Nosa
Bridled White-eye (Zosterops conspicillatus)
Order: Passeriformes
Family: Zosteropidae
CHamoru Names: Nosa
SPECIES OVERVIEW
Description: A sexually monomorphic forest bird with a white ring of feathers circling both eyes, a characteristic of many members of the avian Family Zosteropidae. The head, back, and wings of the Saipan subspecies (Z. c. saypani) are olive green and underparts are pale yellowish- white (Baker 1951). Legs and feet are olive-gray and the bill is blackish gray (Marshall 1949, Baker 1951).
Distribution and Status: The Saipan subspecies is endemic to the Mariana Islands and is common on Saipan, Tinian, and Aguiguan. The total populations on these three islands, respectively, were reported in 1982 to be approximately 229,000, 241,000 and 7,000 birds (Engbring et al. 1986). Later DFW and USFWS bird surveys of these islands yielded mean abundance estimates for the subspecies.
Camp et al. 2009), 225,360 on Tinian in 2008 (95% CI 193,080 – 283,200; Camp et al. 2012), and 50,205 on Aguiguan in 2008 (95% CI 37,902 – 68,235; Amidon et al. in review). The Guam subspecies (Z. c. conspicillatus) is now believed to be extinct (Wiles et al. 2003).
Habitat: Nosa is considered a habitat generalist. Although found primarily in forested areas (Stott 1947; Engbring et al. 1986; Craig 1989, 1996), they occur in a variety of cover types, including native limestone forest, introduced Leucaena leucocephala thickets, Casuarina forest, beach strand, swordgrass savannah, and suburban areas. Research on nesting densities in native limestone forest and L. leucocephala thickets indicate that the Saipan subspecies nests predominately in L. leucocephala thickets, however (Sachtleben 2005).
Food and Feed Habits: While the nosa appears to feed primarily on insects, they have been observed also foraging on the fruits of Momordica charantia, Passiflora foetaeda, Jasminum marianum, Premna obtusifolia, Ficus spp., Melanolepis multiglandulosa, Artocarpus spp., Pipturus argenteus, Lantana camara, Carica papaya, and Muntingia calabura (Engbring et al. 1986; Craig 1989, 1996). In 2007, consumption of the fruits of Coccinia grandis was evident in the droppings of all nosa captured on Saipan (H. Roberts, Mamphis Zoo, pers. comm.). They also have been observed probing flowers (presumably to feed on nectar) of Operculina vetricosa, Erythrina variegata, Pisonia grandis, Cynometra ramiflora, Premna obtusifolia, Psychotria mariana, Morinda citrifolia, Hibiscus tiliaceus, and Albizia lebbeck; eating the flowers of Mikania scandens, Jasminum marianum, Pisonia grandis, Cynometra ramiflora, and Leucaena leucocphala; and eating the seeds of Momordica charantia and Bidens pilosa (Engbring et al. 1986, Craig 1989, 1996).
Nosa have been observed foraging in 23 species of tree (Table 2) on Saipan, primarily by gleaning insects from leaves and branches in the outer canopy of limestone and Leucaena leucocephala forests (Craig 1989, 1996). However, they have also been observed hovering and sallying for insects and probing flowers (likely for nectar), bark, and dead and rolled leaves (Craig 1989). In addition, the subspecies has been observed foraging in the understory of forests, on the ground, and in Bidens pilosa and Miscanthus floridulus (Craig 1989, 1996).
Behavior: Nosa are reported to make several vocalizations. The most common is a call that Pratt et al. (1987) describe as a high-pitched tszeeip, often rapidly uttered and organized into a loose song. They have also been observed producing a scolding alarm call, often in response to the presence of Collared Kingfishers (Todiramphus chloris); Marshall 1946, Craig 1996).
Like many of the white-eyes in the family Zosteropidae, the Saipan subspecies is gregarious and often observed in flocks. These flocks typically consists of family groups of 3 to 5 individuals or larger flocks of 10 to 40 individuals, though larger flocks do often occur at flowering and fruiting trees (Craig 1989, 1996). No interspecific aggression has been noted to be initiated by nosa and the only such interaction described for the species (aside from scolding Collared Kingfishers) was of an individual foraging with a Nabaak (Craig 1996).
