DISTRIBUTION AND RELATIVE ABUNDANCE OF ARIZONA FOREST BIRDS IN RELATION TO BURN SEVERITY

1
 
DISTRIBUTION AND RELATIVE ABUNDANCE OF ARIZONA
FOREST BIRDS IN RELATION TO BURN SEVERITY Chris
Kirkpatrick1, Courtney J. Conway2, and Patricia
B. Jones1 1 University of Arizona 2 USGS Arizona
Cooperative Fish and Wildlife Research Unit

• Results
• We observed evidence of fire at 406 of 1,513
  survey points 300 survey points had evidence of
  less severe fire and 106 survey points had
  evidence of severe fire.
• Median time since fire was 6 years (range 2-47
  years) for 82 of 406 burned survey points.
• We detected a total of 10,473 individuals of 97
  species and found associations between fire and
  bird presence/absence for 17 of 65 species
  analyzed and between fire and bird relative
  abundance for 25 of 16 species analyzed (Table
  1).

Table 1. Direction and strength of associations
between bird presence/absence and relative
abundance and two levels of burn severity using
data collected during montane forest bird surveys
in southeastern Arizona, April to July, 2000.

• Introduction
• Many montane forest birds in the southwestern
  U.S. (especially those inhabiting pine and
  pine-oak woodlands) evolved in areas that
  historically experienced recurrent (1 fire every
  decade), low- to moderate-severity surface fires.
• During the last century, grazing of surface
  fuels by introduced livestock and widespread fire
  suppression have greatly reduced the frequency of
  surface fires in the region.
• Marshall (1957, 1963) speculated that fire
  suppression and subsequent fuels accumulation had
  reduced the distribution and abundance of many
  open-woodland birds in the Sky Island
  mountain ranges of southeastern Arizona (Fig. 1).
• Increased fuel loads have resulted in a recent
  increase in the frequency of large, often severe
  wildfires (Fig. 2) and prompted the use of
  low-severity prescribed fires by land management
  agencies to reduce fuel loads.
• Despite the increasing frequency of wild and
  prescribed fires, few studies have examined the
  effect of fires (especially fires of different
  severities) on the unique avian community
  inhabiting montane forests of southeastern
  Arizona.

Presence/Absence Presence/Absence Relative Abundance Relative Abundance
Species Severe Fire Less-severe Fire Severe Fire Less-severe Fire
Hairy woodpecker n/a n/a
Greater Pewee n/a n/a
Western Wood-Pewee 0 0
White-breasted Nuthatch n/a n/a
Red-breasted Nuthatch -- -- n/a n/a
House Wren
Warbling Vireo -- -- -- 0
Yellow-rumped Warbler 0 - n/a n/a
Graces Warbler n/a n/a
Virginias Warbler 0 n/a n/a
Spotted Towhee 0 - -

• Methods Continued
• To control for elevation, we included elevation
  as a covariate in the regression models and
  restricted data for each species to the
  elevational range in which we observed the
  species.
• We included route as an independent variable in
  the regression models to control for the lack of
  independence between survey points along routes.
• We based our conclusions on the combined
  evidence of P-values from hypothesis testing and
  magnitudes of differences (odds ratios) generated
  from parameter estimation.

• Objectives
• To identify effects of recent fires (both severe
  and less-severe) on the distribution and relative
  abundance of forest birds in mountains of
  southeastern Arizona.

• Methods
• From April to July 2000, we conducted 3-min
  point count surveys at 1,513 points along 84
  routes (located primarily in pine and pine-oak
  woodlands) in the Chiricahua, Huachuca, Santa
  Catalina, Rincon, Santa Rita, Pinaleno, Galiuro,
  and Santa Teresa mountains (Fig. 1).
• We quantified burn severity within 100 m of each
  survey point using a burn severity index (BSI
  Fig. 3). Based on available fire history data,
  we estimated median time since fire for the
  majority of the burned survey points.
• We collapsed BSI values into 3 general
• categories to increase power of statistical
  tests
• 1) no evidence of fire (BSI 0)
• 2) evidence of less-severe fire (BSI 1-2)
• 3) evidence of severe fire (BSI 3-4)
• To test for associations between birds and
  recent fire, we used 1) logistic regression to
  examine whether bird presence/absence was
  associated with burn severity for 65 bird
  species, and 2) ordinal logistic regression to
  examine whether bird relative abundance was
  associated with burn severity for a subset of 16
  bird species.

Strong, positive association (P 0.05
and odds ratio 3.0) Positive
association (P 0.10 and odds ratio 1.5-3.0)
-- Strong, negative association (P
0.05 and odds ratio 0.3) -
Negative association (P 0.10 and odds ratio
0.3-0.6) 0 No observed association.

• Conclusions
• Most (73) of the species analyzed were
  positively associated with recently burned areas
  and displayed stronger associations (i.e., more
  extreme odds ratios) with survey points that had
  evidence of severe as opposed to less-severe
  fire.
• Positive associations were particularly strong
  for western wood-pewee and house wren and
  negative associations were particularly strong
  for warbling vireo and red-breasted nuthatch.
• None of the 16 species identified by Marshall
  (1963) as open-woodland birds showed positive
  associations with burned areas.
• Our results suggest that recent fires have had a
  positive effect on the distribution/relative
  abundance of several montane forest bird species
  in the region. However, these species are not the
  open-woodland birds we would have expected to
  have benefited from fire based on research by
  Marshall (1967, 1963).
• Because some bird species appear to respond
  differently to different levels of burn severity,
  future studies should examine how birds respond
  to fire across a range of burn severities instead
  of examining simple responses of birds to fire
  per se.

Literature Cited Marshall, J. T. Jr. 1957.
Birds of pine-oak woodland in southern Arizona
and adjacent Mexico. Pacific Coast Avifauna
Number 32. Marshall, J. T. Jr. 1963. Fire and
birds in the mountains of southern Arizona.
Proceedings of the Tall Timbers Fire Ecol. Conf.
2135-141.