Cerulean Warbler Species Account

5. Species Accounts

5.32. Cerulean Warbler Species Account

USFWS Region 3 status: conservation concern AOU number: 6580

AOU abbreviation: CERW

SUMMARY

T

otal vulnerability for Cerulean Warbler was moderate, scoring 2.9 out of 5.0. The adaptive capacity category was one of the largest contributors, which was driven by a combination of factors including, a high degree of breeding site fidelity, very highly specialized habitat needs during the non-breeding season, and a fairly long distance migration. The Cerulean Warbler’s use of large mature forests was compounded by the vulnerability of this habitat to disturbance due to climate change, contributing to the indirect effects subscore. However, other factors (e.g. low vulnerability for temperate deciduous forest in general and for tropical humid forests) ultimately helped to reduce the indirect effects subscore.

Unfortunately, we had no information on non-breeding diet, which limited our ability to assess both the adaptive capacity and indirect effects categories. More data are needed for a more comprehensive understanding of Cerulean Warbler vulnerability, and winter

research should be a priority. Temperature increases and drying on the UMGL breeding grounds were other big contributors to the overall vulnerability score (Figure 5.91), partly because Cerulean Warblers are particularly sensitivity to climate change during this time of year. Climate changes on the non-breeding grounds had less effect on vulnerability. We had very little connectivity information on Cerulean Warblers from banding data, including no breeding to non-breeding encounters originating from the UMGL (Figure 5.92). However, stable isotope research from Jones et al. (2008) suggests weak connectivity between parts of the UMGL region (namely, southern Ontario) and both northern and southern portions of the non-breeding range. Although other locations in the UMGL region were not investigated, it appears that the entire non-breeding range is used by at least one Cerulean Warbler population in the UMGL. More research on migratory connectivity will continue to fill in the gaps and complete our understanding for populations from other areas.

VULNERABILITY SCORES

Total Vulnerability

Breeding climate effect

subscore NB climate effect

subscore Adaptive

capacity subscore

Indirect effects subscore

Background subscorerisk Temperature

change Moisture

change Temperature

change Moisture change

2.9 4.0 3.2 2.4 0 4.0 2.3 2.8

(maximum score of 5 for all columns)

0 1 2 3 4 5

Temperature

Moisture

Climate exposure × sensitivity score Breeding Non-breeding

Figure 5.91. Cerulean Warbler subscores for climate exposure

× sensitivity, breeding (Jun – Aug) and non-breeding regions (Dec – Feb).

169

Figure 5.92. Cerulean Warbler banding data from USGS Bird Banding Laboratory. The entire breeding range is shown in green. There were no breeding to stationary non-breeding encounters from the UMGL.

Figure 5.93. Mid-century (2040-2069) climate exposure during winter (Dec – Feb) on the Cerulean Warbler’s non-breeding grounds (main maps) and during summer (Jun – Aug) on its breeding grounds in the Upper Midwest Great Lakes LCC (inset maps).

CLIMATE EXPOSURE

5.32. Cerulean Warbler Species Account

i. Background Risk

• Quasi-extinction risk (score = 1.0) 0 probability (95% CI = 0, 0)

• Range size (score = 3.0) breeding = 1,234,266 km2; non-breeding = 971,392 km2

• PIF threats (score = 4.3): breeding score = 4.3; non-breeding score = 4.0

• Breeding PIF conservation (score = 3.6)

• Non-breeding PIF conser-

vation (score = 3.8)

ii. Adaptive Capacity

• Migration strategy (score = 4.0) Long-distance migrant (mean distance = 4601 km)

• Breeding habitat niche

specialization (score = 3.5) Macro habitats deciduous forest (mature and large, but may also use second-growth forest); nesting micro habitat tree mid-canopy to canopy (9-18 m high)

• Breeding diet niche spe-

cialization (score = 3.5) Arthropods; captured by gleaning foliage in the forest mid- and upper canopies

• Breeding site fidelity (score = 5.0) High (evidence of high fidelity but sample sizes are small)

• Non-breeding habitat

niche specialization (score = 5.0) Broadleaf/evergreen forest (though it’s possible they may use some woodland habitat also)

