Yellow Warbler Nests Research Articles

Responses of Female Yellow Warblers to Playbacks Signaling Brood Parasitism or Predation Risk: A Quasi-Replication Study

Many avian species are negatively impacted by obligate avian brood parasites, which lay their eggs in the nests of host species. The yellow warbler (Setophaga petechia), which is host to the brood-parasitic brown-headed cowbird (Molothrus ater), represents one of the best-replicated study systems assessing antiparasitic host defenses. Over 15 prior studies on yellow warblers have used model-presentation experiments, whereby breeding hosts are exposed to models of brown-headed cowbirds or other nest threats, to test for anti-parasitic defenses unique to this species. Here we present results from our own quasi-replication study of the yellow warbler/brown-headed cowbird system, which used a novel design compared to previous experiments by pivoting to conduct acoustic playback treatments only, rather than presenting visual models with or without calls. We exposed active yellow warbler nests to playbacks of brown-headed cowbird chatters (brood parasite), blue jay (Cyanocitta cristata; nest predator) calls, conspecific “seet” calls (a referential alarm call for brood parasitism risk), conspecific “chip” calls (a generic alarm call), or control wood thrush (Hylocichla mustelina; harmless heterospecific) songs during the incubation stage. Similar to previous studies, we found that female yellow warblers seet called more frequently in response to playbacks of both brood parasitic chatter calls and conspecific seet calls whereas they produced more chip calls in response to the playback of nest predator calls. In contrast, female yellow warblers approached all playbacks to similar distances, which was different from the proximity patterns seen in previous studies. Our study demonstrates the importance of both replicating, and also pivoting, experimental studies on nest defense behaviors, as differences in experimental design can elicit novel behavioral response patterns in the same species.

Responses of Nesting Yellow-Headed Blackbirds and Yellow Warblers to Wrens

Abstract We studied nest defense behavior of Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and Yellow Warblers (Dendroica petechia) in response to two species of common nest destroyers. We presented freeze-dried models of Marsh Wrens (Cistothorus palustris) at Yellow-headed Blackbird nests and House Wrens (Troglodytes aedon) at Yellow Warbler nests during the incubation stage. We presented a Clay-colored Sparrow (Spizella pallida) as a control for both species. Male Yellow-headed Blackbirds responded more intensively to the Marsh Wren model than the control and female blackbirds responded intensively to both models but were more aggressive toward the Marsh Wren. Most Yellow Warblers did not respond to the House Wren model with their typical predator responses (e.g., alarm calls). Some female warblers were aggressive toward the wren model, whereas others sat in their nest. Sitting in the nest as a defense to deter nest destruction by House Wren needs further investigation. Differences in respons...

Nesting Ecology of Yellow Warblers (Dendroica petechia) in Montane Chaparral Habitat in the Northern Sierra Nevada

The Yellow Warbler (Dendroica petechia) is considered a riparian specialist in much of western North America, but in California it also breeds in a second habitat type: montane chaparral of the Sierra Nevada and southern Cascades. We monitored Yellow Warbler nests in montane chaparral and assessed their poorly known nesting ecology in this habitat. We also conducted point counts in upland habitat throughout the region. We determined habitat associations for Yellow Warblers based on nest site and point-count vegetation data; nests were predominantly in bush chinquapin (Chrysolepis sempervirens) and greenleaf manzanita (Arctostaphylos patula), and point-count abundance was most strongly associated with high overall shrub cover. The importance of montane chaparral for a number of shrub-dependent Sierran birds is well documented, yet the chaparral is threatened by various practices including fire suppression, closed-canopy-focused forest management, and understory fuels-reduction treatments. Although Yellow Warblers are far more abundant in wet mountain meadow riparian habitat in the region, we recommend that management of montane chaparral habitat consider this species and the requirements of other shrub-nesting birds.

Geographic Variation in Nests of Yellow Warblers Breeding in Churchill, Manitoba, and Elgin, Ontario

Abstract. Nesting structures are important for successful reproduction in most birds, and, because of this, geographic variation in nest morphology and composition are usually interpreted as adaptations to breeding in different environments. We compared the structure of nests of Yellow Warblers (Dendroica petechia) breeding in Churchill, Manitoba, and Elgin, Ontario, Canada. Churchill is subarctic in habitat and typically much colder during the breeding season than Elgin. We compared temperature, rainfall, and wind speed at these two sites and then tested whether differences in nest structure corresponded to different environments. Yellow Warblers breeding in Churchill built larger, less porous nests that retained heat better but also absorbed more water and took longer to dry than Yellow Warbler nests from Elgin. We suggest that differences in the structure of Yellow Warbler nests represent adaptations to breeding in different environments because the differences in nest morphology and properties of heat...

