Grey Warbler Research Articles

Breeding Bird Response to Riparian Buffer Width in Managed Pacific Northwest Douglas-Fir Forests

We examined the relative importance of riparian vs. upland habitats to breeding birds by comparing species abundance, richness, and similarity of bird communities in managed Douglas-fir forests in western Washington State, USA. We also examined whether forested buffer strips along second- and third-order streams effectively maintain the pre-logging riparian breeding bird community by comparing species abundance, richness, and turnover among three treatments: (1) unharvested controls; (2) sites that were clear-cut, leaving a narrow (∼14 m) forested buffer on both sides of the stream; and (3) sites that were clear-cut, leaving a wide (∼31 m) forested buffer along both sides of the stream. Deciduous trees, berry-producing shrubs, and other deciduous shrubs less common in adjacent upland forest characterized streamside zones. Despite different vegetation features, riparian and upland habitats did not differ in any measures of bird species richness and composition. No species or species group was more abundant in the upland. Neotropical migrants, resident species, and species associated with deciduous trees and shrubs in forested habitats were more abundant in riparian habitats than in adjacent uplands. Total bird abundance and abundance of four species (American Robin [Turdus migratorius], Pacific-slope Flycatcher [Empidonax difficilis], Black-throated Gray Warbler [Dendroica nigrescens], and Winter Wren [Troglodytes troglodytes]) were higher in riparian habitats. Abundance of these riparian associates was correlated with percent cover of berry-producing shrubs and the number of deciduous trees in the canopy. We found that the number of breeding bird species on sites with narrow buffers increased from slightly fewer than controls before harvest to an average of 10 more species than controls after harvest, a change reflected in an average 20% increase in species turnover on narrow-buffer sites relative to controls. Total bird abundance did not differ between treatments and controls. Resident species, those species associated with shrubs in forested habitats and conifer trees, declined on both buffer treatments. Species associated with upland and riparian forests (Black-throated Gray Warbler, Golden-crowned Kinglet [Regulus satrapa], and Brown Creeper [Certhia americana]) decreased in abundance on riparian buffer treatments relative to controls, whereas species associated with open, shrubby habitats (Dark-eyed Junco [Junco hyemalis], Cedar Waxwing [Bombycilla cedrorum], and Song Sparrow [Melospiza melodia]) increased in abundance on one or both riparian buffer treatments. High species turnover on narrow-buffer treatments indicated that buffers <14 m on each side of the stream did not maintain the pre-logging bird community. There was little difference in species turnover or species richness between the wide-buffer treatment and the control, indicating that a 30-m buffer on both sides of second-order and third-order streams maintains most of the pre-logging bird community in the first two years postharvest. The Black-throated Gray Warbler was the only riparian associate to decline on both the narrow- and wide-buffer treatments; its abundance was positively correlated with buffer width, and a buffer ≥45 m wide on each side of second- and third-order streams was needed to support populations at densities found on unharvested controls. To maintain the entire breeding bird community associated with forested riparian habitats in the coastal Northwest, we recommend a minimum buffer of 45 m along both sides of second- and third-order streams. Habitat features such as deciduous trees (Alnus rubra and Acer macrophyllum) and berry-producing shrubs (especially Rubus spectabilis) appear to be important and should be maintained within forested riparian buffer strips. This study documents short-term effects of riparian treatments on the breeding bird community, which may take several years to respond to habitat manipulations. Thus, we recommend continued monitoring to assess long-term effects of buffer width reduction.

