Adult Danaus plexippus in southern Ontario frequently engage in soaring flight during their late summer migration. They utilize both ascending air currents (lift) produced by winds blowing up slopes and thermals (bubbles or columns of air that are rising because they are warmer and lighter than the surrounding air). The butterflies appear to be very efficient and exhibit different flying techniques when encountering various types of lift. When the weather is favourable, soaring is the main mode of flight and the butterflies achieve heights above the ground of at least 300 m. Extended soaring flight in thermals was always associated with tail winds.A sample of 18 specimens gave an average mass of 566 ± 81 mg and an average wing loading of 0.018 ± 0.002 g/cm2 (1.77 N/m2). Gliding performance parameters were measured for two specimens ballasted to 450 mg and the results were extrapolated to 600-mg individuals. The energetic advantages of utilizing soaring flight in terms of extension of maximum range is discussed.

Colonies of P. fuscatus that were initiated by various numbers of foundresses were studied to gather basic life table information. This information was used to estimate the selective advantage of foundress association according to a kin selection model, a parental manipulation model, two individual selection models, and a combined kin and individual selection model. Life table data were obtained for colonies located in exposed nest sites and for colonies located in nest sites provided with protection from vertebrate predators. Relative productivity of colonies produced by different size foundress associations and under different levels of predation pressure were determined. Multiple foundress colonies were found to be more productive and have an increased ability to re-establish after an episode of predation when compared with single foundress colonies. When predation levels on the colonies were high, multiple foundress colonies were more productive per colony and per foundress. When predation levels on the colonies were low, multiple foundress colonies were more productive per colony but less productive per foundress. At high levels of predation, when the queens and joiners were all assumed to have equivalent potential productivities, the kin selection model, the parental manipulation model, and the combined kin and individual selection model all predicted a selective advantage for joiners in foundress associations. At low levels of predation, when the wasps are assumed to have equivalent productivities, only the parental manipulation model predicted a selective advantage for joiners in foundress associations. When the assumption of equivalent potential is relaxed and when the wasps are assumed to be capable of detecting and acting upon individual differences in productivity, then all of the models could account for the existence of foundress associations. However, under this last set of assumptions the individual selection models require that the joiners have very low potential productivities.

A basic question concerning the monarch butterflies' fall migration is which monarchs succeed in reaching overwintering sites in Mexico, which fail-and why. We document the timing and pace of the fall migration, ask whether the sun's position in the sky is associated with the pace of the migration, and ask whether timing affects success in completing the migration. Using data from the Monarch Watch tagging program, we explore whether the fall monarch migration is associated with the daily maximum vertical angle of the sun above the horizon (Sun Angle at Solar Noon, SASN) or whether other processes are more likely to explain the pace of the migration. From 1998 to 2015, more than 1.38 million monarchs were tagged and 13,824 (1%) were recovered in Mexico. The pace of migration was relatively slow early in the migration but increased in late September and declined again later in October as the migrating monarchs approached lower latitudes. This slow-fast-slow pacing in the fall migration is consistent with monarchs reaching latitudes with the same SASN, day after day, as they move south to their overwintering sites. The observed pacing pattern and overall movement rates are also consistent with monarchs migrating at a pace determined by interactions among SASN, temperature, and daylength. The results suggest monarchs successfully reaching the Monarch Butterfly Biosphere Reserve (MBBR) migrate within a "migration window" with an SASN of about 57 • at the leading edge of the migration and 46 • at the trailing edge. Ninety percent of the tags recovered in Mexico were from monarchs tagged within this window. Migrants reaching locations along the migration route with SASN outside this migration window may be considered early or late migrants. We noted several years with low overwintering abundance of monarchs, 2004 and 2011-2014, with high percentages of late migrants. This observation suggests a possible effect of migration timing on population size. The migration window defined by SASN can serve as a framework against which to establish the influence of environmental factors on the size, geographic distribution, and timing of past and future fall migrations.

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