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The Esmeraldas Woodstar (Chaetocercus berlepschi) is a poorly known and endangered hummingbird endemic to lowland and foothill moist forest in coastal western Ecuador. We encountered 11 new localities, observed two copulations, and found 26 nests of the species from October 2007 to April 2008. We observed the generally accepted descriptions of the female must have come from mis-labeled specimens of juvenile males and were incorrect. We collected the first three confirmed females of the species and describe their characteristics. The correct identification of female C. berlepschi and recognition of the species' breeding habitat should facilitate more effective conservation of the species.
The poorly known Cloud-forest Screech Owl (Megascops marshalli) is a Peruvian endemic known from only two localities, and its vocalizations have not been documented. We report the first Bolivian specimen and sound-recordings, an analysis of the species' longsong in comparison with other brown-eyed Andean screech owls, and discuss its distribution, natural history, ecological relationships with sympatric congeners, and conservation status. Longsongs were most similar to those of the allopatric Cinnamon Screech Owl (M. petersoni) in northern Peru and Ecuador. Principal component analysis of four vocal characters identified: (1) notable overlap between the two species; (2) some overlap of the Cloud-forest Screech Owl with Ecuadorian, but not with sympatric Bolivian populations of the Rufescent Screech Owl (M. ingens); and (3) considerable, evidently clinal geographic variation in the Rufescent Screech Owl. Divergence in vocal characteristics between the Cloud-forest Screech Owl in Bolivia and other species decreased with increasing geographic distance. The Cloud-forest Screech Owl is now known from six localities from Departamento Pasco, Peru, south to Departamento Cochabamba, Bolivia, and has a disjunct distribution with four subpopulations and an overall extent of occurrence of ∼12,700 km2. Its preferred habitat is pristine to at most slightly disturbed wet montane forest with high structural complexity, dense understory, and abundant epiphytes. It has been recorded at altitudes of 1,550–2,580 m, but locally its altitudinal range is ∼500 m, where it is narrowly syntopic with Rufescent Screech Owl at its lower and White-throated Screech Owl (M. albogularis) at its upper terminus. Narrowly overlapping altitudinal replacement in Andean Megascops taxa combined with variable location of replacement zones depending on local ecoclimatic conditions suggest that species' distributions are primarily maintained by exclusion via interspecific competition. The Cloud-forest Screech Owl is currently properly listed as Near Threatened, but further research may show it is more appropriately categorized as Vulnerable.
We used principal coordinates analysis to analyze variation in 11 plumage characteristics of 1,722 Savannah Sparrows (Passerculus sandwichensis) breeding at 55 different sites from throughout the species' range in Canada, Mexico, and the United States. There is clinal interpopulational variation in size with considerable overlap among localities. Savannah Sparrows resident along the Pacific coast of southern California and Baja California, and those from along the coast of Sinaloa and Sonora (i.e., saltmarsh Savannah Sparrows) differ from those throughout the rest of their range (i.e., non-saltmarsh). Variation among populations of non-saltmarsh Savannah Sparrows was clinal with the exception of those from Sable Island, Nova Scotia, which are consistently more pallid than birds from the adjacent mainland. Western Savannah Sparrows are more pallid than those in the east. The median crown stripe of eastern Savannah Sparrows is distinct, whereas the median crown stripe of western Savannah Sparrows generally is indistinct or narrow. Savannah Sparrows, with the exception of those on Sable Island, are also more pallid in relatively hot and dry areas than in cool mesic sites, following the general prediction of Gloger's Rule. There is clinal variation of saltmarsh populations along the Pacific coast with those in the north being relatively dark in coloration, and with more yellow in the supercilium than those farther south. There is also clinal variation among the populations from the east coast of the Gulf of California with pallid birds in the north, where vegetation is sparse, and darker birds to the south; these coastal birds have indistinct median crown stripes and little yellow in the supercilium.
Chickadee songs were recorded in 1997–2000 at 185 sites in 15 Illinois counties to map the distributions of song types of Black-capped (Poecile atricapillus) and Carolina chickadees (P. carolinensis). These species are parapatrically distributed from New Jersey to Kansas. Hybrid zones form in areas of sympatry and chickadees in these areas frequently exhibit unusual (i.e., aberrant) singing behaviors. The presence of aberrant vocalizations and/or the co-occurrence of the two species' song types at a site or by a single individual were considered evidence of a hybrid zone. Four hybrid zones were detected in Illinois along the range interface of these species. A comparison of the distributions of Black-capped, Carolina, and aberrant song types from this and a previous study conducted in Illinois in 1954–59 revealed little change has occurred in the distributions of these two species' song types. This overall stability of song type distributions indicates the northward movement of hybrid zones seen at other locations has probably not occurred in Illinois.