Habitat Preferences of Pinyon-Juniper Specialists Near the Limit of Their Geographic Range

Abstract We investigated habitat preferences for five pinyon-juniper specialists during the 1998 and 1999 breeding seasons in Utah juniper (Juniperus osteosperma) woodlands of southwestern Wyoming. We compared avian use and availability of vegetation features using univariate and multivariate analysis to detect selection for vegetative features of pinyon-juniper specialists near the northeastern range boundary of pinyon-juniper habitat on the Colorado Plateau. Gray Flycatchers (Empidonax wrightii), Juniper Titmice (Baeolophus griseus), and Bewick's Wrens (Thryomanes bewickii) preferred woodlands with high overstory juniper cover. The Juniper Titmouse was associated with senescent trees, Blue-gray Gnatcatcher (Polioptila caerulea) with rock outcrops and shrubs in the family Rosaceae, and Black-throated Gray Warbler (Dendroica nigrescens) with pinyon pine (Pinus edulis). We suggest the geographic distribution of four of five pinyon-juniper specialists is limited by the occurrence of pinyon pine in semiarid woodlands on the northeastern Colorado Plateau. The geographic limit for Blue-gray Gnatcatchers in this region may correspond to the presence of mountain mahogany in the woodland understory. The conservation of pinyon-juniper specialists in southwestern Wyoming will benefit from the maintenance of successional processes, particularly those that perpetuate mature woodlands with a pinyon pine component.

HABITAT PREFERENCES OF PINYON-JUNIPER SPECIALISTS NEAR THE LIMIT OF THEIR GEOGRAPHIC RANGE1

Abstract We investigated habitat preferences for five pinyon-juniper specialists during the 1998 and 1999 breeding seasons in Utah juniper (Juniperus osteosperma) woodlands of southwestern Wyoming. We compared avian use and availability of vegetation features using univariate and multivariate analysis to detect selection for vegetative features of pinyon-juniper specialists near the northeastern range boundary of pinyon-juniper habitat on the Colorado Plateau. Gray Flycatchers (Empidonax wrightii), Juniper Titmice (Baeolophus griseus), and Bewick's Wrens (Thryomanes bewickii) preferred woodlands with high overstory juniper cover. The Juniper Titmouse was associated with senescent trees, Blue-gray Gnatcatcher (Polioptila caerulea) with rock outcrops and shrubs in the family Rosaceae, and Black-throated Gray Warbler (Dendroica nigrescens) with pinyon pine (Pinus edulis). We suggest the geographic distribution of four of five pinyon-juniper specialists is limited by the occurrence of pinyon pine in semiarid ...

Effects of stream size on bird community structure in coastal temperate forests of the Pacific Northwest, U.S.A.

Abstract. Vegetation and spring breeding bird populations associated with riparian forests on high and low order rivers of the Olympic peninsula, Washington (USA), were censussed in 1990 and 1991. The objectives were to (1) provide a baseline description of bird communities associated with unmanaged riparian forests, (2) determine whether there is a difference between bird communities along large and small rivers, and (3) identify what biophysical aspects of the fluvial corridor are most important in determining bird community structure. The approach was to link riparian bird community structure to river order and discuss relationships to vegetation, geomorphology and associated hydrologic disturbance regimes.Large rivers tended to have more deciduous vegetation than small rivers (P = 0.07). Deciduous vegetation and patch types appeared to be linked to river size through stream valley shape and disturbance history. Bird species richness and abundance were significantly higher (P&lt;0.05) on larger rivers (67–140 m width) than on small rivers (12–21 m width) and were positively correlated with the percentage of deciduous trees present at a site. The data suggest that migrant birds, such as the black‐throated grey warbler (Dendroica nigrescens) and warbling vireo (Vireo gilvus), require large tracts of contiguous hardwoods for successful breeding. Additionally, birds such as the Hammond's flycatcher (Empidonax hammondii) and hairy woodpecker (Picoides villosus) appear to depend on the juxtaposition of hardwoods and conifers during the breeding season. We conclude that bird communities on large rivers differ from those on small rivers and that these differences occur predictably with stream order.

