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How do post-industrial landscapes affect American Woodcock breeding success? Farley, Kathleen.. Rutgers University, 28 Nov 2016. Experiment. doi: 10.18258/8542
Aim 1: Determine whether courting males can distinguish differences in habitat quality between post-industrial and non-industrial early successional landscapes.
To determine how accurately American Woodcock perceive the quality of available habitat, I will calculate the proportion of dominant males within post-industrial landscapes and non-industrial sites. If more older males prefer post-industrial sites, then their perception is that post-industrial habitat is superior to non-industrial. If the males prefer post industrial sites, but suffer (higher mortality rates as adults or shorter display seasons), then it is a poor habitat.
In order to determine the relationship between habitat preference and quality, I will complete a mark-recapture study over two to three breeding seasons (March-April). Anticipated sample size is a minimum 20 individuals per age class and habitat (McAuley, Longcore, & Sepek, 1993).
Aim 2: Determine whether post-industrial landscapes are source, sink or ecological traps for offspring.
Unlike their parents, nestlings have no choice regarding the quality of the habitat where they hatch. Yet, fledgling success is dependent on actual habitat quality. Higher quality habitats will yield a higher chick to adult ratio (Johnson, 2007). Nestling health and survival rate until dispersal for migration will indicate whether post-industrial sites act as an ecological trap for offspring as woodcock need to achieve a minimum weight in order to migrate.
American Woodcock chicks are semi-precocial, leaving the nest within 4-5 hours of hatching, but remaining within 300m of the nest for the first two days (Ammann, 1963; Innes, 2010). Nestlings remain as a brood with the female for 1-2 weeks and are not capable of flight during this time (Ammann, 1963; Innes, 2010). Because American Woodcock are determinate egg layers, any clutch size less than four indicates a partial loss (Innes, 2010).
American Woodcock are cryptic species, meaning that they can be incredibly difficult to find. However, as they are also a game species, there has been considerable interest in their population status for decades. As such, much is known about locating these elusive birds. This knowledge will be used to improve the odds of locating them in two ways:
1. The males: To capture the males, there is about an hour window each evening throughout the spring where the males are too busy showing off to notice researchers lurking. This is when we hope to capture most of the males in order to conduct our study. However, if we do not get enough males, or they elude us, there's still hope.
We will have a second opportunity to capture males at the end of the breeding season. After breeding, migratory birds will typically molt before departing south. During the woodcock molt, flight requires too much energy and the adults will walk rather than fly. Thus, at night, we will be able to cartoon style sneak up on them with large nets. If we are unable to acquire sufficient numbers of woodcock in the early spring, we will have this second window later in the season.
2. The nestlings: In order to study the chicks, the most effective way is to work with a woodcock dog. These dogs, used for hunting, are trained to locate broods. Use of dogs in research is increasing for cryptic and rare species (Gorillas, Spotted Owls). Dogs will increase the number of nets found and decrease the number of days in the field.
To determine preference, we will work from the assumptions that (1) older birds are capable of acquiring and holding on to better territory and (2) birds will return to the same region each year because they have high site fidelity.
To determine how post-industrial sites contribute to population growth or decline, Program MARK, a mark-recapture program, will be used to calculate survival and fidelity estimates (Cooch & White, 2002). The fidelity and habitat types component is particularly relevant as when inputting the individual encounter histories, the encounters can be analyzed by habitat choice. The fidelity parameter can be used to determine how birds shift between post-industrial or early successional habitat to determine if there if flow is bidirectional regardless of age (equal-preference), if birds choose post-industrial sites as they age (severe trap) or if birds learn to avoid post-industrial sites (one-time trap). All together we will be able to get a sense of whether there is a net population growth or loss.
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