successful arrival), we simulate and assess proposed compass courses for diverse airborne migratory populations, accounting for spherical-geometry effects, compass precision, cue transfers (e.g., sun to star compass), and geomagnetic variability. We formulate how time-compensated sun-compass headings partially self-correct, according to how inner-clocks are updated. For the longest-distance migrations simulated, time-compensated sun-compass courses are most robust to error, and most closely resemble known routes. For shorter-distance nocturnal migrations, geomagnetic or star-compass courses are most robust, due to not requiring nightly cue-transfers. Our predictive study provides a basis for assessment of compass-based naïve migration and mechanisms of self-correction, and supports twilight sun-compass orientation being key to many long-distance inaugural migrations.

Gauge-and-compass migration: inherited magnetic headings and signposts can adapt to changing geomagnetic landscapes

“…Angular quantities, i.e., headings and inclination or declination signposts, were sampled using a von Mises distribution, the circular equivalent of a normal distribution, governed by the von Mises concentration, κ (57). For interpretability, we report circular precision and variability by , nearly equivalent to circular standard deviation for σ < 30° (16,57).…”

“…Flight-steps lasted from 90 minutes after sunset until 90 minutes before sunrise (54), for minimally 6 hours and maximally 12 hours, or until land was in sight. Flight durations were calculated using the algebraic formula for sunset hour for a spherical Earth based on date and latitude (68, and see 16). We considered a 15° default precision among flight-steps (κ=14.6), consistent with in-flight measurements of migrating songbirds (69,70) and model predictions of required precision (16,19).…”

“…Regarding robustness to temporal variability, it is important to consider whether plasticity in inheritance of orientation cues (11,36,37) can track temporal geomagnetic shifts at a population level. In order to assess this, since migratory headings will vary geographically (16,37,38), and are typically inherited as averages (11,39, but see 38), it is important to account for trans-generational changes (mixing) in orientation (11,37). For example, natal dispersal will create population-level variation among individual migratory headings (40,41).…”

“…To assess the long-term viability of inherited magnetic-based migration at the population level, including the benefit of inherited magnetic signposts, we developed a model of migration through spatiotemporally-varying geomagnetic landscapes using an evolutionary algorithm approach (45,46). The migration model is based on compass-based movement (16), extended to include signposted directional switches in the migratory direction. The evolutionary algorithm mimics inheritance of migratory orientation among successful migrants, accounting for both spatial population mixing (through natal dispersal) and stochastic variation in inheritance (36,43,47).…”

“…With a primary magnetic migratory compass, flight directions on departure (e.g., nightly) are determined relative to the proximate geomagnetic field. An in-flight magnetic compass can also be cue-transferred on departures from a primary geographic (star) or sun compass (16,33). To focus on magnetic-based migration, we by default modelled inherited magnetic headings with both a primary and in-flight magnetic compass.…”