Stephen F. Matter

Fish movement in freshwater streams is often tied to patterns of flow, especially when the stream is intermittent, flashy, or some combination thereof. Relationships between flow and fish movement are exacerbated in small urban streams in impervious surface‐dominated watersheds that lead to extreme flow conditions. Here we examined the response of Creek Chub ( Semotilus atromaculatus ), a common pioneer fish species in eastern North America, to flow events of various sizes in a small intermittent urban headwater stream. Our primary goals were to determine (1) the level of Creek Chub movement occurring in an intermittent headwater stream, (2) the influence of flow on movement direction and magnitude, (3) the degree of variation in individual movement behaviour, and (4) mortality rates in the system. The study used PIT tagging and telemetry surveys to monitor Creek Chub movement over a six‐month period. We found that individual Creek Chub in our study system were generally mobile (71%), but usually moved short distances only; however, a few individuals moved much farther, with a maximum single movement of 521 m. Moderate or major flow events increased the probability and magnitude of Creek Chub movement, but there was no detectable asymmetry towards upstream or downstream directionality. Movement was variable among individual fish and fish were able to respond to large and small flow events to move among habitats. Finally, we observed relatively high, but episodic, mortality in our study site, potentially related to pollution events. Evidence of elevated mortality points to the potential importance of movement in highly disturbed streams, as it may enable recolonization after local extirpation.

How first‐time animal migrants find specific destinations remains an intriguing ecological question. Migratory marine species use geomagnetic map cues acquired as juveniles to aide long‐distance migration, but less is known for long‐distance migrants in other taxa. We test the hypothesis that naïve Eastern North American fall migratory monarch butterflies ( Danaus plexippus ), a species that possesses a magnetic sense, locate their overwintering sites in Central Mexico using inherited geomagnetic map cues. We examined whether overwintering locations and the abundance of monarchs changed with the natural shift of Earth's magnetic field from 2004 to 2018. We found that migratory monarchs continued to overwinter at established sites in similar abundance despite significant shifts in the geomagnetic field, which is inconsistent with monarchs using fine‐scale geomagnetic map cues to find overwintering sites. It is more likely that monarchs use geomagnetic cues to assess migratory direction rather than location and use other cues to locate overwintering sites.