Bird Community Dynamics in a Temperate Deciduous Forest: Long‐Term Trends at Hubbard Brook

Abstract

Changes in species composition and abundance of birds breeding in an unfragmented temperate deciduous forest in New Hampshire, USA, were studied intensively during 16 consecutive breeding seasons, 1969-1984. The number of species breeding in the 10-ha study area in any one year varied from 17 to 28, and averaged 24. Total numbers of individuals breeding on the 1 0-ha plot ranged from 214 to 89, with many species (70%) declining during the 16-yr period. Overall, there was significant positive covariation among population trends of all species, suggesting a major, perhaps single, factor affecting population levels, such as weather or food supply. No two species, however, had identical patterns of change across all 16 yr. Thus, populations in this forest fluctuated largely independently of one another, suggesting a different combination of regulatory factors for each species. The major factors pulsing or stressing bird populations in this forest included: (1) changes in food abundance due largely to irruptions of defoliating Lepidoptera (most bird species, but especially vireos and warblers), (2) harsh late spring and summer weather (Scarlet Tanager, American Redstart), (3) changes in habitat structure related to forest succession (Least Flycatcher, Philadelphia Vireo), (4) interspecific interactions, particularly interference competition (Least Flycatcher-American Redstart, Red-eyed Vireo-Philadelphia Vireo), and (5) mortality during winter for both resident and migrant populations (Hermit Thrush, Dark-eyed Junco, permanent resident species such as woodpeckers and nuthatches.Some, but not all, irruptions of defoliating Lepidoptera significantly influenced many bird populations in this forest and contributed to the observed positive covariation in abundances. These irruptions produced pulses offood for breeding birds, but occurred at long and variable time intervals. Between outbreaks, food may regularly limit reproductive output of these forest birds, and low food abundance, along with the effects of predators, weather, and other mortality factors, contributes to high variability in bird reproductive success, which ultimately influences population size. Competition may also beome important during these periods of food scarcity. We therefore propose that birds in these temperate deciduous forests experience periods of prolonged food limitation, interrupted by relatively brief periods of superabundant food, a pattern contrasting with that described for other temperate systems (e.g., by Wiens 1977).From this examination of bird community dynamics on one site over many years, it is apparent that each species responds to its environment in a unique way, as determined by a variety of influences on its populations. Some of these operate on a local scale (e.g., vegetation structure, food abundance, interspecific competitors), while others function at regional (e.g., some weather effects) and global (e.g., winter events) geographic scales. These influences also differ as to their temporal persistence and predictability, and...

The influence of climate on the timing and rate of spring bird migration

“…Furthermore, tailwinds are thought to be more common in El Nino years, which also tend to be warmer years, and the opposite may also be true in La Nina years. Colder springs may also be the result of the occasional late winter storm and can also cause high levels of mortality (Holmes et al 1986) or possibly slow down migration by reducing foraging opportunities and the ability of migratory birds to rebuild fat stores critical for migration.…”

The Biogeochemistry of Carbon at Hubbard Brook

“…However, during periodic irruptions, defoliating caterpillars (e.g., Heterocampa guttivita Walker) consume a large proportion of foliage production (estimated at 44% in 1969-1971 at the HBEF; Gosz et al 1978). Continued observation of lepidopteran populations at the HBEF have not seen a repetition of the 1969-1971 outbreak, and the long-term average C flux through leaf-eating insects is relatively small (Holmes et al 1986; R.T. Holmes, unpublished data). The influence of insect-gleaning birds on this C flux has been demonstrated experimentally at the HBEF: birds can significantly reduce caterpillar abundance during midsummer when bird activity is greatest (Holmes et al 1979;Holmes 1990;Strong et al 2000).…”

Experimental food supplementation reveals habitat-dependent male reproductive investment in a migratory bird

“…Black-throated blue warblers are insectivorous during the breeding season, feeding extensively on adult and larval Lepidoptera taken mostly from the surfaces of leaves in the understory and sub-canopy [35,36], and deliver mostly Lepidoptera larvae to their nestlings [37]. The index of food availability was a function of caterpillar biomass per leaf and the estimated number of understory leaves per territory (see the electronic supplementary material for details).…”