Nocturnal nest predation: a potential obstacle to recovery of a Florida Scrub-Jay population

Abstract

Population declines among birds are often linked to habitat change and associated increases in nest predation rates. In species of conservation concern identifying nest predators is an important first step in developing management strategies to mitigate low nesting success caused by depredation. Because predator composition varies geographically and with landscape factors habitat restoration may need to be tailored to reduce locally important predators. We used miniature video cameras to identify nest predators in a population of Florida Scrub-Jays (Aphelocoma coerulescens) significant to conservation. At 22 nests we observed 25 predation events; 22 (88%) of these events were nocturnal. Yellow rat snakes (Elaphe obsoleta) had the highest daily predation rate and accounted for 76% of egg and nestling losses. Florida Scrub-Jays are vulnerable to nocturnal nest predation because their vigilance behavior is ineffective against nocturnal predators, breeders cannot defend against nocturnal predators, and brooding females are at risk of being killed by nocturnal predators. If current habitat restoration efforts do not reduce numbers of yellow rat snakes and improve scrub-jay nesting success, management actions to reduce populations of nocturnal snakes may need to be considered. SINOPSIS. Depredación nocturna de nidos: un obstáculo potencial para la recuperación de las poblaciones de Aphelocoma coerulescensLa reducción en números poblacionales de aves muchas veces ha sido ligada a cambios en el hábitat y aumentos en las tasas de depredación. En especies en donde hay preocupación por su conservación, el identificar los depredadores de nidos es un paso importante en el desarrollo de estrategias de manejo para mitigar el bajoéxito de anidamiento causado por los depredadores. Dado el caso de que la composición de depredadores varía geográficamente y con factores asociados al paisaje, la restauración del hábitat tiene que ser ajustada a modo de reducir depredadores locales que causen gran impacto negativo. Utilizamos cámaras de video en miniatura para identificar los depredadores de nidos en una poblacion de Aphelocoma coerulescens. Observamos 25 episodios de depredación (22 de ellos nocturnos) en 22 nidos estudiados. La culebra Elaphe obsoleta tuvo la tasa más alta de depredación y fue la responsable del 76% de la pérdida de huevos y pichones. Las aves estudiadas resultaron ser muy vulnerables a depredación nocturna, dado el caso de que su vigilancia es inefectiva contra los depredadores nocturnos. Inclusive las hembras que calientan los pichones entran en riesgo de ser depredadas. Si la restauración de hábitat no reduce el número de culebras y mejora eléxito de anidamiento del ave estudiada, se deben considerar acciones de manejo dirigidas a reducir la población de estas culebras.

The difference between night and day: antipredator behavior in birds

“…Despite the high risk of nocturnal predation (Isbell 1990;Stake and Cimprich 2003;Carter et al 2007;Reidy et al 2009), animals must find a balance between vigilance and sleep (Lima et al 2005) and this balance is likely to affect their antipredator behavior. During sleep, animals can still be responsive to potential dangers but this depends on their sleep state and the type of danger (Velluti 1997;Coenen and Drinkenburg 2002).…”

“…Anecdotal reports indicate that diurnal primates and birds sometimes emit vocalizations in response to nocturnal threats but do not seem to mob the predators (Vessey 1973;Busse 1980; reviewed by Southern et al 1982;Shealer and Kress 1991;Carter et al 2007). For example, ring-billed gulls emitted alarm calls when they were disturbed at night and fled from the area (Emlen et al 1966;Southern et al 1982).…”

Foraging behaviour of nest predators at open-cup nests of woodland passerines

“…The only comparable studies of European woodland songbirds reported either predominantly (Schaefer 2004) or exclusively (Stevens et al 2008) diurnal predation, as most nests in these studies were depredated by Jays. Distinctly different diel patterns were reported from other systems with different principal predators: mainly nocturnal predation by carnivores on wader nests in grasslands (MacDonald and Bolton 2008;Teunissen et al 2008) and Skylark Alauda arvensis nests in arable fields (Morris and Gilroy 2008), mainly nocturnal predation by snakes (Carter et al 2007) or mainly diurnal predation by sciurid rodents and raptors (Liebezeit and George 2002) on arboreal nests. The all-day predation by mammals was not only due to the occurrence of both nocturnal and diurnal species.…”

Nocturnal songs in a diurnal passerine: attracting mates or repelling intruders?

“…These rare vocalizations may be ineffective at repelling intruders or attracting mates. A more parsimonious explanation for these rare nocturnal vocalizations may be an individual's reaction to a disturbance event, such as nest predation (as seen in some species; jays, Aphelocoma coerulescens: Carter, Legare, Breininger, & Oddy, 2007;peahens, Pavo cristatus: Yorzinski & Platt, 2012) or environmental factors, such as moonlight (York, Young, & Radford, 2014). However, recent work has demonstrated seasonal variation in the occurrence of nocturnal songs in the field sparrow, Spizella pusilla, a species that rarely sings at night (Celis-Murillo, Stodola, Pappadopoli, Burton, & Ward, 2016), potentially indicating a role of nocturnal singing in reproductive activities.…”