The Adaptive Zone of the Genus Gerygone (Acanthizidae) as Shown by Morphology and Feeding Habits

SummaryUsing body morphology, feeding ecology and behaviour, this paper describes the adaptive zone of the species-rich Australo-Pacific genus Gerygone. Gerygone is a genus of small bodied, specialist insectivores that obtain the majority of their prey by gleaning and snatching it from the foliage. Species tend to be ecologically and morphologically similar. Evolution has mainly taken the form of specialisation to different habitats, to produce a largely allopatric assemblage of species. In this it parallels the larger bodied, foliage-gleaning Lichenostomus honeyeaters and contrasts with other species-rich endemic warbler-like genera, such as Sericornis and Acanthiza, where sympatric species exploit different substrates, forage at different heights above the ground, and use different foraging behaviours. The greatest evolutionary shifts occur in the insular species, Gerygone igata and G. albofrontata, which are morphologically and ecologically distinct from other Gerygone. On the limited data available, it appears that the morphological radiation of Gerygone in Australia and New Guinea is constrained by the abundance of other insectivorous genera.

Morphological and Vocal Variation in the Black-Throated Gray Warbler in the Pacific Northwest

Morphological and Vocal Variation in the Black-Throated Gray Warbler in the Pacific Northwest

Mixed-species flocking of forest birds on Little Barrier Island

Abstract Three aspects of mixed-species flocking of forest birds on Little Barrier Island were investigated. Whiteheads, fantails, parakeets, and grey warblers occurred more often in flocks than in “non-flocking” situations. Whiteheads were the main lead species, although parakeets formed groups within flocks and occasionally appeared to lead. Whitehead clumps defined the flock centre; only fantails were found commonly in the centre with whiteheads. Birds other than whiteheads generally orientated below or to the side of their nearest neighbours. We suggest that mixed-species flocking is a significant factor influencing the structure of forest bird communities in New Zealand during winter.

Brood‐parasitism by the Shining Cuckoo Chrysococcyx lucidus at Kaikoura, New Zealand

For three seasons starting in 1976 I studied the breeding of Shining Cuckoos Chrysococcyx lucidus in forest near Kaikoura, New Zealand. There is no evidence that the cuckoo parasitizes any host on mainland New Zealand other than the Grey Warbler Gerygone igata. A nestling cuckoo returned to within 1 km of its natal site in a subsequent breeding season, presumably after migrating beyond New Zealand. Empirical and theoretical estimates of the area occupied by Shining Cuckoos while breeding are given. Cuckoos near Kaikoura laid during ten weeks, the modal week of laying following seven weeks after the presumed peak of arrival of birds in New Zealand. First clutches of the host escaped parasitism because they were laid before most cuckoos arrived. Parasitized clutches received one cuckoo egg which replaced a host's egg. It was laid before, just after or long after the host began incubating, and mimicry was lacking. Cuckoo eggs, which were about 8% of the adult cuckoo's weight, hatched in 14–17 days. The frequency of parasitism near Kaikoura was 55% of late clutches (n = 40).At 3–7 days old, nestling Shining Cuckoos evicted from the nest all other contents. The nestling period was at least 19 days. Growth in weight followed a logistic curve and the equation is given. Just over half the cuckoo eggs produced fledglings. The effect of brood‐parasitism on the Grey Warbler's productivity was small. Only 17% of late warbler eggs, and late eggs only, were prevented by parasitism from yielding fledglings. Late laying by some Shining Cuckoos (relative to the host's incubational cycle), and late eviction, often led to brief inter‐specific competition among nestlings for food. The brief coexistence of young Warblers and Cuckoos in the nest may explain the apparent mimicry by newly‐hatched Shining Cuckoos of the host's young.