Does nesting habitat predict hatch synchrony between brood parasitic brown‐headed cowbirdsMolothrus aterand two host species?

Nestling brown‐headed cowbirdsMolothrus atertypically hatch earlier and grow faster than young of the many host species of this generalist obligate brood parasite. However, a cowbird chick also benefits from the presence of some host nest mates as the parasite is provisioned disproportionately more with increasing brood size. Since asynchronous hatching affects both cowbird and host nestlings’ growth and survival, mechanisms that optimize the timing of egg‐laying by female parasites should be prevalent. Several habitat features might facilitate optimal timing of parasitic egg‐laying and we examined whether aspects of host nesting habitat predicted cowbird hatching synchrony. We tested whether synchronous nests were less concealed, closer to perches, and located in areas of higher host density than asynchronous nests using a broad‐scale information theoretic approach. There was no support for these predictions regarding song sparrow (Melospiza melodia; n=55) or yellow warbler (Dendroica petechia; n=67) nests parasitized by brown‐headed cowbirds at Mono Lake, USA. For example, the best statistical models for predicting hatching synchrony in yellow warbler nests included nesting‐patch width and nest‐substrate shrub species. However, these relationships were relatively weak: both synchronous and asynchronous nests were in patches with statistically indistinguishable widths and the two dominant shrub species at our site contained similar proportions of synchronous and asynchronous nests. We conclude that the variability of host nesting habitats does not contribute to a biologically consistent effect on hatching synchrony by this generalist brood parasite.

Influence of Mammal Activity on Nesting Success of Passerines

For many avian species, predation is the leading cause of nest failure. However, relationships between predator abundance and nest predation often differ across spatial scales. We examined the relationship between environmental characteristics in meadows and mammalian predator activity, the relationship between predator activity at 2 spatial scales, and the probability of nest predation of willow flycatchers (Empidonax traillii), dusky flycatchers (Empidonax oberholseri), and yellow warblers (Dendroica petechia) in the central Sierra Nevada Mountains, California, USA. Environmental characteristics associated with the detection of nest predators varied depending on species. Douglas's squirrel (Tamiasciurus douglasii) and chipmunks (Tamias spp.) were associated with characteristics common along edges of meadows; short-tailed weasels (Mustela erminea) were associated with willows, whereas mice (Peromyscus maniculatus, Reithrodontomys megalotis, and Microtus spp.) and long-tailed weasels (Mustela frenata) were distributed throughout the meadows. The probability of predation of willow and dusky flycatcher nests increased with increasing short-tailed weasel activity, and the probability of predation of yellow warbler nests increased with increasing activity of chipmunks and short-tailed weasels. Variation in the occurrence of predator species in different areas of the meadows likely influences the probability of nest predation by each species and the nesting success of birds. Identifying factors that influence the distribution and abundance of common nest predators will likely be integral to the development of conservation efforts to increase the reproductive success of some bird species.

Nest Success of Yellow Warblers in Willow Habitats: The Role of Surface Water and Snakes

Yellow Warblers (Dendroica petechia) are migratory songbirds found in high abundance in the tall willow (Salix boothii) habitats of Grand Teton National Park (GTNP). Willows are found in wet soils with high water tables and varying densities of exposed surface water. Dense surface area of water leads to thick, well foliated, continuous patches of S. boothii, which is the favored nesting habitat of Yellow Warblers. This water, however, also supports the favored prey base of the wandering garter snake (Thamnophis elegans vagrans), which has been known to prey on songbird nest contents when the opportunity arises. We hypothesized that nest territories containing high densities of surface water would also attract garter snakes, and increase the probability of nest failures. We found and monitored 28 Yellow Warbler nests, recorded their locations and fates (success or failure) and measured the density of surface water within each nest territory. We analyzed nest success with the logistic-exposure method coupled with comparisons of models with and without water density as an explanatory variable. Information theoretic model comparison consistently supported models with water density over those without. A significant correlation was found between water density within a nest territory and that nest's daily survival probability. The estimate of this effect was -0.049 (a logistic model parameter) with a standard error of 0.019. Expressed alternatively, each 5-meter per territory increase in waterway density decreases the odds ratio of nest survival by 21%. While water density provides a trade off between nesting habitat and predation pressure, other predation causes and temporal water density variation likely contribute to overall warbler productivity in important ways as well.

