Abstract
Invasive species have come to the forefront of conservation biology as a major threat to native biodiversity. Habitats dominated by shrub honeysuckles (Lonicera spp.) in the United States have been characterized as “ecological traps” by ecologists. Here we tested this hypothesis by investigating the effects of shrub honeysuckles on the nesting ecology of native birds in seven study sites in central Pennsylvania, USA. We examined how the abundance of shrub honeysuckles influenced the selection of nesting substrates and habitat for a community of common songbirds, and the parental-care behavior and nestling development of gray catbirds (Dumetella carolinensis). We found that birds had a strong bias towards nesting in honeysuckle shrubs, but not necessarily for nesting in honeysuckle-dominated habitats. Nest predation rates were affected by the density of nests in a habitat, but not by the overall abundance of honeysuckles in such habitats. Honeysuckle abundance in the habitat did show significant effects on some parental-care behavioral parameters: catbirds had higher nest visitation rates and shorter visit lengths in areas of high honeysuckle density. On average, Gray catbirds fed fruit 12%±0.31 s.e. of their nestling-feeding bouts, mostly fruits of shrub honeysuckles. Nestlings in sites with high honeysuckle density also showed higher mass:tarsus ratios, suggesting a good (possibly better) physiological condition of catbird nestlings at the time of fledging. Our study shows that honeysuckle-dominated habitats could have equivocal effects on nesting parameters of common species of native birds. We advise more caution in the widespread denomination of novel plant communities with high densities of honeysuckle as “ecological traps” as effects can be null or positive on native birds in certain localities.
Highlights
The ecological interaction between invasive plant species and bird communities has received a fair amount of attention over the past fifteen years [1]
The ecological trap hypothesis is supported in that a focal bird species – the gray catbird – modified its nest-tending behavior in unfavorable ways when breeding in habitats of high honeysuckle abundance (HSD) as compared to nesting in habitats dominated by native shrub species (NAT)
In agreement with previous studies, that shrub-nesting birds in central Pennsylvania have a positive bias for building nests in shrub honeysuckles, but this tendency is unrelated to the habitatlevel abundance of honeysuckle, or to predation rates
Summary
The ecological interaction between invasive plant species and bird communities has received a fair amount of attention over the past fifteen years [1]. It is increasingly recognized that the effects of these relationships are often species specific, context-dependent, and often involving mixes of positive and negative effects [1,2,3,4]. It is critical to better understand the outcomes and complexities of invasive plant-native bird interactions to create and implement effective conservation practices on landscapes with a long history of human disturbance and novel mixes of introduced and native species [1], [3]. The ecological effects of shrub honeysuckles are largely viewed as detrimental despite widespread use – and effective dispersal – by many native songbird species [8,9]
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