Earlier nesting by generalist predatory bird is associated with human responses to climate change

Abstract

Summary1. Warming temperatures cause temporal changes in growing seasons and prey abundance that drive earlier breeding by birds, especially dietary specialists within homogeneous habitat. Less is known about how generalists respond to climate-associated shifts in growing seasons or prey phenology, which may occur at different rates across land cover types. 2. We studied whether breeding phenology of a generalist predator, the American kestrel (Falco sparverius), was associated with shifts in growing seasons and, presumably, prey abundance, in a mosaic of non-irrigated shrub/grasslands and irrigated crops/pastures. We examined the relationship between remotely-sensed normalized difference vegetation index (NDVI) and abundance of small mammals that, with insects, constitute approximately 93% of kestrel diet biomass. We used NDVI to estimate the start of the growing season (SoGS) in irrigated and non-irrigated lands from 1992 to 2015 and tested whether either estimate of annual SoGS predicted the timing of kestrel nesting. Finally, we examined relationships among irrigated SoGS, weather and crop planting. 3. NDVI was a useful proxy for kestrel prey because it predicted small mammal abundance and past studies showed that NDVI predicts insect abundance. NDVI-estimated SoGS advanced significantly in irrigated lands (b = À1Á09 AE 0Á30 SE) but not in non-irrigated lands (b = À0Á57 AE 0Á53). Average date of kestrel nesting advanced 15 days in the past 24 years and was positively associated with the SoGS in irrigated lands, but not the SoGS in non-irrigated lands. Advanced SoGS in irrigated lands was related to earlier planting of crops after relatively warm winters, which were more common in recent years. 4. Despite different patterns of SoGS change between land cover types, kestrel nesting phenology shifted with earlier prey availability in irrigated lands. Kestrels may preferentially track prey in irrigated lands over non-irrigated lands because of higher quality prey on irrigated lands, or earlier prey abundance may release former constraints on other selective pressures to breed early, such as seasonal declines in fecundity or competition for high-quality mates. 5. This is one of the first examples of an association between human adaptation to climate change and shifts in breeding phenology of wildlife.

Warming springs and habitat alteration interact to impact timing of breeding and population dynamics in a migratory bird

“…Mowing alters reproductive outputs (Grüebler, Schuler, Horch, & Spaar, 2012;Kragten & De Snoo, 2007;Schekkerman, Teunissen, & Oosterveld, 2008) by placing nests at risk of physical destruction as well as reducing available cover of remaining nests (Kentie, Both, Hooijmeijer, & Piersma, 2015), and cover and food availability for the precocial chicks (Kentie, Hooijmeijer, Trimbos, Groen, & Piersma, 2013;Schekkerman & Beintema, 2007). These climatic and land use changes are associated with advanced arrival dates and timing of reproduction in species that reproduce on agricultural landscapes (Brandsma, Kentie, & Piersma, 2017;Gill et al, 2014;Smith, Steenhof, Mcclure, & Heath, 2017).…”

Weather and agricultural intensification determine the breeding performance of a small generalist predator

“…However, experimental studies suggest that warmer temperatures can affect directly the onset of laying in birds, probably linked to the activation of determined physiological processes 55 . In the northern hemisphere, American kestrels respond to primary production related to changes in food availability advancing their nesting phenology in areas of irrigated crops, where the growing season has advanced because farmers plant their crops earlier after warmer winters 57 . Mean clutch size, 4.48 eggs in our study area was similar to those registered in North America populations that are usually between 4-5 eggs, but more close to 4 in southern latitudes (e.g.…”

How Technology Can Transform Wildlife Conservation

“…For example, Connors et al [32] used track plates to measure abundance and local predation risk created by white-footed mouse (Peromyscus leucopus) foraging activity, and they conclude that such devices were a trustworthy means of quantifying local risk of attack by terrestrial mammals without significantly modifying the spatial distribution of risk. A more recent study by Smith et al [33] confirms that a well-designed trap to enclose the track plate can be fairly inexpensive, nonintrusive, and an easy monitoring tool. They specifically looked at whether breeding phenology of a generalist predator was associated with human responses to climate change.…”