Philip C. Stouffer

Use of Amazonian Forest Fragments by Understory Insectivorous Birds

We sampled understory insectivorous birds in Amazonian forest fragments from before isolation through 9 yr after isolation. We accumulated 3658 mist net captures of 84 insectivorous species in five 1-ha fragments and four 10-ha fragments. Abundance and species richness declined dramatically after isolation, even though fragments were separated from continuous forest by only 70-650 m. Three species of obligate army ant followers disappeared within the first 2 yr after isolation. Mixed-species flocks containing 13 commonly netted species disintegrated within 2-3 yr after isolation, although three species that dropped out of flocks persisted in fragments. Among insectivores not associated with flocks or army ants, only two species of edge specialists were unaffected by frag- mentation. Overall, loss of forest insectivores was not compensated for by an increase in nonforest or previously uncommon species. Secondary vegetation surrounding fragments strongly affected use of fragments after isolation. Fragments surrounded by Vismia, the dominant regrowth where felled forest was burned and temporarily used as cattle pasture, remained depauperate. In contrast, many species returned to fragments by moving through regenerating forest dominated by Cec- ropia, which occurred in areas where the felled forest was not burned. Both 1- and 10-ha fragments surrounded by Cecropia were used by ant followers by 5 yr after isolation. Mixed-species flocks reassembled in 10-ha fragments surrounded by Cecropia by 7-9 yr after isolation, and augmented their group territories by foraging in secondary forest outside fragments. Solitary species were more variable in their responses, although several species returned to 10-ha fragments surrounded by Cecropia. Terrestrial insectivores, such as Scle- rurus leafscrapers and various antbirds, did not return to any fragments, and appear to be the group most vulnerable to fragmentation. Ordination of the insectivore community showed that 1-ha fragments diverged from their pre-isolation communities more than did 10-ha fragments. Communities in 10-ha fragments surrounded by Cecropia were more closely associated with pre-isolation com- munities than those in fragments surrounded by Vismia. Over time, communities in 10-ha fragments surrounded by Cecropia became more like pre-isolation communities, although communities in other fragments generally continued to diverge.

Rates of species loss from Amazonian forest fragments

In the face of worldwide habitat fragmentation, managers need to devise a time frame for action. We ask how fast do understory bird species disappear from experimentally isolated plots in the Biological Dynamics of Forest Fragments Project, central Amazon, Brazil. Our data consist of mist-net records obtained over a period of 13 years in 11 sites of 1, 10, and 100 hectares. The numbers of captures per species per unit time, analyzed under different simplifying assumptions, reveal a set of species-loss curves. From those declining numbers, we derive a scaling rule for the time it takes to lose half the species in a fragment as a function of its area. A 10-fold decrease in the rate of species loss requires a 1,000-fold increase in area. Fragments of 100 hectares lose one half of their species in <15 years, too short a time for implementing conservation measures.

BIRD COMMUNITIES IN TWO TYPES OF ANTHROPOGENIC SUCCESSIONAL VEGETATION IN CENTRAL AMAZONIA

When primary forest in central Amazonia is cut and abandoned, the plant succession is dominated by Cecropia spp., whereas when it is cut and burned for pastures, the regrowth vegetation is dominated by Vismia spp. The bird communities of these two regrowth forest types were sampled at six sites (9-13 years old) using mist-nets and obser- vations. Bird species richness was similar between the two forest types. Cecropia regrowth, however, was richer for strictly forest bird species than was Vismia regrowth. Mixed-flock species and ant-following birds were significantly more abundant in the Cecropiu second growth, whereas nonforest insectivores and omnivores were more common in Vismia re- growth. The type of regrowth was found to influence bird species composition in the study sites. These results suggest that the type of human disturbance has an important role in determining the bird communities that occupy early successional areas in central Amazonia.

Egg removal and intraspecific brood parasitism in the European starling (Sturnus vulgaris).