Red squirrel predation on warbling vireo and yellow warbler nests

Red squirrel predation on warbling vireo and yellow warbler nests

Predator Activity and Nest Success of Willow Flycatchers and Yellow Warblers

Willow flycatchers (Empidonax traillii) and yellow warblers (Dendroica petechia) are riparian-dependent species that have declined throughout much of their former range in California, USA. These declines have been primarily associated with the loss of riparian breeding habitat, increases in brood parasitism, and increases in nest predation. We (1) identified potential nest predators using inactive yellow warbler nests; (2) determined the relationship of meadow wetness, meadow size, and amount of edge to predator activity; (3) determined the association between potential nest predator activity and nest success; and (4) determined how proximity to forest edge and isolated trees was related to nest success. We used automatic cameras to monitor inactive yellow warbler nests baited with zebra finch (Taeniopygia guttata) eggs to identify nest predators. We used track plates (mammalian), point counts (avian), and time-constrained searches (reptilian) to assess the activity of potential nest predators. We photographed short-tailed weasel (Mustela erminea), Douglas squirrel (Tamiasciurus douglasii), lodgepole chipmunk (Tamias speciosus), deer mouse (Peromyscus maniculatus), and unidentified chipmunks (Tamias spp.) depredating yellow warbler nests baited with finch eggs. The amount of meadow covered with water was negatively associated with the activity of chipmunks and Douglas squirrels. Meadow size was negatively associated with Douglas squirrel activity. The amount of edge was positively associated with the activity of Douglas squirrels, chipmunks, Steller's jays (Cyanocitta stelleri), and brown-headed cowbirds (Molothrus ater). Nest predation was the major cause of nest failure in our study. However, only short-tailed weasels, Douglas squirrels, Clark's nutcrackers (Nucifraga columbiana), Steller's jays, Cooper's hawks (Accipiter cooperii), and brown-headed cowbirds had activity indices that were negatively associated with nest success of either species. The distance to isolated trees was associated with willow flycatcher nest success, whereas the distance to both isolated trees and to the forest edge was associated with yellow warbler nest success-nests located closer to isolated trees and the forest edge were more likely to be parasitized and/or depredated. Our results suggest that flooding portions of meadows may restrict meadow access to forest-edge-associated nest predators.

EFFECTS OF BROWN-HEADED COWBIRDS AND PREDATORS ON THE NESTING SUCCESS OF YELLOW WARBLERS IN SOUTHWEST COLORADO

We studied the effects of brood parasitism by Brown-headed Cowbirds (Molothrus ater) and predators on the reproductive biology of Yellow Warblers (Dendroica petechia) in La Plata County, Colorado, 1992–1996. Overall, 36.4% of Yellow Warbler nests (n = 66) were parasitized by Brown-headed Cowbirds. Although parasitized and nonparasitized nests were equally likely to fledge at least one warbler, in nonparasitized nests, warblers had larger clutches, hatched more young, and tended to fledge more young. Frequency of parasitism was not influenced by nest height and, on a weekly basis, was not correlated with number of warbler nests initiated. Overall, 39.1% of Yellow Warbler nests were lost to predators, but complete predation was not affected by nest height. On a weekly basis, percent complete predation of warbler nests increased with number of active nests. No significant relationship existed between frequency of complete predation and frequency of parasitism in Yellow Warbler nests.

Nestling competition, rather than supernormal stimulus, explains the success of parasitic brown-headed cowbird chicks in yellow warbler nests

Interspecific parasitic chicks are usually fed more than the smaller host young with whom they share the nest. This could be due to parasitic chicks having evolved exaggerated features that are preferred by the adults to the features present in their own young (the supernormal stimulus hypothesis). Alternatively, the success of parasitic chicks could be due to them being better competitors. We tested these hypotheses by studying the interaction between brown-headed cowbird chicks, Molothrus ater , and a common small host, the yellow warbler, Dendroica petechia . Parasitic chicks begged more intensively than the host's young and received most of the feeds. The relative height reached by the begging chicks of both species was the most important variable in determining their feeding success. Being larger and begging intensively, brown-headed cowbirds were better able to reach higher than the host's young, but at equal heights parasitic chicks were no better than the host's young at gaining feeds. It is suggested that the success of the brown-headed cowbirds when parasitizing yellow warblers is due to them physically out-competing the smaller young of their hosts, and not to them evoking a stronger response from the hosts by being a supernormal stimulus.

