Notes on the Behavior of the Melodious Blackbird (Dwes Dives)
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Condor 85:453-460 :L‘ The Cooper Ornithological Soaety 1983 NOTES ON THE BEHAVIOR OF THE MELODIOUS BLACKBIRD (DWES DIVES) GORDON H. ORIANS ABSTRACT.-Both sexes of the Melodious Blackbird (Dives dives) defend ter- ritories by vigorous duetting, bill-up displays,and supplantingattacks. These birds forage primarily on the ground in open areas and also forage throughout canopies of tall trees, especially pines. Most food is obtained by gaping;much fruit is taken when available. Displays of this speciesresemble those of other icterids. Vocal- izations are loud and clear and include many whistles. Most of the sounds are made by individuals of both sexes,but some are restricted to one sex. The Scrub Blackbird (D. warszewiczz’)resembles the Melodious Blackbird in many respects, but several pairs occupy common foraging grounds and are tolerated near one another’s nests. The Melodious Blackbird (Dives dives) occu- dition, I spent one day watching D. warszew- pies a relatively restricted rangeon the Atlantic iczi in the Andes of central Peru, 80 km ENE slope of Central America from Vera Cruz, of Lima, near Matucana, Departamento de Mexico, to northern Nicaragua. It inhabits pri- Lima (1 lo5 1’S, 76”23’W, elev. ca. 2,600 m). marily lowlands but occurs in pine forests to Sonograms were made from recordings pro- an elevation of nearly 2,000 m in Guatemala vided by the Library of Natural Sounds, Cor- (Skutch 1954). The closely related Scrub nell Laboratory of Ornithology. Blackbird (D. warszewiczz),sometimes consid- My most extensive observations, and the ered a race of D. dives (Paynter 1968) occurs only ones on breeding birds, were carried out in arid country in southwestern Ecuador and in an open woodland of Caribbean Pine (Pinus western Peru. Knowledge of the Central Amer- caribaea) in the Mountain Pine Ridge, Belize. ican form is limited to that gatheredby Skutch The territory of the pair I watched most of the (1954). Only distributional information has time included the grounds of Blancaneaux been published for the South American form. Lodge, surrounding pine woodland, an air- Most investigations of icterids have been strip, and a sectionof pine woodsheavily grazed carried out on temperate-zone species, espe- by cattle. Ground cover was composed pri- cially those with polygynous mating systems. marily of several species of tough wiregrass Very little is known of mating systems and (Panicurn spp. and Paspalum spp. especially roles of the sexesamong tropical species,many Paspalum pectinatum). The sparseshrub cov- of which are probably monogamous. The mo- er was dominated by Clidemia rubra, Miconia nogamousMelodious Blackbird breeds in ear- albicans (Melastomaceae), and Byrsonima ly successionalhabitats where changesin vege- crussifolia(Malpighiaceae). In shadier areas of tation are rapid. Therefore, individuals may dense pine woods there was a sparse ground often have to shift their breeding sites from cover of Coccosypselumsp. (Rubiaceae) and year to year. Under these circumstances, re- Ageratum sp. (Compositae). Mistletoes (Ar- lationships between members of a pair and ceuthobium vaginatum and Psittacanthus ca- interactions among pairs may be particularly lyculatus)were common on pine bolesand were interesting and complex, even though popu- in flower in April. lations of this speciesare believed to be resi- The Honduras study site, one km W of Sig- dent throughout their range. In this paper I uatepeque (elev. 1,080 m), consisted of a report my observationson the behavior, social mixed-age stand of Pinus oocarpaabout 25 m organization and ecology of this little-known tall, adjacent to open pastures.Under gaps in bird gathered during two visits to Central the canopy there was a rich shrub flora dom- America. inated by Calliandra houstoniana (Legumi- nosae). Little grassand few herbs were in the METHODS forest even though it had not been grazed for I watched D. dives in eastern Guatemala, many years. 