Cerulean Warblers (Dendroica cerulea) were recorded throughout the 2005–2006 breeding seasons in southern Indiana; 18 song variables were measured and compared between paired and unpaired males. The best logistic regression model for predicting pairing status included song rates and minimum frequency measures of the second section of a male Cerulean Warbler song. Unpaired males had higher song rates and higher minimum frequencies. On average, unpaired males (n = 12) sang 7.4 songs/min while paired males sang 6.4 songs/min (n = 19). Average minimum frequency was 4.0 kHz for an unpaired male and 3.5 kHz for a paired male counterpart. Female and fledgling call notes were recorded during the latter part of both breeding seasons, and quantitatively analyzed. Female chip notes (n = 4 females) had a frequency range of 4.4–8.0 kHz. Two behaviors positively identified during these vocalizations included foraging and response to a mate. Average frequency range of fledgling begging notes (n = 4 fledglings) was 5.9–7.8 kHz. Begging was the only behavior identified with these particular vocalizations. These analyses offer further understanding of intraspecific call functions and repertoire in this species.
We assessed song rates among male Cerulean Warblers (Dendroica cerulea) in Ozark riparian forest in southeastern Missouri to characterize song rate variation and estimate how many males may be missed during censuses. Average (± SD) songs per 5-min intervals for continuous 4-hr observation periods varied from 3.1 ± 4.8 (mated males) to 36.0 ± 18.7 (unmated males; n = 24 males). Unmated males averaged twice the number of songs per 5-min periods than mated males. Considerable song rate variation existed even among mated males. Song rates slightly declined over the 4-hr observation period. Song rate differences between Cerulean Warblers in Ontario and southeastern Missouri suggest caution when making assumptions about breeding status based on auditory surveys. Average male Cerulean Warbler territory size (n = 20) was 0.9 ± 0.1 ha with 27 of 31 males having at least one abutting conspecific territory. All males (n = 24) were silent for 32.7 ± 21.5 and 21.8 ± 17.4% of the 5-min and 10-min periods, respectively. Unpaired males (n = 5) were silent for 2.9 ± 3.15 and 1.2 ± 1.86% and mated males (n = 19) were silent for 37.9 ± 18.8 and 25.4 ± 16.2% of the 5-min and 10-min periods, respectively. These data demonstrate that when auditory clues are used for detection, not incorporating song rate will result in significant underestimates of density.
We examined the pattern of American Redstarts (Setophaga ruticilla) migrating through and arriving in breeding areas in northern Michigan to evaluate factors that may influence arrival of redstarts. Variation in arrival schedules coincided with variation in endogenous and exogenous factors. Redstarts arrived 3 to 7 days later during a year characterized by cold temperatures and low resource abundance as compared to years in which environmental conditions during the arrival period were more benign. Further, males verified as breeding at our site arrived 2 to 4 days before breeding females while males classified as migrants preceded migrant females by 4 days. Finally, older birds preceded younger for both verified breeders (7 days) and migrants (6 days). These findings demonstrate behavioral plasticity within the constraints of optimal migration theory which places high value on early arrival in breeding areas. Our results suggest that some species of long-distance migrants may adjust spring migration rates in response to environmental conditions.
The origin of hybrid individuals is often difficult to diagnose from phenotypic characters, and many hybrids may go unrecognized because they are morphologically ambiguous or similar to one of the parental species. We describe an unusually well-characterized intergeneric hybridization event in the Parulidae, and use it to validate DNA-based diagnosis of the parental species. Three hybrid wood-warbler fledglings resulting from a cross between a male Black-and-white Warbler (Mniotilta varia) and a female Yellow-rumped Warbler (Dendroica coronata) were discovered in 2000 in the Montréal Biodôme free-flight aviary. This is the first time these two species have been known to hybridize. Two individuals died as fledglings, whereas one remains alive in the Biodôme at present, providing an unusual opportunity to describe the plumage phenotype of a hybrid wood-warbler across age classes and the complete annual molt cycle. Diagnosis of this hybrid would have been difficult using traditional methods, as its plumage appears to be a slightly aberrant Mniotilta, whereas it is intermediate between the parental species in mensural and song characters. We compared the sequences of both mitochondrial DNA and nuclear-encoded intron loci to a comprehensive data base from nearly all Parulidae and confirmed the hybrid's parental species.
