Ecology of breeding white-winged doves in the San Antonio metropolitan area
West, Leann Marie
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More than half of the total Texas breeding population of whitewinged doves (Zenaida asiatica) is now breeding outside the Lower Rio Grande Valley of Texas, and more than 50% of these birds can be found within the San Antonio area. Records indicate this population is increasing, suggesting that white-winged doves are finding suitable nesting habitat in urban areas. To obtain information on management needs for whitewings in urban areas, a study of the breeding ecology of the San Antonio population of white-winged doves was undertaken in 1991-1992. To determine dove distribution and abundance, 22 call count survey lines were placed in 5 habitat types. In addition, point surveys were conducted in 14 individual parks. Habitat types were: Residential areas <50 years of age, Residential areas >50 years of age, Parks <50 ha, Parks >50 ha, and the Downtown area. Peak levels of calling occurred in the third week in May in both years. Breeding pair density indices revealed Residential areas <50 years of age (16.405 nests/ha) and Residential areas >50 years of age (14.946 nests/ha) had greater breeding pair densities than other habitats (P < 0.001). Comparison of calling levels heard with numbers of nests found in the same area revealed that numbers of birds heard calling is related to number of nests found (R2 = 0.73, f < 0.001). However, when (n = 2) observations containing estimates >15 nests/point were removed from the model, no relationship was found <B2 = 0.002, f = 0.74). Call count surveys may not be an appropriate method of breeding population survey except in areas where whitewing density is high. Thirty-nine nest plots were used on the study area in 1991, and 44 in 1992. A total of 182 nests was found in 1991 and 215 in 1992. Residential areas <50 years of age had a higher nest density (42.9 nests/ha) than other habitats (f = 0.03). Nest success was lower in Residential areas <50 years of age over most other habitats in 1991 (P < 0.05). Little variation occurred in success rates among habitats in 1992. Young produced per pair of whitewings (i.e., production index) was lower in 1992 (1.378) than in 1991 (1.632) (f = 0.04). Use of Residential areas <50 years of age was greater than expected (f < 0.05), while use of other habitats was less than expected. Live oak and Arizona ash were preferred nest trees (f < 0.05), while other tree species were avoided. Residential areas <50 years of age was preferred whitewing habitat and high densities of live oak and Arizona ash within these areas suggested these tree species may be attracting doves to this habitat. White-winged dove feeding flights to fields were monitored hourly (0700-1900) from 14 June-15 August in 1992. No differences were found in numbers of doves departing for feeding fields among survey hours (f > 0.05). Numbers of doves making flights from feeding fields was lower during 0700, and 1300 hours than those occurring during 1700 hours (f < 0.05). Surveys of flights of whitewings leaving feeding fields to assess dove numbers should be attempted primarily around 1700 hours to obtain accurate estimates of the population. Two hundred and six adult males, 181 adult females, and 63 juvenile white-winged doves were collected in 1991-1992. Juveniles consumed more species of crop seeds (all common components of bird seed) than non-cultivated seeds (P = 0.008). Juveniles consumed greater levels of domestic sunflower (£ = 0.006) than adults. Juveniles may rely on bird feeders as their main food source and may not participate in feeding flights. Male whitewings consumed a greater diversity of crop seeds than females (E = 0.016). Females consumed more species of non-cultivated seeds than males (P = 0.039). Males and females consumed more crop species than non-cultivated species in May (£ = 0.001 and£ =0.002, respectively). Males also consumed more crop species than noncultivated species in June (£ = 0.01). Male and female diets had more non-cultivated species than crop species in July (£ = 0.006 and £ = 0.001, respectively) and August (£ = 0.003 and£= 0.001, respectively). Males and females consumed more native sunflower in July and August than in May (£ < 0.05). Females also consumed more native sunflower in July than in June (£ < 0.05). Tropic croton was consumed by male whitewings in greater amounts in July than in May (E < 0.05), and by females in greater amounts in August than in May (P < 0.05). Females also consumed more tropic croton than males (E = 0.038). Male whitewings are relying on crop seeds and possibly bird feeders for food to a greater overall extent than females, while both sexes may be relying on bird feeders in May. In contrast, females may be making more feeding flights during the breeding season than males, while both sexes may be depending on fields outside the city for food in July and August. A public relations program in the city to promote backyard bird feeding, plus purchase or leasing of agricultural fields outside the city to be managed for whitewing use may be appropriate techniques to manage white-winged doves in San Antonio.