Breeding: Nosa likely breed year-round with distinct peaks during different portions of the year. Sachtleben (2005) reported nesting on Saipan from February to June with a distinct peak in February and March, while Pyle et al. (2012) reported birds on the island in breeding condition every month of the year. Craig (1996) reported breeding in January, February, August, and October and recorded food begging by juveniles year-round. On Tinian, Yamashina (1932) reported collecting three active nests in January.
Nesting: Nests are typically composed of fine roots and fibers, a small quantity of cotton wool, and feathers (Yamashina 1932). Sachtleben (pers. comm., 2005) recorded the dimensions of 87 Bridled White-eye nests on Saipan, reporting a mean nest height of 49 mm (range = 35-70 mm) a mean cup depth of 33 mm (range = 23-41 mm), a mean cup diameter of 40 mm (range = 32-48), and a mean outer nest diameter of 61 mm (range = 51-72 mm).
Nosa have been reported building nests on ten tree species, six vine species, and one herbaceous species (Table 2). In 2004, Sachtleben (pers. comm., 2005) documented the site characteristics of 115 nosa nests on Saipan, reporting a mean nest height of 2.3 m (range = 0.7 – 5.2 m), a mean nest tree height of 4.3 m (range = 1.2-10.8 m), and a mean distance of nests from the boles of nest trees of 42 cm (range = 0 - 263 cm). Sachtleben (pers. comm. 2005) reported that the mean number of branches used for nest support was 3 (range = 1- 7) and that the mean diameter of these branches was 2 mm (range = 1-6 mm).
Eggs, Incubation, Hatching, Growth, and Development: Clutch sizes range from 1 to 3 pale blue eggs (Yamashina 1932). Egg laying ranges from 2 to 3 days and incubation from 9 to 12 days (Sachtleben 2005), and fledging occurs 11 to 14 days post-hatching (Sachtleben 2005). The duration of post-fledging parental care is unknown. Sachtleben (pers. comm., 2005) described chick growth for the nosa as follows:
Day 0:
approximately 1.5 cm (1 – 2cm) in length, naked, with light-medium pink skin and two “tufts” of downy feathers on their head (appearance-wise, a cross between horns and eyebrows).
Approximately 2 cm long, and naked with medium-dark pink skin. Otherwise, little change from Day 0.
Day 1: Day 3:
2.5 cm (2 – 3cm) long, medium-dark pink skin, wing pins 2 – 5 mm in length, head and back pins visible under skin but not erupted or barely so, two tufts on the head either remaining or no longer present.
Approximately 3.5 cm long, medium-light pink skin, back pins 1 – 2 mm in length, and wing pins ≥3 mm long.
Day 4: Day 6:
3.5 cm (3 – 4 cm) long, wing pins 6 – 7 mm in length, feathers possibly erupted from wing pins greenish and approximately 1 – 2 mm in length. Back pins 2 – 4 mm in length, feathers possibly erupted from back pins greenish and approximately 1 – 2 mm in length, head pins 3 - 4 mm long, white belly feathers in 2 lines, exposed skin light or medium pink, and eyes still closed or cracking open.
Day 8: Day 9:
4.5 cm long, fully feathered, olive grey-green, and eyes opened. Approximately 4 – 4.5 cm long, mostly feathered, olive grey-green, eyes opened, and wing feathers dark grey.
Day 10:
Approximately 5 – 5.5 cm long, fully feathered, wings dark grey and back grey-green.
Day 12:
Approximately 5 – 5.5 cm long, greenish and fully feathered, belly appearing downy, and often perching on rim of the nest. Chicks will force-fledge at this age and fly well.
Threats: The Bridled White-eye is abundant and widespread on the islands of Saipan, Tinian, and Aguiguan, and is not currently considered threatened or endangered by the Federal or Commonwealth governments. The primary threats to the species are newly introduced predators and possible diseases, such as the Brown Treesnake and West Nile Virus, respectively.