Removal of Yellow Warbler Eggs in Association with Cowbird Parasitism

In this study, I quantified the removal of eggs by the Brown-headed Cowbird (Molothrus ater) from parasitized Yellow Warbler (Dendroica petechia) nests. Laying cowbirds removed one warbler egg from about one in three parasitized nests. Assuming the same individual was involved in both acts, cowbirds removed host eggs on a day before or the same day they laid their own eggs (33.3%, n = 8 nests), on the same day (20.8%, n = 5) but after they laid, or on the same or subsequent days (46%, n = 11). As almost half (41%) of the parasitized nests received cowbird eggs before host eggs appeared, many cowbirds that removed eggs had to return to the nest to do so, although burial precluded that at some nests. Return trips increased the chances that a cowbird might mistakenly remove its own egg, especially if it was the only egg in the nest, and that interactions might occur between host and parasite. Explanations for the removal of eggs at the time of parasitism are summarized and two hypotheses are tested. The likelihood of warblers accepting a cowbird egg experimentally introduced into their nests was not influenced by the removal of a host egg at the time of parasitism, as predicted by the "host deception" hypothesis. Yellow Warblers tolerated five- and four-egg clutches being reduced to three eggs (36/37 nests), but abandoned nearly one-third of clutches reduced to two eggs (13/42) and most clutches reduced to one egg (20/22). Only one control nest was deserted (n = 41 and 59 clutches of five and four eggs, respectively). Only four of 13 (31%) clutches reduced to one egg of each of the warbler and cowbird were abandoned, but 11 of 14 (79%) clutches reduced to only one cowbird egg were deserted. None of the 10 clutches reduced to two cowbird eggs was deserted. These results suggest that cowbirds can remove at least two eggs without risking desertion by the warblers. It is not clear why only one egg is removed, when removal occurs in the first place. Cowbirds that manage to ingest eggs they remove undoubtedly gain nourishment.

Patterns of Shiny Cowbird Parasitism in St. Lucia and Southwestern Puerto Rico

The density of Shiny Cowbirds (Molothrus bonariensis) in lowland St. Lucia and Martinique is about six individuals/km2 compared to 49/2 in lowland southwestern Puerto Rico. Their distribution in the Antilles may be related to agriculture that provides food for adults, as much as to availability of suitable hosts. In St. Lucia, four of eight potential host species were parasitized. Black-whiskered Vireos (Vireo altiloquus) and Yellow Warblers (Dendroica petechia) accounted for 90% of all parasitized nests. Patterns of parasitism did not match host availability in either SW Puerto Rico or St. Lucia. In St. Lucia only Gray Kingbirds (Tryannus dominicensis) rejected > 75% of experimental cowbird eggs. Gray Kingbirds, Northern Mockingbirds (Mimus polyglottos), and Greater Antillean Grackles (Quiscalus niger) were rejecters in Puerto Rico. The success of parasitized Yellow Warbler nests was higher in Puerto Rico than in St. Lucia. Cowbird parasitism reduced Yellow Warbler nest success in St. Lucia, but not Puerto Rico. Comparisons with Puerto Rico indicate that neither hosts nor cowbirds in St. Lucia have evolved defenses or counter-defenses during a 40-year period.

Spatial and temporal multi-species nesting aggregations in birds as anti-parasite and anti-predator defenses

1. The purpose of this study was to determine whether the yellow warbler (Dendroica petechia) derives any benefits from nesting in close proximity to its own and other species in reducing predator pressure or the incidence of brood parasitism by the brown-headed cowbird (Molothrus ater). 2. Yellow warblers nesting synchronously with their own and with neighbouring species resulted in a proportionate reduction in the number of nests preyed upon, suggesting a ‘swamping effect’ of the local predators. A significantly lower incidence of predation occurred at yellow warbler nests which were inside a gray catbird (Dumetella carolinensis) response range. This was thought to be the result of yellow warblers taking advantage of the catbird's nest-guarding behaviour and aggressive responses to predators. 3. Yellow warblers nesting synchronously with other yellow warblers were subject to a proportionately lower incidence of brood parasitism than asynchronous nests, suggesting a ‘swamping effect’ on the cowbird. A significantly lower incidence of brood parasitism occurred at yellow warbler nests which were in a red-winged blackbird (Agelaius phoeniceus) response range. The yellow warbler was thought to be taking advantage of the aggressive response of red-winged blackbirds to cowbirds. 4. Overall, yellow warblers which nested within the response range of red-winged blackbirds or gray catbirds had significantly higher nest success than other yellow warblers. This suggests that selection for defence against predators and cowbirds may lead to multi-species aggregations.