Fight or Flight: Parental Decisions about Predators at Nests of Northern Bobwhites (Colinus virginianus)

Patterns of nest defense against predators by ground-nesting bird species in the wild are poorly understood, largely because of a historical inability to directly monitor nests. Most nest-defense studies have observed responses elicited from artificial predators or human observers presented to nesting birds, and few have attempted to present these events in the context of predator—prey relationships found in the wild. We hypothesized that predator threat level (e.g., the threat posed to the clutch or to the clutch and the attending adult), parental characteristics, clutch investment, and future reproductive opportunities would influence avian nest-defense decisions. During 1999–2006, we examined predation events (n = 242) from 790 video-monitored Northern Bobwhite (Colinus virginianus) nests. We evaluated parental, predator, daily, and seasonal correlates that potentially contributed to patterns of nest defense by Northern Bobwhites using a model selection approach. The top model showed that nest defense was strongest at nests with larger predators that posed a threat to both adults and the clutch. This model also contained clutch size, but parameter estimates suggest that predator type was the only significant factor determining rates of nest defense. Our results suggest that Northern Bobwhites use the threat posed to the nest and the attending adult by the approaching predator as the primary cue in decisions to engage in nest defense

Patterns of Incubation Behavior in Northern Bobwhites (\u3ci\u3eColinus virginianus\u3c/i\u3e)

Patterns of incubation and nesting behavior for many species of birds, especially those with cryptic nests, have been difficult to obtain due to logistical and technological limitations. As a result, little is known about the daily attendance rhythms and behavioral patterns of many species, including the Northern Bobwhite (Colinus virginianus), despite this species being one of the most studied birds in the world. Incubation represents parental investment in offspring, and a multitude of factors may affect investment behaviors, including reproductive ecology, sex and age of parent, habitat quality, clutch age, and timing in the nesting season. Most Northern Bobwhite nests are incubated by a single adult, most often by females, but also by some males. We assessed the nest attendance patterns and parental investment in bob-white clutches (n 118) using continuous near-infrared video of nests being incubated by male or female bobwhites. We found that incubating parents took 0 –3 recesses per day. A single recess was most common for 87% of nest-days, and most of these were during mid-day to late afternoon (12:00 19:00). Mean total daily recess time was 182 min (95% CI: 98–264) for nests that hatched and 224 min (95% CI: 140–308) for nests that failed. We observed no difference between sexes in the number or length of recesses taken, but females initiated recess later in the day (median start time 15:00) than males (median start time 14:00). We found that nest recess length decreased as the clutch got older and increased as the nesting season progressed. Video surveillance systems proved to be a use-ful tool for observing and quantifying patterns of incubation behavior in a ground-nesting species with cryptic nests

Patterns of Incubation Behavior in Northern Bobwhites (\u3ci\u3eColinus virginianus\u3c/i\u3e)

Patterns of incubation and nesting behavior for many species of birds, especially those with cryptic nests, have been difficult to obtain due to logistical and technological limitations. As a result, little is known about the daily attendance rhythms and behavioral patterns of many species, including the Northern Bobwhite (Colinus virginianus), despite this species being one of the most studied birds in the world. Incubation represents parental investment in offspring, and a multitude of factors may affect investment behaviors, including reproductive ecology, sex and age of parent, habitat quality, clutch age, and timing in the nesting season. Most Northern Bobwhite nests are incubated by a single adult, most often by females, but also by some males. We assessed the nest attendance patterns and parental investment in bob-white clutches (n 118) using continuous near-infrared video of nests being incubated by male or female bobwhites. We found that incubating parents took 0 –3 recesses per day. A single recess was most common for 87% of nest-days, and most of these were during mid-day to late afternoon (12:00 19:00). Mean total daily recess time was 182 min (95% CI: 98–264) for nests that hatched and 224 min (95% CI: 140–308) for nests that failed. We observed no difference between sexes in the number or length of recesses taken, but females initiated recess later in the day (median start time 15:00) than males (median start time 14:00). We found that nest recess length decreased as the clutch got older and increased as the nesting season progressed. Video surveillance systems proved to be a use-ful tool for observing and quantifying patterns of incubation behavior in a ground-nesting species with cryptic nests

