Noninvasive genetic surveys before and after a megafire detect displacement of migratory mule deer

Abstract

Due to climate change and past logging and fire suppression, the western US are experiencing increasingly large and frequent wildfires. Understanding how wildlife respond to these mega-fires is becoming increasingly relevant to protect and manage these populations. However, the lack of predictability inherent in such events makes studies difficult to plan. We took advantage of a large high-severity wildfire that burned adjacent to an ongoing study of mule deer (Odocoileus hemionus) on their summer range upslope of the fire to investigate their displacement onto our study area both immediately and upon their return to summer range the following year. We used spatial capture-recapture models in conjunction with noninvasive fecal DNA sampling to estimate density and non-spatial Pradel robust-design models to estimate apparent survival and recruitment rates. Compared to density before the fire, we observed an increase in deer density and an increase in per-capita recruitment rates one month after the fire. These findings suggest that the immediate response of at least some deer was to flee the fire upslope onto the study area rather than to downslope toward their winter range. These changes did not carry over into the following year, however, suggesting that deer formerly using the burned area as summer range may have returned there despite the high severity of the fire, or may have chosen new areas for their summer range. This suggests that, at least in the short term, the fire did not negatively affect the deer population.

Deer dietary responses to wildfire: Optimal foraging, individual specialization, or opportunism?

“…These observations qualitatively mirror those observed in previous studies, but differ somewhat in the timing. A study of mule deer in the Sierra Nevada of California that was interrupted by another large fire (King Fire in 2014) found that abundance of deer increased within the first 2 months on unburned sites adjacent to the fire, but had declined by the following year to pre‐fire levels (Brazeal et al., 2021). This observation could have reflected the timing of that fire relative to the migratory status of that population; shortly after the fire occurred on summer range, deer migrated to their wintering grounds before returning the following summer, whereas in the present study, nonmigratory deer could have remained continuously in the same habitats to which they escaped the fire.…”

“…Up to now, studies of deer responses to wildfire have primarily documented use of, but not dietary intake in, burned versus unburned sites after a wildfire (Brazeal et al., 2021; Cave et al., 2021). In general, deer tend to move out of burned sites to unburned sites immediately after fires and return to burned areas after varying timespans, depending on vegetation regeneration.…”

“…Up to now, studies of deer responses to wildfire have primarily documented use of, but not dietary intake in, burned versus unburned sites after a wildfire (Brazeal et al, 2021;Cave et al, 2021).…”

Animal migration in the Anthropocene: threats and mitigation options

“…Specifically, the frequency, size, and severity of wildfires have increased recently. Wildfires have been shown to displace migratory species such as mule deer (Brazeal, Sollmann & Sacks, 2021) and even bird species (tule geese, Anser albifrons elgasi), and can disrupt migratory behaviour, and increase both energetic demands and mortality risk (Overton et al, 2022). On the other hand, fire suppression can result in changes to habitat structure such as increased density of tree stands and understory (Gilliam & Platt, 1999).…”