Morphometrics of forest birds in the Orongorongo Valley, Wellington, New Zealand

Abstract Birds in indigenous forest in the Orongorongo Valley, Wellington, were mist-netted from 1967 to 1976, and 3902 were weighed and measured. Average weight and measurements are given for New Zealand pigeon, shining cuckoo, long-tailed cuckoo, morepork, New Zealand kingfisher, rifleman, hedgesparrow, whitehead, grey warbler, fantail, tomtit, song thrush, blackbird, silvereye, bellbird, tui, and chaffinch. In 5 species males and females were easily identifiable by plumage differences, and also differed in size. Whiteheads were sometimes mis-sexed on the basis of head colour. Tui were not sexually dichromatic, but were strongly dimorphic, and were sexed by weight and wing length. Principal component analysis of measurements of tui and whitehead each produced 2 clusters of points that were assumed to represent males and females. The clusters for tui agreed with the identification derived from weight and wing length. Some Whiteheads classified as females from plumage were classified as males by principal...

The Grey Warbler's Care of Nestlings: A Comparison Between Unparasitised Broods and those Comprising a Shining Bronze-Cuckoo

SUMMARYGILL, B.J. 1982 The Grey Warbler's care of nestlings: a comparison between unparasitised broods and those comprising a Shining Bronze-Cuckoo. Emu 82: 177–181.Grey Warblers Gerygone igata at Kaikoura, New Zealand, raised either a brood of up to four of their own young or one nestling Shining Bronze-Cuckoo Chrysococcyx lucidus. The Cuckoo never weighed as much as four nestling Warblers of the same age, was visited with food less often than three or four Warblers, and had fewer faecal sacs removed. Therefore raising a Cuckoo to fledging required less effort in terms of feeding-visits and hygiene than raising a brood of several Warblers. Single Cuckoos were brooded more on average than three or four Warblers of the same age, for a greater part of the nestling period and in longer spells. Thus the pattern of brooding by adult Warblers was not determined entirely endogenously but was modified by external stimuli.

Foods of insectivorous birds in forest of the Orongorongo Valley, Wellington, New Zealand

Abstract Foods are described from analysis of faeces and castings of adult riflemen (Acanthisitta chloris), hedge sparrows (Prunella modularis), whiteheads (Mohoua albicilla), grey warblers (Gerygone igata), fantails (Rhipidura fuliginosa), and pied tits (Petroica macrocephala toitoi), and of nestling riflemen and pied tits, inhabiting indigenous forest in the North Island of New Zealand. Beetles, spiders, and caterpillars were important to all 6 species. Differences in diet are shown to be related to the birds' feeding habits. Information is given on the seasonal distribution and abundance of some invertebrate foods. Seasonal changes in diet were small, probably reflecting the rather equable oceanic climate of New Zealand, where invertebrates are available throughout the year. Fruits and other vegetable matter were shown to occur to a varying extent in the diet of all 6 species.

BREEDING OF THE GREY WARBLER GERYGONE IGATA AT KAIKOURA, NEW ZEALAND

SummaryI studied the breeding of Grey Warblers Gerygone igata (Muscicapidae: Acanthizinae) in forest near Kaikoura, New Zealand, between 1976 and 1979. Only males sang and singing occurred all year. From late July to January pairs defended self‐contained territories of 0·25–1·73 ha but they occupied larger home ranges when not breeding. Territorial adults were strictly sedentary all year. The average annual mortality of breeding adults was 18·5% and the predicted life‐expectancy 4·9 years, which is remarkable in a bird weighing 6–7 g.The breeding season from first building to last fledging was six months long and it began early. Exceptionally, Grey Warblers may build and lay before the shortest day. As the season progressed warblers nested lower on average, both in absolute terms and relative to the tree nested in and canopy at the site. Warblers built in 7–27 days then delayed up to eight days before laying. Only females built and at no stage of breeding did males feed their mates. Both sexes fed the young.Grey Warblers laid for 15–16 weeks of the year and first clutches were laid asynchronously during 5–6 weeks. Eggs of a clutch appeared at two‐day intervals and each egg weighed 1·5 g when fresh (23% of mean adult weight). Clutch size was nearly constant (mean 3·9, mode 4, range 3–5). The incubation period was 17–21 days (mean 19·5 days) and the nestling period 15–19 days (mean 17·2 days). On average the clutch hatched over 1·4 days, even though incubation commenced with the laying of the last egg.Nestlings reached maximum weight on Days 13–14 on average and then receded in weight by 4%, apparently through loss of water. All healthy nestlings exceeded mean adult weight during development by up to 39%. Nestlings from broods of two were at first lighter on average than those from larger broods, but in the second half of the nestling period twins were significantly the heaviest.Grey Warblers were fed for 28–35 days after fledging and they survived well while dependent on parents. Fledglings dispersed up to 3 km or more at independence and only 5% per annum joined the breeding population.Of nests that received eggs, 42% produced at least one fledgling. On average each breeding adult raised 2·0 fledglings per season. Of 265 eggs in 73 nests 70% hatched and 38% produced fledglings. Of 185 nestlings 54% fledged. Probably the main cause of mortality of eggs and nestlings was predation by introduced rodents and mustelids.Grey Warblers raise two small broods slowly during a long breeding season, rather than investing in one large quickly‐reared brood. In New Zealand's mild climate the warbler's food supply may not decline severely in winter, and the population of warblers may remain so close to the limit set by food that extra for breeding is hard to obtain. Thus the breeding strategy may be adapted to a restricted food supply.