We examined the effect of habitat fragmentation, as well as breeding density and synchrony, on realized reproductive success of male Least Flycatchers (Empidonax minimus). Both breeding density and synchrony were similar in both continuous (6.75 males/ha, 3.40; respectively) and fragmented (4.04 males/ha, 2.11; respectively) habitats, and no morphological or territorial variables differed between males in either habitat. The number of nests containing extra-pair offspring was lower in fragmented habitat (11%) compared to the continuous habitat (50%). Males in fragmented habitat attracted secondary mates significantly more often than males in continuous habitat (44%, 0%; respectively) resulting in similar estimates of realized reproductive success in either habitat. Although habitat fragmentation does not appear to affect realized reproductive success of male Least Flycatchers, we suggest that males of this species demonstrate a facultative shift in reproductive tactics.
Birds behave as if clear and reflective glass and plastic windows are invisible, and annual avian mortality from collisions is estimated in the billions worldwide. Outdoor flight cage and field experiments were used to evaluate different methods to prevent collisions between birds and windows. Stripe and grid patterns of clear UV-reflecting and UV-absorbing window coverings presented an effective warning that birds avoid while offering little or no obstructed view for humans. Birds used UV-reflected signals to avoid space occupied by clear and reflective sheet glass and plastic. Window coverings with effective UV-reflecting and UV-absorbing patterns as warning signals can prevent unintentional killing of birds from collisions with windows. One-way films that made the outer surface of windows opaque or translucent were successful in deterring bird strikes. Ceramic frit glass consisting of a visual pattern of densely spaced 0.32-cm diameter dots, 0.32 cm apart was an effective collision deterrent. Uniformly covering windows with decals or other objects that are separated by 5 to 10 cm was completely or near-completely effective in preventing strikes. Twice the number of window strikes occurred at non-reflective sheet glass compared to conventional clear panes. Continuous monitoring of windows revealed one in four bird strikes left no evidence of a collision after 24 hrs and, without continuous monitoring, 25% of bird strikes were undetected.
I evaluated the effects of habitat composition on Lesser-Prairie-Chicken (Tympanuchus pallidicinctus) breeding season habitat use in shinnery oak (Quercus havardii)-dominated rangelands. Female Lesser Prairie-Chickens selected nest sites with greater visual obstruction, shrub height, shrub cover, and litter compared to adjacent rangeland sites with most (n = 21) selecting nest sites within 1 km of the leks on which they were captured. Successful nests were in areas with greater visual obstruction and were characterized by greater canopy cover of shrubs than at unsuccessful nests. Nesting habitat did not appear to be limited on the study area and use of shinnery oak-dominated rangelands did not reflect poor or scarce nesting habitat. Management that protects both the shrub and herbaceous component of the shinnery oak community is essential for maintaining nesting habitat for Lesser Prairie-Chickens in east-central New Mexico.
We studied Rock Sandpiper (Calidris ptilocnemis) breeding behavior and monitored reproductive success from 1998 to 2005 on the Yukon-Kuskokwim River Delta, Alaska, USA. We banded 24 adults and monitored 45 nests. Annual return rate of adults ranged between 67 and 100%. Six pairs of Rock Sandpipers bred at our study site for ≥2 years, and among these we did not observe mate change (i.e., when both members of a pair returned and each mated with a new individual). Nests were typically initiated by mid-May and 53% of females laid second clutches if first clutches were lost through mid-June. Males regularly incubated clutches during the morning (0800–1259 hrs AKDT) and afternoon (1300–1759 hrs) and rarely during the evening (1800– 2300 hrs), whereas female incubation was relatively consistent throughout the day. Apparent nest success (percent of known nests successfully hatching >1 chick) among first and second nests was 19 and 44%, respectively (n = 45). A minimum of 44% of hatching nests fledged at least one young. Males cared for young but half of females deserted mate and brood 1–7 days post-hatch. This first description of North American Rock Sandpiper breeding behavior from a color-marked population complements previous work on this species on the Chukotsky Peninsula, Russia.