Bridled White-eye (Zosterops conspicillatus)
Order: Passeriformes
Family: Zosteropidae
CHamoru Names: Nosa
SPECIES OVERVIEW
Description: A sexually monomorphic forest bird with a white ring of feathers circling both eyes, a characteristic of many members of the avian Family Zosteropidae. The head, back, and wings of the Saipan subspecies (Z. c. saypani) are olive green and underparts are pale yellowish- white (Baker 1951). Legs and feet are olive-gray and the bill is blackish gray (Marshall 1949, Baker 1951).
Distribution and Status: The Saipan subspecies is endemic to the Mariana Islands and is common on Saipan, Tinian, and Aguiguan. The total populations on these three islands, respectively, were reported in 1982 to be approximately 229,000, 241,000 and 7,000 birds (Engbring et al. 1986). Later DFW and USFWS bird surveys of these islands yielded mean abundance estimates for the subspecies.
Camp et al. 2009), 225,360 on Tinian in 2008 (95% CI 193,080 – 283,200; Camp et al. 2012), and 50,205 on Aguiguan in 2008 (95% CI 37,902 – 68,235; Amidon et al. in review). The Guam subspecies (Z. c. conspicillatus) is now believed to be extinct (Wiles et al. 2003).
Habitat: Nosa is considered a habitat generalist. Although found primarily in forested areas (Stott 1947; Engbring et al. 1986; Craig 1989, 1996), they occur in a variety of cover types, including native limestone forest, introduced Leucaena leucocephala thickets, Casuarina forest, beach strand, swordgrass savannah, and suburban areas. Research on nesting densities in native limestone forest and L. leucocephala thickets indicate that the Saipan subspecies nests predominately in L. leucocephala thickets, however (Sachtleben 2005).
Food and Feed Habits: While the nosa appears to feed primarily on insects, they have been observed also foraging on the fruits of Momordica charantia, Passiflora foetaeda, Jasminum marianum, Premna obtusifolia, Ficus spp., Melanolepis multiglandulosa, Artocarpus spp., Pipturus argenteus, Lantana camara, Carica papaya, and Muntingia calabura (Engbring et al. 1986; Craig 1989, 1996). In 2007, consumption of the fruits of Coccinia grandis was evident in the droppings of all nosa captured on Saipan (H. Roberts, Mamphis Zoo, pers. comm.). They also have been observed probing flowers (presumably to feed on nectar) of Operculina vetricosa, Erythrina variegata, Pisonia grandis, Cynometra ramiflora, Premna obtusifolia, Psychotria mariana, Morinda citrifolia, Hibiscus tiliaceus, and Albizia lebbeck; eating the flowers of Mikania scandens, Jasminum marianum, Pisonia grandis, Cynometra ramiflora, and Leucaena leucocphala; and eating the seeds of Momordica charantia and Bidens pilosa (Engbring et al. 1986, Craig 1989, 1996).
Nosa have been observed foraging in 23 species of tree (Table 2) on Saipan, primarily by gleaning insects from leaves and branches in the outer canopy of limestone and Leucaena leucocephala forests (Craig 1989, 1996). However, they have also been observed hovering and sallying for insects and probing flowers (likely for nectar), bark, and dead and rolled leaves (Craig 1989). In addition, the subspecies has been observed foraging in the understory of forests, on the ground, and in Bidens pilosa and Miscanthus floridulus (Craig 1989, 1996).
Behavior: Nosa are reported to make several vocalizations. The most common is a call that Pratt et al. (1987) describe as a high-pitched tszeeip, often rapidly uttered and organized into a loose song. They have also been observed producing a scolding alarm call, often in response to the presence of Collared Kingfishers (Todiramphus chloris); Marshall 1946, Craig 1996).
Like many of the white-eyes in the family Zosteropidae, the Saipan subspecies is gregarious and often observed in flocks. These flocks typically consists of family groups of 3 to 5 individuals or larger flocks of 10 to 40 individuals, though larger flocks do often occur at flowering and fruiting trees (Craig 1989, 1996). No interspecific aggression has been noted to be initiated by nosa and the only such interaction described for the species (aside from scolding Collared Kingfishers) was of an individual foraging with a Nabaak (Craig 1996).