Abundance, feeding, and morphology of passerine birds at Kowhai Bush, Kaikoura, New Zealand

Abstract Five-minute stationary counts of birds at Kowhai Bush over 17 months suggest that the scores for grey warblers and chaffinches may reflect vocal conspicuousness, rather than abundance, and that the scores for shining cuckoos, goldfinches, and redpolls may reflect vocal and visual conspicuousness in combination. Counts in three types of kanuka forest show that cuckoos, robins, and bellbirds favoured the more dense and diverse suocessional stages; that riflemen, brown creepers, fantails, chaffinches, goldfinches, and redpolls were most abundant in less mature habitats; and that warblers and silvereyes were almost uniformly common. Cuckoos and robins overlapped the most in use of habitat, robins and redpolls the least. For both warblers and robins, indices of abundance varied between two of the habitats in proportion to the densities of resident adults, permitting calibration of the indices. Excepting creepers and robins, native species were apparently less abundant at Kowhai Bush than in climax for...

Black-Throated Gray Warbler - A Saskatchewan First

Black-Throated Gray Warbler - A Saskatchewan First

Black-Throated Gray Warbler at Miami, Florida

Black-Throated Gray Warbler at Miami, Florida

Black-Throated Gray Warbler on the Coast of South Carolina

Black-Throated Gray Warbler on the Coast of South Carolina

The Grey Warbler and New Zealand Cuckoos

The Grey Warbler and New Zealand Cuckoos

Black-Throated Gray Warbler in Massachusetts

Black-Throated Gray Warbler in Massachusetts

Two Oregon Warblers

D URING the warm days of May when the mystery of life seems suddenly unveiled in a miraculous manner, I often frequent a woody retreat above the old mill dam on Fulton creek. A clump of firs and maples overhang where the limpid water whirls gurgling among the gray rocks. Star flowers gleam from the darker places of shade, white anemones are scattered among grass blades and ferns, and Linna~an bells overhang the moss-covered logs. This is the haunt of the black-throated gray warbler. a Just below the brow of the hill half a mile above the creek, a little spring bubbles out of an alder copse. Instead of trickling down the hillside like an ordinary streamlet, the water scatters and seeps into the spongy soil. This forms a wet place an acre or so in extent over which has grown a rich growth of swamp grass. This is the yellow-throat'sb home. I call it the Witch's Garden. I have a great admiration for the little feathered individual dressed in gray because his extreme shyness is a good indication of his finer nature. But there is a fascination about lying in the shade of the tall fir and listening to the fanciful call of yellow-throat. You may hear him and his mate almost any time of the day calling Witch-et-y! Witch-et-y ! Yes, you may hear him but seldom see him.

Notes on the Black-Throated Gray Warbler

Notes on the Black-Throated Gray Warbler