FIGHT OR FLIGHT: PARENTAL DECISIONS ABOUT PREDATORS AT NESTS OF NORTHERN BOBWHITES (COLINUS VIRGINIANUS)

Patterns of nest defense against predators by ground-nesting bird species in the wild are poorly understood, largely because of a historical inability to directly monitor nests. Most nest-defense studies have observed responses elicited from artificial predators or human observers presented to nesting birds, and few have attempted to present these events in the context of predator–prey relationships found in the wild. We hypothesized that predator threat level (e.g., the threat posed to the clutch or to the clutch and the attending adult), parental characteristics, clutch investment, and future reproductive opportunities would influence avian nest-defense decisions. During 1999–2006, we examined predation events (n = 242) from 790 video-monitored Northern Bobwhite (Colinus virginianus) nests. We evaluated parental, predator, daily, and seasonal correlates that potentially contributed to patterns of nest defense by Northern Bobwhites using a model selection approach. The top model showed that nest defense was strongest at nests with larger predators that posed a threat to both adults and the clutch. This model also contained clutch size, but parameter estimates suggest that predator type was the only significant factor determining rates of nest defense. Our results suggest that Northern Bobwhites use the threat posed to the nest and the attending adult by the approaching predator as the primary cue in decisions to engage in nest defense. Los patrones de defensa del nido contra depredadores por parte de especies de aves silvestres que anidan en el suelo son pobremente entendidos, en gran parte debido a una inhabilidad histórica para monitorear directamente los nidos. La mayoría de estudios de defensa del nido han observado respuestas desencadenadas por depredadores artificiales o por observadores humanos que se presentan a las aves anidantes, y pocos han intentado presentar dichos eventos en el contexto de las relaciones depredador-presa que se encuentran en condiciones silvestres. Planteamos la hipótesis de que el nivel de amenaza del depredador (e.g. la amenaza impuesta a la nidada o a la nidada y al adulto que cuida de ella), las características de los padres, la inversión en la nidada, y las oportunidades futuras de reproducirse podrían influenciar las decisiones de defensa del nido de las aves. Entre 1999 y 2006 examinamos los eventos de depredación (n = 242) de 790 nidos de Colinus virginianus monitoreados en vídeo. Evaluamos las variables parentales, del depredador, diarias y estacionales que potencialmente contribuyen a los patrones de defensa del nido por C. virginianus usando una aproximación de selección de modelos. El mejor modelo mostró que la defensa del nido fue más fuerte en nidos con depredadores más grandes que amenazaban a la nidada y al adulto que cuidaba de ella. Este modelo también incluyó el tamaño de la nidada, pero los parámetros estimados sugieren que el tipo de depredador fue el único factor que afecta significativamente las tasas de defensa del nido. Nuestros resultados sugieren que C. virginianus usa la amenaza impuesta por el depredador que se acerca al nido y al adulto que lo cuida como la pista primaria para la toma de decisiones sobre la defensa del nido

Partial Depredations on Northern Bobwhite Nests

Partial clutch loss following a predation event is rarely studied in ground-nesting birds despite predation often being the leading cause of nest failure. Partial nest depredation occurs when predators attack but leave some eggs intact. Using continuous video monitoring, we documented a total of 372 initial predation events at nests of Northern Bobwhites (Colinus virginianus). From these, we observed a sample of partial nest pre-dation events (n=47). Partial predation events resulted in three outcomes: (1) The nest failed due to parental abandonment; (2) adult stayed with the nest, but clutch failed to hatch, usually due to further predation events; or (3) adult stayed with nest and the remaining eggs hatched, add-ing to the reproductive fitness of the adult. Most common predators causing partial depredations were ratsnakes (Pantherophis alleghaniensis and P. guttatus), kingsnakes (Lampropeltis getula), and fire ants (Solenopsis spp.). We used logistic regres-sion and model selection methods to assess six cues that parents may use to determine the value of remaining offspring and resulting abandon-ment decision. Overall, nests with fewer eggs remaining after the predation event or those pre-dated early in the incubation period were more likely to be abandoned; juveniles appeared more likely to abandon than adults. Future studies will be needed to confirm our findings of the relation-ships between cues and abandonment decisions, and video surveillance systems will be a necessary component of these studies