17-18 November 1971 and 16-17 June 1972; I observed Scrub Blackbirds on 6 May 1974 southeasternMexico 2-10 April 1972; Blan- on a terraced, agricultural hillside in otherwise caneaux Lodge, Mountain Pine Ridge, Belize, rugged,arid mountain terrain. Most of the tall 14-30 April and 1-15 June 1972; and Sig- trees in the area were Eucalyptus, but there uatepeque,Honduras, 17-30 May 1972. In ad- were also a few Araucaria, Schinus,Ficus, Pru- [4531 454 GORDON H. ORIANS y1us,and others I was unable to identify. The and exited over the opposite edge. The four non-agricultural areas were covered with low eggswere bright, robin’s-egg blue with a few shrubby vegetation interspersedwith large co- dark brown blotches at the larger end. One of lumnar cacti. The steeper slopes were largely the eggs,which failed to hatch, measured 26 x bare ground but with frequent patches of ter- 18 mm and had six medium-sized dark blotch- restrial bromeliads. Flowering was prevalent es and about 10 very small ones. at the time and the blackbirds were breeding. The establishedterritorial pair received con- siderable pressure from roving individuals. RESULTS During three mornings in April (7 h of obser- vation), I saw a vigorous territorial encounter NESTING with a second pair that lasted 23 min. During In easternGuatemala in November 197 1 I saw the incubation period, I saw three encounters Melodious Blackbirds singly or in pairs along 7, 3, and 9 min long, with other pairs during roads, in gardens, and in recently abandoned a 4.5-h morning watch. When young were in fields and brushy pastures.I heard a great deal the nest, I watched four mornings for a total of singing,but I saw no evidence of breeding. of 12.25 h, during which time I saw six en- In April 1972 these birds were common from counters which lasted 2, 3, 4, 4, 4, and 6 min. just south of Tampico through the drier parts Two of theseencounters were with singlebirds; of the Yucatan Peninsula. All were in pairs the others were with pairs. Since I watched except for those in a large flock foraging in a almost exclusively at the nest itself during in- dry, stubby forest in La Venta Park, Villa Her- cubation and nestling stages,I could not see mosa. Although the birds at La Venta foraged encountersnear the boundary of the territory. in groups, they sang constantly for the 2 h I During the 4.5 h I watched the nest when it observed them, and birds appeared to be as- had eggs, only the female incubated. Unlike sociating in pairs within the flock. At Blan- Skutch (1954), I did not see the male feed the caneaux Lodge and in eastern Guatemala in incubating female. Both sexes fed the young, June I never saw groups larger than two. At but the female wasthe chief provider, as Skutch Siguatepequeon 23 May, where I found up to found in Guatemala. During 12.25 h of watch- four pairs foraging together on the ground un- ing at the nest with nestlings,I saw the female der pines, the pair units were obvious. Al- bring food 32 times, the male only 3 times. though limited, theseobservations suggest that These data are biased, however, because the Melodious Blackbirds may remain perma- male was much more sensitive to my presence nently paired even in areas where they form than the female, and when she came in with flocks during the non-breeding season. food, he often flew toward me and beganstrong At BlancaneauxLodge theseblackbirds were scoldingeven though he had not been reacting highly territorial, taking up defenselong before to me in her absence.He seemed to dissuade nesting began in spring. The pair at the Lodge the female from going to the nest on three duetted loudly and conspicuouslyin mid-April, occasions,and five times when he approached a month before they built their nest, and they with food he failed to go to the nest. spent much time traveling around the periph- The male never brooded the young after ery of their territory. Both members of the pair feeding them, but the female did so on 37.5% sporadically picked up nesting material in late of her visits, brooding them 20.3% of the total April but did not build a nest. They often vis- time I watched the nest. Brooding continued ited clumps of dead pine needles in two dif- until the young were six to seven days old, the ferent trees, but neither tree was subsequently last day of observation before the nest was used for the nest. I was absent during the nest- depredated. During the incubation and nest- building period, but the young hatched 2-3 ling periods, the male spent most of his time June, indicating that egg laying began about guarding.Even when the female flew some dis- 17-l 8 May. According to Skutch (1954) both tance to forage, the male usually remained sexesbuild. within sight of the nest. When he did leave, it The singlenest I found was about 7 m above was only briefly. During the incubation period, ground close to the trunk of a Pinus caribaea. he was out of sight of the nest only 47 min out It was slung from two very small adventitious of 4.5 h (17.4%). His periods of absence av- needle clumps and rested on a third. The nest eraged 9.4 min (range 2-27 min). During the was built almost entirely of dead pine needles, nestling period, he was absent for a total of with a modest lining of finer grasses,and ap- 145 min, out of 12.25 hours (19.7%) and he peared flimsy. The open nest-cup sloped to- was never gone longer than 16 consecutive ward the trunk, and the eggswere rolled to one minutes.