• Non-breeding diet niche

specialization (score = unknown) No data iii. Climate Sensitivity

• Breeding thermal range (score = 4.0) 7.0° C

• Breeding precipitation

range (score = 5.0) 10 cm

• Non-breeding thermal

range (score = 2.0) 14.5° C

• Non-breeding precipitation

range (score = 2.5) 88 cm

iv. Climate Exposure (mid-century predictions)

• Summer (Jun – Aug)

UMGL temperature (score = 4.0) 3.0° C increase

• Summer (Jun – Aug)

UMGL moisture (score = 2.0) 5.7% drier

• Winter (Dec – Feb)

non-breeding temperature S. America (score = 3.0) 2.0° C increase

• Winter (Dec – Feb)

non-breeding moisture S. America (score = 0) 2.0% drier v. Indirect Effects

• Breeding habitat vulner-

ability (score = 3.0) Some vulnerability of deciduous forest, particularly in the southeastern USA, though northern forests may expand range (USFS 2013); coverage of large mature forest expected to de- crease overall due to increased fire and pests while second-growth forests will increase (USFS 2013)

• Breeding biotic interaction

vulnerability (score = 3.0) Vulnerability of arthropods in general is largely unknown, but there may be some for na- tive species (Chown et al. 2007); small mammalian nest predators are another potential biotic interac- tion, and these may increase in abundance with climate change, especially in warm temperate regions (Karl et al. 2009, Johnston et al. 2012, Korpela et al. 2013)

• Non-breeding habitat

vulnerability (score = 1.0) Vulnerability of broadleaf tropical forest may depend on location and forest type—lowland forests may be stable because of high heat tolerance (Mahi et al. 2008, Gonzalez et al. 2010, Hunting- ford et al. 2013); very little vulnerability of woodlands and dry scrub forest, which may increase in area (Khatun et al. 2013); no vulnerability of urban areas

• Non-breeding biotic inter-

action vulnerability (score = unknown) No data

USFWS Region 3 status: common AOU number: 6520

AOU abbreviation: YEWA

SUMMARY

T

otal vulnerability for Yellow Warbler was moderate, scoring 2.2 out of 5.0. Drying on the Mexican non-breeding grounds (exposure × sensitivity) was the largest contributor. The adaptive capacity category also had a high score, which was driven by a high degree of breeding site fidelity and a fairly specialized breeding season diet. Unfortunately, we had no information on non-breeding diet, which limited our ability to assess both the adaptive capacity and indirect effects categories. More data are needed for a more comprehensive understanding of Yellow Warbler vulnerability, and winter research should be a priority. Temperature increases on the UMGL breeding grounds was not expected to have an effect on vulnerability (Figure 5.94), mostly because Yellow Warblers were not particularly sensitive to temperature change during the summer. They were sensitive, however, to temperature change during the rest of the year and to moisture changes throughout the year. Background risk had a low score, suggesting that climate change factors may be a priority for this species. We had very little connectivity information on Yellow Warblers from banding data, including no breeding to non-breeding encounters originating from the UMGL (Figure 5.95). However, stable isotope research from Boulet et al. (2006) suggests weak connectivity between the UMGL and most of the non-breeding range: breeding populations from the northeastern USA (including the UMGL region) winter in Venezuela (64%), Panama (15%), and the Yucatan (21%). We found no evidence indicating that birds winter in the Caribbean or western

Mexico, and we excluded those regions from our analyses. We focused on the Gulf of Mexico (including the Yucatan Peninsula), C. America, and S. America. More research on migratory connectivity will help to corroborate these data and fill in gaps to complete our understanding of year-round conservation priorities.

VULNERABILITY SCORES

Total Vulnerability

Breeding climate effect

subscore NB climate effect

subscore Adaptive

capacity subscore

Indirect effects subscore

Background subscorerisk Temperature

change Moisture

change Temperature

change Moisture change

2.2 0 2.4 2.4 1.6 3.0 2.7 1.5

(maximum score of 5 for all columns)

*

*

*

0 1 2 3 4 5

UMGL

Mexico

C. America

S. America

Temperature exposure × sensitivity score Breeding Non-breeding

*

0 1 2 3 4 5

UMGL

Mexico

C. America

S. America

Moisture exposure × sensitivity score Breeding Non-breeding

Figure 5.94. Yellow Warbler subscores for climate exposure × sensitivity, breeding (Jun – Aug) and non-breeding regions (Dec – Feb). *Non-breeding score ≥ 20%

greater than breeding.