SummaryFrom 1983 to 1986 we monitored 284 European starling (Sturnus vulgaris) nests in New Jersey for evidence of intraspecific brood parasitism and egg removal during the laying period. Egg removal occurred significantly more often at nests where intraspecific brood parasitism was detected (12 of 35 nests, 34%) than at unparasitized nests (23 of 249 nests, 9%). Brood parasitism (92% of parasitized nests) and egg removal (74% of nests with egg removal) were most common at nests where egg laying began in April of each year (i.e., early nests). Egg removal occurred at 26 (19%) and brood parasitism at 32 (23%) of 138 early nests. Both brood parasitism and egg removal were concentrated during the first four days in the laying period when brood parasitism is most likely to be successful and when host nests are most vulnerable to parasitism (Romagnano 1987). Both parasitism and removal usually involved a single egg at each nest. We detected brood parasitism and egg removal on the same day at five of 12 nests (42%) where both were observed. Because starlings do not remove foreign eggs from their nests once they begin laying (Stouffer et al. 1987) we hypothesize that parasite females sometimes removed host eggs while parasitizing nests.

Understory Bird Communities in Amazonian Rainforest Fragments: Species Turnover through 25 Years Post-Isolation in Recovering Landscapes

Inferences about species loss following habitat conversion are typically drawn from short-term surveys, which cannot reconstruct long-term temporal dynamics of extinction and colonization. A long-term view can be critical, however, to determine the stability of communities within fragments. Likewise, landscape dynamics must be considered, as second growth structure and overall forest cover contribute to processes in fragments. Here we examine bird communities in 11 Amazonian rainforest fragments of 1–100 ha, beginning before the fragments were isolated in the 1980s, and continuing through 2007. Using a method that accounts for imperfect detection, we estimated extinction and colonization based on standardized mist-net surveys within discreet time intervals (1–2 preisolation samples and 4–5 post-isolation samples). Between preisolation and 2007, all fragments lost species in an area-dependent fashion, with loss of as few as <10% of preisolation species from 100-ha fragments, but up to 70% in 1-ha fragments. Analysis of individual time intervals revealed that the 2007 result was not due to gradual species loss beginning at isolation; both extinction and colonization occurred in every time interval. In the last two samples, 2000 and 2007, extinction and colonization were approximately balanced. Further, 97 of 101 species netted before isolation were detected in at least one fragment in 2007. Although a small subset of species is extremely vulnerable to fragmentation, and predictably goes extinct in fragments, developing second growth in the matrix around fragments encourages recolonization in our landscapes. Species richness in these fragments now reflects local turnover, not long-term attrition of species. We expect that similar processes could be operating in other fragmented systems that show unexpectedly low extinction.

DENSITY, TERRITORY SIZE, AND LONG-TERM SPATIAL DYNAMICS OF A GUILD OF TERRESTRIAL INSECTIVOROUS BIRDS NEAR MANAUS, BRAZIL

Abstract From 1994 to 2003, I annually surveyed terrestrial insectivorous birds in a 100-ha plot within continuous rainforest near Manaus, Brazil. I used spot-map registrations and radiotagged birds to estimate territory size and density on the plot for 13 species. As in the few previous studies of Amazonian birds, territory sizes were large (mean = 13.0 ha) and densities were low (mean = 3.4 pairs per 100 ha). The most common species, Formicarius colma, was the only species with >10 pairs per 100 ha, and one of four species (with Myrmeciza ferruginea, Conopophaga aurita, and Corythopis torquatus) to have territories of <7.0 ha. On average, each species occupied 34% of the plot, with only four species (F. colma, Grallaria varia, F. analis, and M. ferruginea) ever occupying >50% in any year. Territories appeared and disappeared between surveys; ∼71% of territories detected in a given survey were present in the next survey. The two rarest species, Myrmothera campanisona and Hylopezus macularius, were absent from the plot in some years. Across species, territory stability was positively correlated with abundance; more common species had more stable density among years than rare species. Although past research has shown territory stability for the most common species of Neotropical rainforest birds, my results suggest that rarer species, which constitute the bulk of the avifauna, may show greater fluctuation in abundance. I compared my results to similar data from lowland rainforests in Panama, French Guiana, Ecuador, and Peru. Species richness was lowest in Panama, but comparable among the Amazonian sites. Panama also had the highest biomass and smallest territory sizes. Interestingly, relative abundances of species shared among sites were not necessarily similar. With the exception of Conopophaga spp., all species or replacement species shared among sites were at least twice as abundant at one site as at another. Relative abundance within genera also differed among sites for Sclerurus and Formicarius. The sparse data available so far suggest that individual species show considerable spatial variation in abundance across Amazonia, though the mechanisms and the texture of the patterns remain unknown. Densidade, Tamanho do Território, e Dinamismo Espacial ao Longo Prazo das Aves Insetívoras Terrestres perto de Manaus, Brasil