The core of eastern White-winged Dove (Zenaida asiatica asiatica) breeding habitat historically occurred in northern México and southern Texas. Much nesting-habitat loss has occurred in this region since the mid-1900s and several large nesting colonies of the historic complex have disappeared with others currently at risk. Little knowledge exists regarding the precise location of these colonies or their current status. We reviewed the literature, interviewed biologists, and conducted site visits to Tamaulipas, México during May– August 2004 and 2005 to construct a historical account of White-winged Dove colonies. We found references to 77 possible nesting colonies thought to exist over a 50-year period in Tamaulipas. However, 26 references represented alternative names for the same colonies resulting in 51 colonies. We located 31 of these colonies of which 13 were active and 18 were inactive. The remaining 20 were not described in sufficient detail to locate. Brush clearing was listed as a cause for 78% of the 18 inactive colonies followed by weather catastrophes (56%) and overharvest (39%). Collectively, these 3 factors appeared to be responsible for 94% of all colony loss. The historic, large colonies of the past are gone and likely will not return because of these factors, primarily because of brush clearing.
We studied Sedge Wrens (Cistothorus platensis) along transects in fens of Lake Saint-François National Wildlife Area (NWA) to identify key habitat components associated with breeding territories. Stations (0.13-ha circles centered on clusters of locations) occupied by Sedge Wrens had higher lateral visibility (lower vertical cover) and lower shrub cover (lower tall shrub density, fewer shrub stands, reduced length of stands along transects, and greater distance to the nearest shrub) compared to unoccupied stations. Mean lateral visibility was low (<25%) below 100 cm and did not differ between stations, and visibility was greater for higher height classes at stations occupied by wrens. The relative cover of dominant plant species (Carex lacustris, C. aquatilis, Lythrum salicaria, Thelypteris palustris, Calamagrostis canadensis) did not vary between stations occupied or unoccupied by Sedge Wrens. The habitat structure at the territory scale influenced Sedge Wren occupancy as birds preferred stations with lower shrub cover and higher lateral visibility. We found an average of 0.21 Sedge Wrens/ha along transects, similar to densities reported in some regions of the midwestern USA.
Prescribed fire is used extensively to manage breeding habitat for Bachman's Sparrow (Aimophila aestivalis), but little is known about the effects of prescribed fire on winter habitat requirements. We used conspecific recordings in conjunction with point counts to assess relationships between winter sparrow abundance and use of prescribed fire. Counts of sparrows conducted over three winters were higher (0.59 ± 0.42) (x̄ ± SD) when surrounding vegetation was burned the previous breeding season than in areas burned >18 months earlier (0.27 ± 0.38). Year-to-year abundance estimates for individual stations increased an average of 0.39 (± 0.54) individuals per count when surrounding vegetation was burned the previous breeding season and decreased 0.22 (± 0.59) individuals per count when vegetation was not burned. Sparrow counts were positively correlated with percent bare ground cover surrounding census stations and negatively correlated with increases in percent grass cover, grass standing crop, height of grass, and shrubs <1 m in height. Prescribed fire may improve winter foraging conditions for this ground-dwelling species by reducing dense grass cover at ground level. Increased flowering responses that many dominant plants exhibit following burns also may improve winter food resources. We observed color-marked birds (n = 18) in the same areas used during the breeding season and confirmed the maintenance of year-round home ranges by some individuals.
Wildlife biologists have provided supplemental food during winter to improve post-release survival of Wild Turkeys (Meleagris gallopavo) transplanted north of their ancestral range in Minnesota. We evaluated the effectiveness of this action by monitoring overwinter and annual survival of 140 transplanted turkeys on three supplemental food and three control study areas in 2004 and 2005. Both winters of study were mild relative to historic snowfall levels and temperature. Patterns of mortality during winter were consistent across years with most mortalities occurring on control study sites. Turkeys that had been released in the prior year and survived until January of the current year had little mortality, regardless of supplemental food. The relative risk of death estimated from proportional hazards models for turkeys at supplemental food sites relative to those at control sites during winter was 5.0 in 2004 and 9.7 in 2005. Estimates of relative risk for newly released relative to experienced turkeys during winter were 9.4 in 2004 and 12.6 in 2005. Site-to-site variability in risk decreased during the non-winter period with treatment and control sites having more similar risk levels. Ninety-one turkeys died and mammalian predation was the most common cause of known mortality.
We studied the diet of 20 Barn Owl (Tyto alba) pairs breeding in three habitats (alfalfa fields, date plantations, and villages) in the same agricultural region in the Jordan Valley, Israel. Small mammals, particularly three rodents (Levant voles [Microtus socialis guentheri], house mouse [Mus sp.], and Tristram's jird [Meriones tristrami tristrami]), comprised 73 to 88% of the 3,544 prey items taken by Barn Owls in the three habitats. Frequencies in number and biomass of the rodent species differed among habitats. The number of bird species, their frequencies, and biomass in the diet were higher in villages than in the other two habitats, and were related to the higher diversity of birds breeding in villages. The frequency of birds in the diet was negatively correlated with distance from the village to open fields. Differences in the diet of Barn Owls among the three habitats most likely reflected differences in the distribution and abundance of the prey items in each habitat.
