Temperature and Nestling Development: Temporal Variations in <i>Zonotrichia leucophrys oriantha</i> Feeding Frequency

Abstract

Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) are unique in that their nestlings, which require parental care for 9 days before fledging, have a 25% higher metabolic rate than other open-nesting passerines. This unusually high energetic demand requires that parents frequently feed their young; however, female sparrows must balance their time between bouts of foraging and incubating to protect vulnerable nestlings from extreme temperatures. I hypothesized that this tradeoff in parental nest attendance behavior varies on colder versus warmer days. In particular, feeding rates are reduced and/or delayed on cold mornings and on hot afternoons. These patterns would accommodate for incubation during early hours and shading from intense sun during afternoon hours. This was tested by monitoring Mountain White-crowned Sparrow nests with data loggers that recorded temperature every two minutes and a nest camera that revealed the frequency of different behaviors. Analysis showed a significant but extremely weak negative correlation between the frequency of feeding and temperature (R2 = 0.063831, p = 0.0042) and between the proportion of time parents were absent from the nest and temperature (R2 = 0.047224, p = 0.0141). ANOVAs of both temperature with feeding frequency and temperature with parental absence over 3.5 hour intervals revealed that cold mornings have higher feeding frequency but a lower proportion of parental absence than warm mornings. In cold afternoons, there is a higher feeding frequency but an equivalent proportion of parental absence as warm afternoons. However, only the difference in morning feeding frequency is significant (p = 0.03).

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