Roosting behavior and group territoriality in American crows

-Cooperative groups of American Crows (Corvus brachyrhynchos) maintain group territories year-round while often traveling long distances to roost communally at night. Our goal was to discover how territorial crows resolve the conflict between the cohesive nature of group behavior with requirements of dispersal to roost communally. We color-marked crows to study group composition over two years, and radio-tagged crows to study movement among roosts, territories, and feeding areas. Most crows showed diurnal fidelity to the group territory throughout the year. Yet, most birds frequently left territories during the day to forage up to 4 km away. At night, crows roosted either on their territory or 18 km away at a large roost adjacent to a landfill. Crows roosted on territories more often in spring (87%) than in winter (42%). Group cohesion was high on territories, yet we found no evidence for group behavior away from territories. Crows arrived singly both to territories in the morning and to the communal roost in the afternoon. Group cohesion for territorial crows appears to be based on decisions of individuals to return to territories from distant roosting and foraging sites. Group cohesion on territories is tied to retention of breeding sites, whereas dispersal for communal roosting likely is linked to benefits derived from foraging away from territories, particularly in winter when physiological stress is greatest and territorial food supplies are lowest. Received 10 May 1996, accepted 9 April 1997. COOPERATIVE BREEDING AND COMMUNAL ROOSTING in large aggregations have attracted considerable recent attention (e.g. Allen and Young 1982, Brown 1987, Caccamise 1993). Cooperative breeding and communal roosting are forms of group behavior, yet we know of no studies that have simultaneously examined relationships between these behaviors. Occurrence of both behaviors in a single species apparently is uncommon and may explain the lack of attention from researchers. American Crows (Corvus brachyrhynchos) offer the opportunity to examine relationships between cooperative breeding (Chamberlain-Auger et al. 1990) and communal roosting (Stouffer and Caccamise 1991a) because crows frequently travel to large communal roosts, yet they live in stable groups that breed cooperatively and defend year-round territories. In the northeastern United States, large com1 E-mail: caccamis@rci.rutgers.edu 2 Present address: Department of Vertebrate Ecology, Institute of Ecology, Polish Academy of Science, 05-092 Lomianki, n. Warsaw, Dziekanow Lesny, Poland. 3Present address: Department of Biological Sciences, Southeastern Louisiana University, Hammond, Louisiana 70402, USA. munal roosts of American Crows form each evening from late summer through early spring. The largest aggregations develop in winter (Goodwin 1976). Cooperative breeding and communal roosting have what appear to be conflicting requirements in that group territorial behavior requires group cohesion on territories, whereas communal roosting requires travel to distant sites with long absences from territories. It is not known how stable groups occupying territories during the day are related to large assemblages that form communal roosts at night. Nor is it known why individual crows that belong to stable groups abandon territories to join distant aggregations at communal roosts. Our goal was to understand how crows resolve apparent conflicts between the group cohesion required for cooperative breeding and territory defense with the temporary abandonment of territories necessary to join communal roosts. We used color-marking to study group composition and radiotelemetry to study movements of individuals among roosts, territories, and feeding areas.

Demographic effects of habitat selection by hermit thrushes wintering in a pine plantation landscape