Breeding: Nosa likely breed year-round with distinct peaks during different portions of the year. Sachtleben (2005) reported nesting on Saipan from February to June with a distinct peak in February and March, while Pyle et al. (2012) reported birds on the island in breeding condition every month of the year. Craig (1996) reported breeding in January, February, August, and October and recorded food begging by juveniles year-round. On Tinian, Yamashina (1932) reported collecting three active nests in January.
Nesting: Nests are typically composed of fine roots and fibers, a small quantity of cotton wool, and feathers (Yamashina 1932). Sachtleben (pers. comm., 2005) recorded the dimensions of 87 Bridled White-eye nests on Saipan, reporting a mean nest height of 49 mm (range = 35-70 mm) a mean cup depth of 33 mm (range = 23-41 mm), a mean cup diameter of 40 mm (range = 32-48), and a mean outer nest diameter of 61 mm (range = 51-72 mm).
Nosa have been reported building nests on ten tree species, six vine species, and one herbaceous species (Table 2). In 2004, Sachtleben (pers. comm., 2005) documented the site characteristics of 115 nosa nests on Saipan, reporting a mean nest height of 2.3 m (range = 0.7 – 5.2 m), a mean nest tree height of 4.3 m (range = 1.2-10.8 m), and a mean distance of nests from the boles of nest trees of 42 cm (range = 0 - 263 cm). Sachtleben (pers. comm. 2005) reported that the mean number of branches used for nest support was 3 (range = 1- 7) and that the mean diameter of these branches was 2 mm (range = 1-6 mm).
Eggs, Incubation, Hatching, Growth, and Development: Clutch sizes range from 1 to 3 pale blue eggs (Yamashina 1932). Egg laying ranges from 2 to 3 days and incubation from 9 to 12 days (Sachtleben 2005), and fledging occurs 11 to 14 days post-hatching (Sachtleben 2005). The duration of post-fledging parental care is unknown. Sachtleben (pers. comm., 2005) described chick growth for the nosa as follows:
Day 0:
approximately 1.5 cm (1 – 2cm) in length, naked, with light-medium pink skin and two “tufts” of downy feathers on their head (appearance-wise, a cross between horns and eyebrows).
Approximately 2 cm long, and naked with medium-dark pink skin. Otherwise, little change from Day 0.
Day 1: Day 3:
2.5 cm (2 – 3cm) long, medium-dark pink skin, wing pins 2 – 5 mm in length, head and back pins visible under skin but not erupted or barely so, two tufts on the head either remaining or no longer present.
Approximately 3.5 cm long, medium-light pink skin, back pins 1 – 2 mm in length, and wing pins ≥3 mm long.
Day 4: Day 6:
3.5 cm (3 – 4 cm) long, wing pins 6 – 7 mm in length, feathers possibly erupted from wing pins greenish and approximately 1 – 2 mm in length. Back pins 2 – 4 mm in length, feathers possibly erupted from back pins greenish and approximately 1 – 2 mm in length, head pins 3 - 4 mm long, white belly feathers in 2 lines, exposed skin light or medium pink, and eyes still closed or cracking open.
Day 8: Day 9:
4.5 cm long, fully feathered, olive grey-green, and eyes opened. Approximately 4 – 4.5 cm long, mostly feathered, olive grey-green, eyes opened, and wing feathers dark grey.
Day 10:
Approximately 5 – 5.5 cm long, fully feathered, wings dark grey and back grey-green.
Day 12:
Approximately 5 – 5.5 cm long, greenish and fully feathered, belly appearing downy, and often perching on rim of the nest. Chicks will force-fledge at this age and fly well.
Threats: The Bridled White-eye is abundant and widespread on the islands of Saipan, Tinian, and Aguiguan, and is not currently considered threatened or endangered by the Federal or Commonwealth governments. The primary threats to the species are newly introduced predators and possible diseases, such as the Brown Treesnake and West Nile Virus, respectively.
Nosa - Kasey Clarke