The Military Macaw (Ara militaris) is an endangered species with a fragmented distribution and declining populations. Their diet has not been described in detail but the species is considered to be a specialized granivore, and individuals may make seasonal movements in search of food resources. This study examined the diet of Military Macaws in tropical dry and oak (Quercus spp.) forests of Cuicatlán, México. We followed macaws to identify diet composition, and quantified the nutritional content of all items which they consumed. Military Macaws used 10 plant species during the year having a standardized Levin´s niche breath index of B = 0.18. Their diet consisted principally of seeds but also included fruits, leaves, and latex. Foods rich in protein and lipids composed the diet of macaws, especially during the breeding season. Macaws preferred some plant species using them more than predicted by their abundances. Food resources must be considered when managing and preserving habitat to protect this endangered species.
The foot waggle behavior in Common Loons (Gavia immer) has been postulated to serve primarily as a comfort movement, but may also have a role in thermoregulation. I studied foot waggles in Common Loons during 1994–1996. Foot waggling was most often associated with preening and resting behaviors (81.1%). They were observed also during agonistic encounters with conspecifics, in response to human disturbance (boating), and during social gatherings with other loons. Foot waggle frequency was compared to wind speed, ambient temperature, water temperature, and incident light levels. Wind speed had a negative effect and incident light had a positive effect on adult loon foot waggle frequency. Ambient air temperature and water temperature had no effect on the frequency of foot waggling. Adult loons with young foot waggled 4–5 times more per day during July–August than in May–June, when they were without young. The data suggest the loon foot waggle is primarily a comfort movement, but may also be indirectly involved in attempts by individuals to thermoregulate.
We studied variation in detection probabilities of several marsh bird species during the breeding season in relation to tidal height (i.e., water level) within several tidal marshes of the northern Gulf of Mexico. Specifically, we examined the influence of tidal height on our ability to detect Clapper Rail (Rallus longirostris), Seaside Sparrow (Ammodramus maritimus), Marsh Wren (Cistothorus palustris), Purple Gallinule (Porphyrio martinica), and Common Moorhen (Gallinula chloropus). Detection of Clapper Rails and Seaside Sparrows increased relative to tidal height while detection of Marsh Wrens decreased. Our results suggest that tidal height influences detection of specific marsh bird species, although these effects may differ geographically. We advocate including collection of tidal height information as a part of the survey protocol for effective monitoring of marsh bird populations.
The literature regarding the seet call of the American Robin (Turdus migratorius) is unclear as anecdotal accounts indicate it is an aerial alarm. A more recent, comprehensive account indicates it is most likely a contact call. We examined the meaning of seet calls through observations and a playback experiment, both of which support the aerial alarm function of the call. Robins only gave seet calls to aerial predators and many engaged in skygazing, a behavior previously unreported for robins. Robins engaged in three anti-predator behaviors, skygazing, alert, and scanning for significantly more time after hearing an alarm compared to hearing a control. American Robins, like many other birds, probably evolved this call to avoid detection by aerial predators and to warn conspecifics.
Least Flycatchers (Empidonax minimus) are socially monogamous birds that exhibit clustered nesting behavior. We examined the potential influence of forest structure in habitat selection, and formation of Least Flycatcher clusters within a habitat type not previously studied in this species: red pine (Pinus resinosa) plantations. We documented 10% less understory vegetation, 13% greater canopy cover, and 30% more deciduous trees in occupied than in adjacent, unoccupied, yet available habitat in 12 clusters in pine plantations. Well developed canopy cover and deciduous foliage appear to provide visual cues for Least Flycatchers when selecting habitat for breeding.
We monitored 124 female Golden-cheeked Warblers (Dendroica chrysoparia) at 133 nests with video cameras from 1997–2002 and 2005– 2006 at two study areas in central Texas, USA. Six adult females were depredated by snakes in 781 camera-monitored intervals when females were on the nest at night and exposed to possible nocturnal predation. Daily nest survival was 0.971 (95% CI: 0.959–0.980) and daily adult female predation while nesting was 0.008 (95% CI: 0.003–0.017). We estimated that 14.6% of breeding females were depredated on the nest during the breeding season based on the observed survival rates and assuming females whose first nest was unsuccessful and which survived attempted a second nesting attempt. Females were captured 75% of the times they were on the nest at the time of a nocturnal nest predation by a snake. Predation of nesting females is potentially an important source of mortality for Golden-cheeked Warblers, and warrants further investigation.
