Nest-site competition between invasive and native cavity nesting birds and its implication for conservation

Abstract

Nesting cavities are often a limited resource that multiple species use. There is an ongoing discussion on whether invasive cavity nesting birds restrict the availability of this key limited resource. While the answer to this question has important conservation implications, little experimental work has been done to examine it. Here, we aimed to experimentally test whether alien cavity nesting birds affect the occupancy of cavities and the resulting breeding success of native cavity breeders in a large urban park located in Tel Aviv, Israel. Over three breeding seasons, we manipulated the entry size of nest boxes and compared the occupancy and breeding success of birds in nest boxes of two treatments. These included nest boxes with large-entrance and small-entrance holes. The large-entrance holes allowed access for both the native and invasive birds (the two main aliens in the park are the common mynas and rose-ringed parakeets). The smaller-entrance boxes, on the other hand, allowed only the smaller sized native cavity breeders (great tits and house sparrows) to enter the boxes but prevented the alien species from entering. We found that the large-entrance nest boxes were occupied by five different bird species, comprising three natives (great tit, house sparrow, Scops owl) and two invasive species (common myna, rose-ringed parakeet) while the small-entrance boxes were only occupied by the two native species. The alien common mynas and rose-ringed parakeets occupied 77.5% of the large-entrance nest boxes whereas native species, mainly great tits, occupied less than 9% of the large-entrance boxes and 36.5% of the small-entrance boxes. When examining the occupancy of those cavities that were not occupied by the aliens, natives occupied both the small and large-entrance nest boxes equally. Three quarters (78%) of the great tits breeding in the large-entrance boxes were usurped by common mynas during the breeding season and as a result breeding success was significantly lower for great tits breeding in the large-entrance boxes compared with the small-entrance boxes. The results of this study suggests that the invasive alien species can reduce the breeding potential of native cavity breeders both by exploiting the limited breeding resource (nest cavities) and by directly usurping cavities already occupied by the native species. Since the majority of large-entrance nest boxes were occupied by the larger alien birds, less native species bred in the limited number of unoccupied large-entrance nest boxes because of exploitation competition. We propose that for management purposes, nest-box programs that alter the entrance size of available natural cavities may be a practical approach, reducing the competition between native cavity breeders and alien invasive birds, and especially benefiting the smaller native cavity breeders.

Chainsaw-Carved Cavities Better Mimic the Thermal Properties of Natural Tree Hollows than Nest Boxes and Log Hollows

“…For example, long-term monitoring of bat boxes in Melbourne, Australia has shown that, despite the provision of boxes constructed from materials with a range of insulative properties (ranging from 12 mm plywood to 90 mm pine), box use was dominated by one widespread, urban-adapted species, Gould's wattled bat Chalinolobus gouldii (Gray, 1841) [71]. Further research is required to investigate whether there is a link between the thermal profiles in nest boxes (compared to tree hollows) deployed in disturbed landscapes and their disproportionate level of use by widespread, highly adaptable species of birds [29,93,94] and mammals [21,71,95,96]. Field-based studies examining rates of occupation of chainsaw hollows and log hollows by target species versus undesirable exotic species would be of great interest, particularly in urban and peri-urban landscapes where nest box programs are often undertaken by land managers and conservation-focused community groups [4,97].…”

Nest usurpation by non‐native birds and the role of people in nest box management

“…These activities may include a variety of active and passive management actions targeting non‐native species, such as trapping and euthanasia, removing nests or eggs, shooting adults, or modifying the nest box (Larson et al, ). We define active management as lethal techniques such as euthanizing birds (Grarock, Tidemann, Wood, & Lindenmayer, ; Weitzel, ), removing nests or eggs, oiling or addling eggs (Fernandez‐Duque, Bailey, & Bonter, ; Hindman, Harvey, & Conley, ), and we define passive management as nonlethal techniques, such as reducing entrance hole sizes to exclude unwanted species based on body size (Charter, Izhaki, Ben Mocha, & Kark, ). Invasive bird management is legal (i.e., no permit necessary) under the Migratory Bird Treaty Act of 1918 in the United States and the Migratory Birds Convention Act of 1994 of Canada, both of which only protect species native to North America.…”

Nest site availability and niche differentiation between two cavity‐nesting birds in time and space

“…For passerine birds, especially those species that are secondary cavity nesting, nest sites are crucial aspects of their life histories; competition for nest sites must be severe, because (a) such species build nests in cavities as places for incubating their eggs and rearing their offspring, and (b) they cannot excavate cavities by themselves, but instead search for ready‐made holes that are generally limiting resources in nature. Although previous studies have demonstrated some nest site competition within or among birds, most of those studies focused on the conservation issue due to nest competition between introduced and native species (Charter, Izhaki, Ben Mocha, & Kark, ; Heinsohn, Murphy, & Legge, ; Hernandez‐Brito, Carrete, Ibanez, Juste, & Tella, ; Ingold, ; Kerpez & Smith, ).Very few studies have investigated the effect of nest‐site competition on habitat overlap (Minot & Perrins, ).…”