Many species of migratory songbirds use silvicultural landscapes during the nonbreeding season. However, variation in habitat quality (i.e., the differential relative fitness value of habitats) resulting from different silvicultural management strategies and different age classes of these habitats is poorly understood. We studied the patterns of winter habitat selection by hermit thrushes (Catharus guttatus) among pine and hardwood habitats within a pine plantation landscape in southeastern Louisiana. We compared arrival patterns, relative abundance, territory size, body condition (mass, fat, and feather regrowth), between-winter site fidelity, and overwinter survivorship among birds in 3 age classes of even-aged loblolly pine (Pinus taeda) plantation and hardwood forest. We considered these demographic and condition measures as proximate estimates of relative fitness, and thus as indicators of habitat quality. Hermit thrushes in pole-stage (13-16 yr old) pine habitat had smaller territories, higher relative abundance, stayed leaner, and regrew feathers faster than birds in the other habitats, which suggests that this is the best habitat for wintering hermit thrushes among those we studied. Among other habitats, hardwood forest appears to be the lowest quality, but some measures (fat, territory size, and overwinter survivorship) indicate that the sapling-stage pine habitat is the lowest quality. Early arriving birds, disproportionately adults, avoid hardwoods, but beyond this we could find no evidence of segregation by age, sex, or body size among habitats. Our findings suggest that relatively small differences in habitat type and within-season changes in habitat quality can have important effects on the overwinter success of hermit thrushes. Pine plantations that differ in age by less than 10 years differentially affect the condition and demographics of wintering hermit thrushes. For conservation strategies to be successful, the dynamic spatial and temporal variation in habitat quality must be incorporated into models of population processes. Although pine plantation managers should consider multiple wildlife species, they also must be aware that individual species may have differential success among suitable habitats.

HOME-RANGE SIZE, RESPONSE TO FIRE, AND HABITAT PREFERENCES OF WINTERING HENSLOW'S SPARROWS

Abstract Henslows Sparrow (Ammodramus henslowii) is a declining, disturbance-dependent grassland bird that winters in the longleaf pine (Pinus palustris) ecosystem of the southeastern United States. During two winters (2001, 2002), we estimated the relative abundances, movement patterns, and habitat associations of Henslows Sparrows wintering in habitat patches differing in time since last burn (burn treatment). We conducted our study in southeastern Louisiana in Andropogon spp.-dominated longleaf pine savanna habitat. Henslows Sparrows were most abundant in savannas burned the previous growing season, with a mean relative abundance of 2.6 individuals/ha. The most dramatic decline occurred between burn year 0 and year 1 (first and second winters after burning), when mean relative abundance dropped to 1.0 individual/ha. Home-range size of radio-tagged birds was not correlated with burn treatment. All radio-tagged individuals maintained stable home ranges, with a mean size of 0.30 ha. Vegetation characteristics differed significantly among burn treatments. Sites burned the previous growing season had low vegetation density near the ground, vegetation taller than 1.0 m, and high seed abundance. These variables were all highly correlated with Henslows Sparrow relative abundance, but seed density best predicted Henslows Sparrow numbers. We recommend a biennial, rotational burn regime to maintain habitat characteristics correlated with Henslows Sparrow abundance.

SEX-BIASED WINTER DISTRIBUTION AND TIMING OF MIGRATION OF HERMIT THRUSHES (CATHARUS GUTTATUS) IN EASTERN NORTH AMERICA

Abstract We analyzed distribution of Hermit Thrushes (Catharus guttatus faxoni) wintering in the eastern United States and northeastern Mexico using data from 2,077 specimens collected in winter or during migration. Hermit Thrushes collected in winter showed a sex-biased latitudinal distribution, with the female mean 1.2° south of the male mean. Three general, nonmutually exclusive hypotheses have been proposed to account for that pattern in other species: (1) dominance of males over females, which forces females to lower latitudes; (2) larger body size of males, which permits males to overwinter in colder areas; and (3) earlier arrival by males on breeding grounds, which selects for males to winter closer to the breeding grounds. The dominance hypothesis requires that females be subordinate, an assumption that is not supported by previous research with wintering Hermit Thrushes. We also found no difference in sex ratio among habitats, despite strong differences in habitat quality. The body-size hypothesis requires that the larger sex be able to withstand colder temperatures. Male Hermit Thrushes are larger, but neither multiyear climate data nor weather in the specific month and year when birds were collected showed males to face significantly colder temperatures on the wintering grounds. Our data are most consistent with the arrival-time hypothesis. Males collected during spring migration migrated ∼20 days before females. When males began migrating in March, they experienced colder weather than sedentary females. By wintering farther north and migrating earlier, males expedite their return to their breeding grounds, although the small difference in winter distribution between the sexes is marginal compared to the effect of males’ much earlier departure. Presumably, any cost to males of wintering or migrating under more demanding conditions is balanced by the advantage of early arrival on the breeding grounds.