Environmental noise influences song frequency of Yellow Warblers (Dendroica petechia) in Grand Teton National Park

We explored how Yellow Warblers (Dendroica petechia) alter their songs when encountering noise in Grand Teton National Park. Different strategies for avoiding signal masking are used by other species of birds, yet there is a lack of information of birds’ responses to higher noise levels -- above 65 dB; such levels are often found in National Parks that have many visitors. In this study, we investigated singing behavior of Yellow Warblers when facing noise that ranged from 30 dB to 80 dB. In these preliminary results, we found that some features of Yellow Warblers did not appear to change with background noise level, including mean minimum frequency, bandwidth and song length. Other song features we studied did show small but statistically significant changes with higher background noise, including the peak frequency and the mean minimum frequency, both of which were significantly negatively correlated with the level of background noise. This result is different from the positive correlations that are typically observed. We speculate that this difference is due to the very high dB levels of background noise that we observed. Featured photo by wagon16 on Flickr. https://flic.kr/p/G2W6Bk

Environmental noise influences song frequency of Yellow Warblers (Dendroica petechia) in Grand Teton National Park

We explored how Yellow Warblers (Dendroica petechia) alter their songs when encountering noise in Grand Teton National Park. Different strategies for avoiding signal masking are used by other species of birds, yet there is a lack of information of birds’ responses to higher noise levels–above 65 dB; such levels are often found in National Parks that have many visitors. In this study, we investigated singing behavior of Yellow Warblers when facing noise that ranged from 30 dB to 80 dB. In these preliminary results, we found that some features of Yellow Warblers did not appear to change with background noise level, including mean minimum frequency, bandwidth and song length. Other song features we studied did show small but statistically significant changes with higher background noise, including the peak frequency and the mean minimum frequency, both of which were significantly negatively correlated with the level of background noise. This result is different from the positive correlations that are typically observed. We speculate that this difference is due to the very high dB levels of background noise that we observed. Featured photo bywagon16 on Flickr. https://flic.kr/p/G2W6Bk

Avian population trends in Scalesia forest on Floreana Island (2004-2013): Acoustical surveys cannot detect hybrids of Darwin’s tree finches Camarhynchus spp.

SummaryFloreana Island has the highest proportion of local land bird extinctions on the Galápagos Archipelago, and is home to the range-restricted and critically endangered Medium Tree Finch Camarhynchus pauper. We used acoustic surveys during 2004, 2008 and 2013 to compare the estimated population size of C. pauper and other land bird species in a remnant patch of Scalesia forest. First, we compared song in C. pauper and C. parvulus and the recently discovered Camarhynchus hybrid group to justify our use of acoustic surveys to detect population trends given contemporary hybridisation between C. pauper and C. parvulus. Song differed significantly between C. pauper versus C. parvulus and hybrid birds, but not between C. parvulus versus hybrid birds. Second, we compared population size estimates. Camarhynchus pauper declined by 52% between 2004 and 2013 (with a 10% increase since 2008); C. parvulus/hybrid increased by 45% between 2004 and 2013 (with 28% decrease since 2008). In 2013, there were ∼ 419 C. pauper males in the Scalesia forest (estimate for Scalesia habitat only) and ∼ 2,537 males on Floreana Island (estimate for the entire available highland habitat). Not all species showed a pattern of decline in the highland Scalesia habitat between 2004 and 2013: Dendroica petechia (+256%), Crotophaga ani (+254%) Geospiza fuliginosa (+23%), and Myiarchus magnirostris (+11%) increased, while the ground finch G. fortis (-76%) decreased. Understanding why C. pauper is declining while other land bird species are increasing in the same habitat requires continued inquiry and monitoring efforts.

Are Nestlings the Cue for Reduction of the Adrenocortical Response to Stress in Male Yellow Warblers Breeding at High Latitude?

Abstract. Acute corticosterone secretion helps individuals survive perturbation, particularly when faced with unpredictable conditions. However, elevated corticosterone is often incompatible with reproduction. Male Yellow Warblers (Dendroica petechia) breeding at high latitude avoid this conflict by exhibiting a reduced adrenocortical response while provisioning nestlings. To determine if this reduction is cued by nestlings, in June 2000 we switched clutches between nest pairs to manipulate hatching date. We sampled males with early-hatching clutches for the adrenocortical response 24 hr after nestlings hatched, but 24 hr prior to the premanipulated (original) hatching date. Similarly, we sampled males with late-hatching clutches 24 hr after the original hatching date, but prior to nestlings hatching. Males with early-hatching clutches (n = 6) showed no reduced adrenocortical response, while males with late-hatching clutches (n = 6) appeared to show a reduced response even without nestlings, suggesting that nestlings do not cue the reduction. An endogenous clock, day-counting mechanism, or hormonal changes may be associated with the reduced adrenocortical response.