Black-throated Blue Warblers (Dendroica caerulescens) are subject to nest predation by a variety of avian and mammalian species. I present evidence that slugs (Gastropoda: Mollusca) can also function as nest predators. On two occasions, slugs were observed feeding on 6–7 day-old nestling Black-throated Blue Warblers at Hubbard Brook Experimental Forest, New Hampshire, USA. This is apparently the first report documenting that slugs can function as avian nest predators.
Mixed-clutch nest sharing was observed between an American Robin (Turdus migratorius) and a Northern Cardinal (Cardinalis cardinalis) in Saylor Township, Polk County, Iowa in May 2007. The nest contained three American Robin eggs and two Northern Cardinal eggs, but only American Robin young were fledged successfully. This was not a case of brood parasitism, as both females were observed alternating incubation of the nest. Competition for desirable nest sites might be a possible cause for this type of interspecific behavior.
Misdirected parental care, or care directed toward unrelated young, has been recorded for many bird species. The Wood Thrush (Hylocichla mustelina) is not known to practice this behavior or allow other species to attend to its young. We observed a Wood Thrush nest with three Wood Thrush nestlings and one Brown-headed Cowbird (Molothrus ater) nestling being attended by a male Eastern Towhee (Pipilo erythrophthalmus). The towhee fed the young of both species in the nest for at least 5 days and was subsequently observed feeding a Wood Thrush fledgling. The towhee also participated in nest maintenance and defense. The proximate cause of towhee attendance at the Wood Thrush nest remains unknown, but begging calls from the nestlings may have stimulated the behavior.
We examined King Eider (Somateria spectabilis) brood survival in the Kuparak oil field in northern Alaska in 2002 and 2003 by monitoring hens with broods using radiotelemetry. We observed complete brood loss in eight of 10 broods. Broods survived less than 2 weeks on average, and most mortality occurred within 10 days of hatch. Distance hens traveled overland did not affect brood survival. Apparent King Eider brood survival in our study area was lower than reported for eider species in other areas. We recommend future studies examine if higher densities of predators in oil fields reduces King Eider duckling survival.
We examined diet composition of Wilson's Snipe (Gallinago delicata) (n = 372) collected along the central Gulf Coast of Texas based solely on upper digestive tract contents. Food items included 11 invertebrate orders, one invertebrate class, and eight plant genera. Oligochaetes were the predominant food throughout the non-breeding period, but snipe consumed fewer (P = 0.021) earthworms in spring than in fall. Aquatic insects were frequently consumed by snipe and during spring represented approximately the same proportion of the diet as earthworms. Plant foods consisted almost entirely of seeds and comprised 9.7–26.8% of the diet throughout the non-breeding period. Wilson's Snipe consumed dipteran larvae more often during spring than fall (P = 0.056). Female snipe consumed crustaceans during spring (14.8%), while only trace amounts were found in the diet of male snipe. Differences in the diet of Wilson's Snipe between males and females were probably related to differences in habitat use as well as availability of invertebrates throughout the non-breeding period.
We used data collected during 1995– 2007 at the only Wildlife Rehabilitation Center on Tenerife Island (Canary Islands) to quantify entanglement mortality of owls. At least 66 of 1,206 Long-eared (Asio otus) and 5 of 231 Barn (Tyto alba) owls admitted to the Wildlife Rehabilitation Center were entangled in burr bristlegrass (Setaria adhaerens). Twelve (18.2%) of the 66 Long-eared Owls died as a result of entanglement while one of five Barn Owls died. A higher incidence of entanglement occurred during summer, coinciding with seed-head ripening and dispersing recently-fledged owls. Velvety plumage may be an important cost for owls, and responsible for owls acting as seed dispersers.
We monitored provisioning behavior at 18 Bobolink (Dolichonyx oryzivorus) nests during 240.5 min of videotape data from June to July 2006, and observed 64 nest visits by adults while nestlings were fitted with neck ligatures. Adults pecked or pulled at the ligatures, often aggressively, at 72% of nests (n = 18) and 52% of visits (n = 64). These behavioral responses by adults indicate the neck ligature technique is more invasive than previously believed. We documented no mortality as a result of ligature placement, but researchers should minimize the time that ligatures are in place to reduce stress to both parents and nestlings.